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Publisher: Elsevier   (Total: 3181 journals)

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Showing 1 - 200 of 3181 Journals sorted alphabetically
Academic Pediatrics     Hybrid Journal   (Followers: 39, SJR: 1.655, CiteScore: 2)
Academic Radiology     Hybrid Journal   (Followers: 26, SJR: 1.015, CiteScore: 2)
Accident Analysis & Prevention     Partially Free   (Followers: 105, SJR: 1.462, CiteScore: 3)
Accounting Forum     Hybrid Journal   (Followers: 28, SJR: 0.932, CiteScore: 2)
Accounting, Organizations and Society     Hybrid Journal   (Followers: 42, SJR: 1.771, CiteScore: 3)
Achievements in the Life Sciences     Open Access   (Followers: 7)
Acta Anaesthesiologica Taiwanica     Open Access   (Followers: 6)
Acta Astronautica     Hybrid Journal   (Followers: 443, SJR: 0.758, CiteScore: 2)
Acta Automatica Sinica     Full-text available via subscription   (Followers: 2)
Acta Biomaterialia     Hybrid Journal   (Followers: 29, SJR: 1.967, CiteScore: 7)
Acta Colombiana de Cuidado Intensivo     Full-text available via subscription   (Followers: 3)
Acta de Investigación Psicológica     Open Access   (Followers: 3)
Acta Ecologica Sinica     Open Access   (Followers: 11, SJR: 0.18, CiteScore: 1)
Acta Histochemica     Hybrid Journal   (Followers: 5, SJR: 0.661, CiteScore: 2)
Acta Materialia     Hybrid Journal   (Followers: 319, SJR: 3.263, CiteScore: 6)
Acta Mathematica Scientia     Full-text available via subscription   (Followers: 5, SJR: 0.504, CiteScore: 1)
Acta Mechanica Solida Sinica     Full-text available via subscription   (Followers: 9, SJR: 0.542, CiteScore: 1)
Acta Oecologica     Hybrid Journal   (Followers: 12, SJR: 0.834, CiteScore: 2)
Acta Otorrinolaringologica (English Edition)     Full-text available via subscription  
Acta Otorrinolaringológica Española     Full-text available via subscription   (Followers: 2, SJR: 0.307, CiteScore: 0)
Acta Pharmaceutica Sinica B     Open Access   (Followers: 2, SJR: 1.793, CiteScore: 6)
Acta Poética     Open Access   (Followers: 4, SJR: 0.101, CiteScore: 0)
Acta Psychologica     Hybrid Journal   (Followers: 26, SJR: 1.331, CiteScore: 2)
Acta Sociológica     Open Access   (Followers: 1)
Acta Tropica     Hybrid Journal   (Followers: 6, SJR: 1.052, CiteScore: 2)
Acta Urológica Portuguesa     Open Access  
Actas Dermo-Sifiliograficas     Full-text available via subscription   (Followers: 3, SJR: 0.374, CiteScore: 1)
Actas Dermo-Sifiliográficas (English Edition)     Full-text available via subscription   (Followers: 2)
Actas Urológicas Españolas     Full-text available via subscription   (Followers: 3, SJR: 0.344, CiteScore: 1)
Actas Urológicas Españolas (English Edition)     Full-text available via subscription   (Followers: 1)
Actualites Pharmaceutiques     Full-text available via subscription   (Followers: 7, SJR: 0.19, CiteScore: 0)
Actualites Pharmaceutiques Hospitalieres     Full-text available via subscription   (Followers: 3)
Acupuncture and Related Therapies     Hybrid Journal   (Followers: 8)
Acute Pain     Full-text available via subscription   (Followers: 15, SJR: 2.671, CiteScore: 5)
Ad Hoc Networks     Hybrid Journal   (Followers: 11, SJR: 0.53, CiteScore: 4)
Addictive Behaviors     Hybrid Journal   (Followers: 18, SJR: 1.29, CiteScore: 3)
Addictive Behaviors Reports     Open Access   (Followers: 9, SJR: 0.755, CiteScore: 2)
Additive Manufacturing     Hybrid Journal   (Followers: 11, SJR: 2.611, CiteScore: 8)
Additives for Polymers     Full-text available via subscription   (Followers: 23)
Advanced Drug Delivery Reviews     Hybrid Journal   (Followers: 187, SJR: 4.09, CiteScore: 13)
Advanced Engineering Informatics     Hybrid Journal   (Followers: 12, SJR: 1.167, CiteScore: 4)
Advanced Powder Technology     Hybrid Journal   (Followers: 17, SJR: 0.694, CiteScore: 3)
Advances in Accounting     Hybrid Journal   (Followers: 9, SJR: 0.277, CiteScore: 1)
Advances in Agronomy     Full-text available via subscription   (Followers: 17, SJR: 2.384, CiteScore: 5)
Advances in Anesthesia     Full-text available via subscription   (Followers: 30, SJR: 0.126, CiteScore: 0)
Advances in Antiviral Drug Design     Full-text available via subscription   (Followers: 2)
Advances in Applied Mathematics     Full-text available via subscription   (Followers: 12, SJR: 0.992, CiteScore: 1)
Advances in Applied Mechanics     Full-text available via subscription   (Followers: 12, SJR: 1.551, CiteScore: 4)
Advances in Applied Microbiology     Full-text available via subscription   (Followers: 24, SJR: 2.089, CiteScore: 5)
Advances In Atomic, Molecular, and Optical Physics     Full-text available via subscription   (Followers: 15, SJR: 0.572, CiteScore: 2)
Advances in Biological Regulation     Hybrid Journal   (Followers: 4, SJR: 2.61, CiteScore: 7)
Advances in Botanical Research     Full-text available via subscription   (Followers: 2, SJR: 0.686, CiteScore: 2)
Advances in Cancer Research     Full-text available via subscription   (Followers: 34, SJR: 3.043, CiteScore: 6)
Advances in Carbohydrate Chemistry and Biochemistry     Full-text available via subscription   (Followers: 9, SJR: 1.453, CiteScore: 2)
Advances in Catalysis     Full-text available via subscription   (Followers: 5, SJR: 1.992, CiteScore: 5)
Advances in Cell Aging and Gerontology     Full-text available via subscription   (Followers: 5)
Advances in Cellular and Molecular Biology of Membranes and Organelles     Full-text available via subscription   (Followers: 14)
Advances in Chemical Engineering     Full-text available via subscription   (Followers: 29, SJR: 0.156, CiteScore: 1)
Advances in Child Development and Behavior     Full-text available via subscription   (Followers: 11, SJR: 0.713, CiteScore: 1)
Advances in Chronic Kidney Disease     Full-text available via subscription   (Followers: 10, SJR: 1.316, CiteScore: 2)
Advances in Clinical Chemistry     Full-text available via subscription   (Followers: 26, SJR: 1.562, CiteScore: 3)
Advances in Colloid and Interface Science     Full-text available via subscription   (Followers: 20, SJR: 1.977, CiteScore: 8)
Advances in Computers     Full-text available via subscription   (Followers: 14, SJR: 0.205, CiteScore: 1)
Advances in Dermatology     Full-text available via subscription   (Followers: 15)
Advances in Developmental Biology     Full-text available via subscription   (Followers: 13)
Advances in Digestive Medicine     Open Access   (Followers: 12)
Advances in DNA Sequence-Specific Agents     Full-text available via subscription   (Followers: 7)
Advances in Drug Research     Full-text available via subscription   (Followers: 26)
Advances in Ecological Research     Full-text available via subscription   (Followers: 44, SJR: 2.524, CiteScore: 4)
Advances in Engineering Software     Hybrid Journal   (Followers: 29, SJR: 1.159, CiteScore: 4)
Advances in Experimental Biology     Full-text available via subscription   (Followers: 8)
Advances in Experimental Social Psychology     Full-text available via subscription   (Followers: 52, SJR: 5.39, CiteScore: 8)
Advances in Exploration Geophysics     Full-text available via subscription   (Followers: 1)
Advances in Fluorine Science     Full-text available via subscription   (Followers: 9)
Advances in Food and Nutrition Research     Full-text available via subscription   (Followers: 67, SJR: 0.591, CiteScore: 2)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 17)
Advances in Genetics     Full-text available via subscription   (Followers: 21, SJR: 1.354, CiteScore: 4)
Advances in Genome Biology     Full-text available via subscription   (Followers: 11, SJR: 12.74, CiteScore: 13)
Advances in Geophysics     Full-text available via subscription   (Followers: 7, SJR: 1.193, CiteScore: 3)
Advances in Heat Transfer     Full-text available via subscription   (Followers: 26, SJR: 0.368, CiteScore: 1)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 11, SJR: 0.749, CiteScore: 3)
Advances in Human Factors/Ergonomics     Full-text available via subscription   (Followers: 26)
Advances in Imaging and Electron Physics     Full-text available via subscription   (Followers: 3, SJR: 0.193, CiteScore: 0)
Advances in Immunology     Full-text available via subscription   (Followers: 37, SJR: 4.433, CiteScore: 6)
Advances in Inorganic Chemistry     Full-text available via subscription   (Followers: 10, SJR: 1.163, CiteScore: 2)
Advances in Insect Physiology     Full-text available via subscription   (Followers: 2, SJR: 1.938, CiteScore: 3)
Advances in Integrative Medicine     Hybrid Journal   (Followers: 6, SJR: 0.176, CiteScore: 0)
Advances in Intl. Accounting     Full-text available via subscription   (Followers: 3)
Advances in Life Course Research     Hybrid Journal   (Followers: 9, SJR: 0.682, CiteScore: 2)
Advances in Lipobiology     Full-text available via subscription   (Followers: 1)
Advances in Magnetic and Optical Resonance     Full-text available via subscription   (Followers: 8)
Advances in Marine Biology     Full-text available via subscription   (Followers: 21, SJR: 0.88, CiteScore: 2)
Advances in Mathematics     Full-text available via subscription   (Followers: 15, SJR: 3.027, CiteScore: 2)
Advances in Medical Sciences     Hybrid Journal   (Followers: 8, SJR: 0.694, CiteScore: 2)
Advances in Medicinal Chemistry     Full-text available via subscription   (Followers: 6)
Advances in Microbial Physiology     Full-text available via subscription   (Followers: 5, SJR: 1.158, CiteScore: 3)
Advances in Molecular and Cell Biology     Full-text available via subscription   (Followers: 25)
Advances in Molecular and Cellular Endocrinology     Full-text available via subscription   (Followers: 8)
Advances in Molecular Toxicology     Full-text available via subscription   (Followers: 7, SJR: 0.182, CiteScore: 0)
Advances in Nanoporous Materials     Full-text available via subscription   (Followers: 5)
Advances in Oncobiology     Full-text available via subscription   (Followers: 2)
Advances in Organ Biology     Full-text available via subscription   (Followers: 2)
Advances in Organometallic Chemistry     Full-text available via subscription   (Followers: 18, SJR: 1.875, CiteScore: 4)
Advances in Parallel Computing     Full-text available via subscription   (Followers: 7, SJR: 0.174, CiteScore: 0)
Advances in Parasitology     Full-text available via subscription   (Followers: 5, SJR: 1.579, CiteScore: 4)
Advances in Pediatrics     Full-text available via subscription   (Followers: 27, SJR: 0.461, CiteScore: 1)
Advances in Pharmaceutical Sciences     Full-text available via subscription   (Followers: 19)
Advances in Pharmacology     Full-text available via subscription   (Followers: 17, SJR: 1.536, CiteScore: 3)
Advances in Physical Organic Chemistry     Full-text available via subscription   (Followers: 9, SJR: 0.574, CiteScore: 1)
Advances in Phytomedicine     Full-text available via subscription  
Advances in Planar Lipid Bilayers and Liposomes     Full-text available via subscription   (Followers: 3, SJR: 0.109, CiteScore: 1)
Advances in Plant Biochemistry and Molecular Biology     Full-text available via subscription   (Followers: 10)
Advances in Plant Pathology     Full-text available via subscription   (Followers: 6)
Advances in Porous Media     Full-text available via subscription   (Followers: 5)
Advances in Protein Chemistry     Full-text available via subscription   (Followers: 19)
Advances in Protein Chemistry and Structural Biology     Full-text available via subscription   (Followers: 20, SJR: 0.791, CiteScore: 2)
Advances in Psychology     Full-text available via subscription   (Followers: 68)
Advances in Quantum Chemistry     Full-text available via subscription   (Followers: 6, SJR: 0.371, CiteScore: 1)
Advances in Radiation Oncology     Open Access   (Followers: 2, SJR: 0.263, CiteScore: 1)
Advances in Small Animal Medicine and Surgery     Hybrid Journal   (Followers: 3, SJR: 0.101, CiteScore: 0)
Advances in Space Biology and Medicine     Full-text available via subscription   (Followers: 6)
Advances in Space Research     Full-text available via subscription   (Followers: 423, SJR: 0.569, CiteScore: 2)
Advances in Structural Biology     Full-text available via subscription   (Followers: 5)
Advances in Surgery     Full-text available via subscription   (Followers: 13, SJR: 0.555, CiteScore: 2)
Advances in the Study of Behavior     Full-text available via subscription   (Followers: 38, SJR: 2.208, CiteScore: 4)
Advances in Veterinary Medicine     Full-text available via subscription   (Followers: 20)
Advances in Veterinary Science and Comparative Medicine     Full-text available via subscription   (Followers: 15)
Advances in Virus Research     Full-text available via subscription   (Followers: 6, SJR: 2.262, CiteScore: 5)
Advances in Water Resources     Hybrid Journal   (Followers: 54, SJR: 1.551, CiteScore: 3)
Aeolian Research     Hybrid Journal   (Followers: 6, SJR: 1.117, CiteScore: 3)
Aerospace Science and Technology     Hybrid Journal   (Followers: 383, SJR: 0.796, CiteScore: 3)
AEU - Intl. J. of Electronics and Communications     Hybrid Journal   (Followers: 8, SJR: 0.42, CiteScore: 2)
African J. of Emergency Medicine     Open Access   (Followers: 6, SJR: 0.296, CiteScore: 0)
Ageing Research Reviews     Hybrid Journal   (Followers: 12, SJR: 3.671, CiteScore: 9)
Aggression and Violent Behavior     Hybrid Journal   (Followers: 482, SJR: 1.238, CiteScore: 3)
Agri Gene     Hybrid Journal   (Followers: 1, SJR: 0.13, CiteScore: 0)
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 18, SJR: 1.818, CiteScore: 5)
Agricultural Systems     Hybrid Journal   (Followers: 31, SJR: 1.156, CiteScore: 4)
Agricultural Water Management     Hybrid Journal   (Followers: 44, SJR: 1.272, CiteScore: 3)
Agriculture and Agricultural Science Procedia     Open Access   (Followers: 4)
Agriculture and Natural Resources     Open Access   (Followers: 3)
Agriculture, Ecosystems & Environment     Hybrid Journal   (Followers: 58, SJR: 1.747, CiteScore: 4)
Ain Shams Engineering J.     Open Access   (Followers: 5, SJR: 0.589, CiteScore: 3)
Air Medical J.     Hybrid Journal   (Followers: 8, SJR: 0.26, CiteScore: 0)
AKCE Intl. J. of Graphs and Combinatorics     Open Access   (SJR: 0.19, CiteScore: 0)
Alcohol     Hybrid Journal   (Followers: 12, SJR: 1.153, CiteScore: 3)
Alcoholism and Drug Addiction     Open Access   (Followers: 12)
Alergologia Polska : Polish J. of Allergology     Full-text available via subscription   (Followers: 1)
Alexandria Engineering J.     Open Access   (Followers: 2, SJR: 0.604, CiteScore: 3)
Alexandria J. of Medicine     Open Access   (Followers: 1, SJR: 0.191, CiteScore: 1)
Algal Research     Partially Free   (Followers: 11, SJR: 1.142, CiteScore: 4)
Alkaloids: Chemical and Biological Perspectives     Full-text available via subscription   (Followers: 2)
Allergologia et Immunopathologia     Full-text available via subscription   (Followers: 1, SJR: 0.504, CiteScore: 1)
Allergology Intl.     Open Access   (Followers: 5, SJR: 1.148, CiteScore: 2)
Alpha Omegan     Full-text available via subscription   (SJR: 3.521, CiteScore: 6)
ALTER - European J. of Disability Research / Revue Européenne de Recherche sur le Handicap     Full-text available via subscription   (Followers: 11, SJR: 0.201, CiteScore: 1)
Alzheimer's & Dementia     Hybrid Journal   (Followers: 54, SJR: 4.66, CiteScore: 10)
Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring     Open Access   (Followers: 6, SJR: 1.796, CiteScore: 4)
Alzheimer's & Dementia: Translational Research & Clinical Interventions     Open Access   (Followers: 6, SJR: 1.108, CiteScore: 3)
Ambulatory Pediatrics     Hybrid Journal   (Followers: 5)
American Heart J.     Hybrid Journal   (Followers: 58, SJR: 3.267, CiteScore: 4)
American J. of Cardiology     Hybrid Journal   (Followers: 66, SJR: 1.93, CiteScore: 3)
American J. of Emergency Medicine     Hybrid Journal   (Followers: 47, SJR: 0.604, CiteScore: 1)
American J. of Geriatric Pharmacotherapy     Full-text available via subscription   (Followers: 13)
American J. of Geriatric Psychiatry     Hybrid Journal   (Followers: 14, SJR: 1.524, CiteScore: 3)
American J. of Human Genetics     Hybrid Journal   (Followers: 37, SJR: 7.45, CiteScore: 8)
American J. of Infection Control     Hybrid Journal   (Followers: 29, SJR: 1.062, CiteScore: 2)
American J. of Kidney Diseases     Hybrid Journal   (Followers: 36, SJR: 2.973, CiteScore: 4)
American J. of Medicine     Hybrid Journal   (Followers: 50)
American J. of Medicine Supplements     Full-text available via subscription   (Followers: 3, SJR: 1.967, CiteScore: 2)
American J. of Obstetrics and Gynecology     Hybrid Journal   (Followers: 266, SJR: 2.7, CiteScore: 4)
American J. of Ophthalmology     Hybrid Journal   (Followers: 66, SJR: 3.184, CiteScore: 4)
American J. of Ophthalmology Case Reports     Open Access   (Followers: 5, SJR: 0.265, CiteScore: 0)
American J. of Orthodontics and Dentofacial Orthopedics     Full-text available via subscription   (Followers: 6, SJR: 1.289, CiteScore: 1)
American J. of Otolaryngology     Hybrid Journal   (Followers: 25, SJR: 0.59, CiteScore: 1)
American J. of Pathology     Hybrid Journal   (Followers: 32, SJR: 2.139, CiteScore: 4)
American J. of Preventive Medicine     Hybrid Journal   (Followers: 28, SJR: 2.164, CiteScore: 4)
American J. of Surgery     Hybrid Journal   (Followers: 39, SJR: 1.141, CiteScore: 2)
American J. of the Medical Sciences     Hybrid Journal   (Followers: 12, SJR: 0.767, CiteScore: 1)
Ampersand : An Intl. J. of General and Applied Linguistics     Open Access   (Followers: 7)
Anaerobe     Hybrid Journal   (Followers: 4, SJR: 1.144, CiteScore: 3)
Anaesthesia & Intensive Care Medicine     Full-text available via subscription   (Followers: 67, SJR: 0.138, CiteScore: 0)
Anaesthesia Critical Care & Pain Medicine     Full-text available via subscription   (Followers: 25, SJR: 0.411, CiteScore: 1)
Anales de Cirugia Vascular     Full-text available via subscription   (Followers: 1)
Anales de Pediatría     Full-text available via subscription   (Followers: 3, SJR: 0.277, CiteScore: 0)
Anales de Pediatría (English Edition)     Full-text available via subscription  
Anales de Pediatría Continuada     Full-text available via subscription  
Analytic Methods in Accident Research     Hybrid Journal   (Followers: 5, SJR: 4.849, CiteScore: 10)
Analytica Chimica Acta     Hybrid Journal   (Followers: 44, SJR: 1.512, CiteScore: 5)
Analytica Chimica Acta : X     Open Access  
Analytical Biochemistry     Hybrid Journal   (Followers: 210, SJR: 0.633, CiteScore: 2)
Analytical Chemistry Research     Open Access   (Followers: 13, SJR: 0.411, CiteScore: 2)
Analytical Spectroscopy Library     Full-text available via subscription   (Followers: 14)
Anesthésie & Réanimation     Full-text available via subscription   (Followers: 2)
Anesthesiology Clinics     Full-text available via subscription   (Followers: 25, SJR: 0.683, CiteScore: 2)
Angiología     Full-text available via subscription   (SJR: 0.121, CiteScore: 0)
Angiologia e Cirurgia Vascular     Open Access   (Followers: 1, SJR: 0.111, CiteScore: 0)
Animal Behaviour     Hybrid Journal   (Followers: 226, SJR: 1.58, CiteScore: 3)
Animal Feed Science and Technology     Hybrid Journal   (Followers: 7, SJR: 0.937, CiteScore: 2)
Animal Reproduction Science     Hybrid Journal   (Followers: 7, SJR: 0.704, CiteScore: 2)

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Similar Journals
Journal Cover
Aerospace Science and Technology
Journal Prestige (SJR): 0.796
Citation Impact (citeScore): 3
Number of Followers: 383  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1270-9638
Published by Elsevier Homepage  [3181 journals]
  • A two-step method for system identification of low-cost quadrotor
    • Abstract: Publication date: Available online 15 November 2019Source: Aerospace Science and TechnologyAuthor(s): Yinan Yu, Pan Tang, Tao Song, Defu Lin
       
  • A semi-analytical approach on the effect of external lateral pressure on
           free vibration of joined sandwich aerospace composite conical-conical
           shells
    • Abstract: Publication date: Available online 15 November 2019Source: Aerospace Science and TechnologyAuthor(s): Ali Heidari Soureshjani, Roohollah Talebitooti, Mostafa Talebitooti This paper investigates the free vibrational behaviors of joined composite sandwich conical-conical shells under external lateral pressure. The corresponding equations are derived based on the first order shear deformation theory (FSDT). Herewith, free vibration equations are extracted via applying Hamilton's principle and considering initial mechanical stresses solved by static equilibrium equations. To establish the continuity of two conical shells, compatibility of displacements and stress resultants are satisfied at the junctions. The generalized differential quadrature (GDQ) method is adopted to discretize the governing equations for each conical segment, together with related boundary and continuity conditions in a meridian direction. In order to verify the results as well as representing the convergence of the presented approach, some pieces of case studies are accomplished. These studies provide a better exhibition of lateral pressure, cone angles and shell thickness influences on the free vibration of joined composite sandwich conical shells with various boundary conditions. Then, the effect of four different types of materials which are more applicable in pressurized environments such as underwater and submarine structures, i.e. polyetheretherketon (PEEK), polycarbonate (PC), solid propylene (SPP), and high density polyimide foam (HDPF) are investigated for the core layer. Critical buckling pressure in the present approach is obtained when the natural frequency takes the value of zero for the lowest pressure. Finally, the values of lateral pressure are selected considering the critical buckling pressure to avoid buckling occurrence.
       
  • Preference-driven Kriging-based multiobjective optimization method with a
           
    • Abstract: Publication date: Available online 14 November 2019Source: Aerospace Science and TechnologyAuthor(s): Youwei He, Jinju Sun, Peng Song, Xuesong Wang, Asif S. Usmani Multipoint infill sampling has emerged recently as a promising tool to enhance the efficiency of the adaptive Kriging-based optimization method for computational expensive multiobjective problems. However, the number of infill samples in each iteration in the open literature is up to 10. A novel multipoint infill criterion is proposed on the basis of Expected Angle-Penalized Length Improvement (EAPLI). One of its distinct features is that it makes the number of infill samples in each iteration increase tenfold along with a fair convergence speed by using multiple reference vectors to search for multiple infill points. Its implementation involves several major elements: firstly, angle-penalized length based improvement is established for each reference vector; then maximizing EAPLI is conducted for all vectors to obtain sufficient candidate infill points; finally, multiple infill points are selected from the candidate pool according to the candidate niche counts. Experimental results on benchmark test problems show that the proposed EAPLI criterion is highly competitive in comparison with other criteria. Then the performance of EAPLI using different numbers of multiple infill points, from several to tens and even a hundred, is studied. The other distinct feature of EAPLI is, the distribution of reference vectors can be manipulated to include the designer's preferences to perform preference-driven optimization, which can reduce searches towards solutions violating the preferences and thus further enhance the optimization efficiency. A preference-driven airfoil shape optimization method is established by integrating the EAPLI, free-form deformation method, and a flow solver. It is used to optimize the NACA0012 airfoil, by which the non-dominated solutions are fairly driven into the preferred subspaces with significant gains in both objectives of lift/drag coefficient ratio and drag coefficient simultaneously.
       
  • Propeller-wing coupled aerodynamic design based on desired propeller
           slipstream
    • Abstract: Publication date: Available online 14 November 2019Source: Aerospace Science and TechnologyAuthor(s): Xue Chen, Zhou Zhou Considering the multi-propeller characteristics of DEP configuration, the lift-to-drag ratio of the wing is improved by optimizing the slipstream of the propeller, rather than changing the chord length and twist distribution along the span of the wing. First, a propeller design method is proposed to obtain the target induced velocity distribution, and then, a calculation model Prop−wing of propeller-wing integration is established based on the designed induced velocity distribution and panel method. Finally, an efficient optimization algorithm based on genetic algorithm (GA) and Kriging surrogate modeling is used to optimize the induced velocity distribution of the slipstream for higher lift-to-drag ratios. The optimization results show that when the thrust is constant, the larger the axial induced velocity close to the hub, the better the drag characteristics of the wing. When the chord length of propeller is not limited, the drag decreases by 30.48% and the lift-to-drag ratio increases by 51.93%. A 13.68% drag reduction and 18.80% lift-to-drag ratio improvement can be obtained.
       
  • Unsteady influences of blade loading distribution on secondary flow of
           ultra-high-lift LPT
    • Abstract: Publication date: Available online 14 November 2019Source: Aerospace Science and TechnologyAuthor(s): Xiao Qu, Yanfeng Zhang, Xingen Lu, Junqiang Zhu Experimental measurements were performed to study the influence of blade loading distribution on the aerodynamic performance of an ultra-high-lift low-pressure turbine cascade (Zw = 1.58) in the presence and absence of incoming wakes. The flow structures in front-loaded and aft-loaded blade passages were comprehensively compared at various Reynolds numbers. Furthermore, the flow mechanisms responsible for the effect of the blade loading distribution on the secondary flow were discussed in detail through numerical calculations. At the low Reynolds number of 25,000, weaker secondary flow was observed for the aft-loaded blade under steady conditions owing to the lower cross-passage pressure gradient compared to the front-loaded blade. Unsteady wakes clearly improved the throughflow characteristics of the cascade passage, increased the blade loading, and strengthened the secondary flow in the aft-loaded blade passage. At the high Reynolds number of 100,000, unsteady wakes delayed generation of the passage vortex in both the front-loaded and aft-loaded blade passages and clearly weakened the secondary flow. The experimental results revealed that the upstream wakes reduced the strength of the passage vortex core in the aft-loaded and front-loaded blade profiles by 21.6% and 17.5%, respectively.
       
  • Investigation on two-stage vibration suppression and precision pointing
           for space optical payloads
    • Abstract: Publication date: Available online 13 November 2019Source: Aerospace Science and TechnologyAuthor(s): Hai Yun, Lei Liu, Qing Li, Hongjie Yang For space optical payloads, it is difficult to achieve vibration suppression and high precision pointing due to broadband range of micro-vibration. This paper thus presents one two-stage vibration suppression and precision pointing platform, which synthesizes the integrated vibration isolation of the transmission path and the payload end. The proposed two-stage platform consists of one piezoelectric-based Stewart platform and a fast steering mirror (FSM) subsystem. Based on the two-stage platform, the collaborative control strategy is presented. The Stewart platform is used to suppress the high-frequency structural vibrations by employing the least mean square (LMS) acceleration feedback algorithm. The FSM is applied to compensate the low-frequency jitters of optical axis and achieve high precision pointing control according to CCD measure information. In addition, the Stewart platform can offload the FSM and increase the pointing range of the system. Finally, the experimental prototype is developed and the experiments are implemented. The experimental results demonstrate the feasibility of the collaborative control scheme and further validate the proposed two-stage vibration suppression and precision pointing platform.
       
  • Investigation of rotating stall in radial vaneless diffusers with
           asymmetric inflow
    • Abstract: Publication date: Available online 13 November 2019Source: Aerospace Science and TechnologyAuthor(s): Chenxing Hu, Ce Yang, Xin Shi, Runnan Zou, Lin Liu, Hua Chen Despite its simple geometry, the turbulent flow in vaneless diffusers is asymmetric and highly skewed. In the present work, a frozen eddy viscosity approach was employed to investigate the instability in a vaneless diffuser with different axial widths. A turbulent stability analysis was performed around the numerically computed mean flows with a non-uniform inflow for both isolated and full-annular vaneless diffusers. The predictions of the flow instability frequency and coherent structure were validated against experimental data. By performing a structural-sensitivity analysis corresponding to the leading eigenvalue, the instability mechanisms for the isolated and full-annular vaneless diffusers were revealed. The sensitivity analysis indicated that the interaction between the boundary layer and the main flow may have been the primary cause of the self-excited instabilities in a narrow diffuser under both axisymmetric and asymmetric inflow. The contribution of the reverse flow near the walls was relatively small. However, the influence of the separation flow near the wall on the instabilities of a wide diffuser was significant, particularly under high-skew inflow conditions. The wavemaker regions were located on the shroud side near the inlet and the hub side near the outlet. When connected to the impeller in the upstream direction, the diffuser outlet backflow was responsible for instability in the diffuser with a radius ratio of 1.53. The jet-wake flow in the diffuser inlet had little impact on the flow instability.
       
  • Analysis of spurious sound due to vortical flow through permeable surfaces
    • Abstract: Publication date: Available online 13 November 2019Source: Aerospace Science and TechnologyAuthor(s): Yijun Mao, Zhiwei Hu Aeroacoustic wave equations proposed by Lighthill and developed by Ffowcs-Williams and Hawkings (FW-H) have been widely used to analyse sound generated from turbulence and its interaction with solid surfaces, such as jet noise and airfoil noise. In engineering applications, the wave equation is usually solved by integral formulations derived by Farassat, where quadrupole volume sources outside permeable integral surfaces are usually ignored in subsonic flow. However, several existing studies have shown that the acoustic prediction result will be greatly contaminated by spurious sources due to vortical components crossing permeable integral surfaces. This paper analytically studies spurious source terms on permeable integral surfaces, and concludes that the convective FW-H equation is always exact to predict the aerodynamic noise because the material derivative and divergence operators in the monopole and dipole sources enable to automatically filter spurious sources located on the permeable integral surfaces. However, the formulations of Farassat fail to filter the spurious sound owing to replacing the spatial derivative by the temporal derivative. A three-dimensional convective frequency-domain version of the Kirchhoff integral formulation is developed to resolve this issue, because it does not use velocity fluctuations as the input variable. Numerical test cases are performed to validate the analytical result and the developed formulation.
       
  • Adaptive Control for Multi-rotor UAVs Autonomous Ship Landing with Mission
           Planning
    • Abstract: Publication date: Available online 13 November 2019Source: Aerospace Science and TechnologyAuthor(s): Kewei Xia, Sangheon Lee, Hungsun Son The autonomous ship landing control issue of multi-rotor Unmanned Aerial Vehicles (UAVs) is investigated. To achieve the ship landing operation efficiently and precisely, a novel mission planning consisting of an approaching stage and a landing stage is first proposed, where the desired altitude for the UAV is provided according to the requirements in each stage. Affected by rough sea wave, a feasible final landing condition is planned such that the UAV could land on the ship board in a safe environment. Then, the solution to the ship landing operation is transformed into the UAV trajectory tracking. Due to the under-actuated nature of the UAV, an adaptive robust hierarchical algorithm is developed such that the position tracking to the desired trajectory and the attitude tracking to the command attitude are achieved. In particular, an asymmetric saturated command force is designed by introducing a dynamic compensator to ensure the nonsingular attitude extraction, and a tracking error constrained applied torque is exploited to avoid the nature singularity of Euler angle in sequence. The asymptotic stability of the closed-loop system is analyzed in view of the hierarchical system stability theory. Simulations are performed to validate the proposed strategy.
       
  • Fuel efficiency improvement on a business jet using a camber morphing
           winglet concept
    • Abstract: Publication date: Available online 12 November 2019Source: Aerospace Science and TechnologyAuthor(s): João Paulo Eguea, Gabriel Pereira Gouveia da Silva, Fernando Martini Catalano International aviation regulations on emissions are becoming more strict. In a scenario where the traditional configuration is reaching maximum efficiency, new technologies may bring further improvement to cope with goals on fuel consumption. Among the new technologies, morphing structures with the capability to adapt their aerodynamic shape for the optimal condition in flight has the potential for aircraft drag and operational fuel consumption reduction. The fixed winglet is usually designed for optimum performance at a single condition, operating in a sub-optimal regime for other parts of the mission. In this work, a genetic algorithm was used to optimize the winglet spanwise camber morphing at different flight phases. Camber variations are based on angle changes in leading and trailing edge sections maintaining a fixed central section for structural feasibility. The camber morphing winglet concept was applied to a midsize business jet and results showed that fuel consumption improvement can be achieved when compared to an optimized fixed geometry winglet.
       
  • Effect of location of a transverse sonic jet on shock augmented mixing in
           a SCRAMJET engine
    • Abstract: Publication date: Available online 12 November 2019Source: Aerospace Science and TechnologyAuthor(s): Vatsalya Sharma, Vinayak Eswaran, Debasis Chakraborty Transverse sonic injection into supersonic cross flow is a well-established technique to inject fuel into a SCRAMJET combustor. A SCRAMJET combustor with a backward facing step acting as a flame-holder has been used for this study. The jet is placed at various locations downstream of the step, where each location represents a distinct flow region. Three-dimensional simulations have been performed using Menter's SST model in our in-house parallel 3-D RANS unstructured grid CFD solver. In such a SCRAMJET configuration, mixing between air and fuel is augmented by shocks generated by the under-expanded jet injected into the supersonic cross flow, hence the jet location is expected to be critical. The performance and mixing of the combustor has been quantified for each of the distinct configurations. The length of the combustor required for complete mixing has also been estimated for the different cases. It is observed that the mixing and performance are strongly affected by the location of the jet in the combustor flow-field. From the results presented in this paper, the optimal location for the jet is somewhat before the end of the recirculation region behind the backward facing step.
       
  • Design and investigation of equal cone-variable Mach number waverider in
           hypersonic flow
    • Abstract: Publication date: Available online 11 November 2019Source: Aerospace Science and TechnologyAuthor(s): Shibin Li, Langquan Li, Wei Huang, Yilong Zhao, Jian Chen A new design idea is put forward to adapt the design requirement of wide-speed range vehicle in the paper. The novel points are that the design Mach number and shock flowfield are variable continuously in the design methodology. The design process is introduced about the wide-speed waverider and the repeatability function is achieved systematically by means of the parameterized modeling. In order to validate the advantages of the new approach during the wide-speed range, the flowfield characteristics are investigated numerically in the paper. The numerical method is validated by comparing the simulation results with wind tunnel experiment data. The obtained results show that the wide-speed range waverider could be obtained easily by the parameterized modeling. For the variable Mach number waverider, the pressure drag accounts for the main part of total drag, about 60∼70%. The percentage of viscous drag increases and that of the rear drag decreases with the increase of flow velocity. The viscous L/D of Case 5 does not change obviously during the wide-speed range. The variable Mach number waverider holds the steady aerodynamic performance during the wide-speed range. This shows that the new design method is very useful for the integrated design of wide-speed hypersonic vehicles.
       
  • Synergetic approach in attitude control of very flexible satellites by
           means of thrusters and PZT devices
    • Abstract: Publication date: Available online 11 November 2019Source: Aerospace Science and TechnologyAuthor(s): Marco Sabatini, Giovanni B. Palmerini, Paolo Gasbarri The interaction between angular motion and flexible vibrations can heavily affect the stability of the spacecraft. Many control strategies have been developed for solving this issue. Some of them are focused on the attitude dynamics while a different approach consists in facing the problem from the structural point of view, trying to actively damp the vibrations induced by the attitude control, using smart material (like piezoelectric) devices.In this research, an approach unifying the two aspects is proposed. The satellite is modeled as a flexible multibody system, in which the two sets of actuators (attitude and structural devices) are commanded by means of a common sliding mode control algorithm. In such a way, the two systems are not considered as competitors (each one trying to cancel the disturbing effects caused by the other one), but they are cooperating for the common goal of acquiring a desired attitude in a given time without residual oscillations. This synergetic approach is first developed in a numerical environment, then it is tested by means of a free-floating platform equipped with flexible appendages, designed and built as a multilayer composite material with a net of embedded PZT patches (sensors and actuators). The overall navigation and control loop is based on the information coming from the Inertial Measurement Unit and from the PZT sensors, which are filtered and sent to the Synergetic controller, with the goal of reaching a desired attitude. The output of the Synergetic controller consists in both the thrusters firing sequence and the PZT actuators voltage difference required to reach the goal. The experimental results are compared with the ones obtained by more classic approaches (attitude and structural control computed independently), commenting both advantages and drawbacks of the different approaches.
       
  • Influence of unmanned combat aerial vehicle agility on short-range aerial
           combat effectiveness
    • Abstract: Publication date: Available online 8 November 2019Source: Aerospace Science and TechnologyAuthor(s): Maolin Wang, Lixin Wang, Ting Yue, Hailiang Liu The flight agility of an unmanned combat aerial vehicle (UCAV) determines its ability to rapidly transition from one state to another. In this paper, the influence of flight agility on short-range aerial combat effectiveness is quantitatively investigated. This research is based on one-on-one three-dimensional aerial combat engagements. First, a 6-DOF mathematical model of the UCAV is established, and a nonlinear dynamic inverse controller is designed. The flight agility is calculated based on the 180∘ flight heading reverse maneuver, and the influence of the control law parameters is studied. To implement autonomous intelligent aerial combat engagements, a three-dimensional approximate dynamic programming method is proposed. The performance of the designed algorithm is validated through both Monte Carlo simulations with various initial conditions and engagements with another algorithm for comparison. After training, the aerial combat simulation framework is constructed by combining the point-mass-based guidance law and a nonlinear UCAV model. Combat engagements are conducted between UCAVs with different configurations. The quantitative results are evaluated through Monte Carlo simulations and correlation analysis.
       
  • Numerical and experimental investigation on the shock mitigation of
           satellite-rocket separation
    • Abstract: Publication date: Available online 8 November 2019Source: Aerospace Science and TechnologyAuthor(s): Jifeng Ding, Hongda Zhao, Jingang Wang, Yi Sun, Zhonggui Chen The shock mitigation technique (SMT) for the satellite-rocket separation has always been one of the hot topics in the field of aerospace. Acoustic Black Hole (ABH) phenomenon which is discovered in recent years refers to the phenomenon of the energy focalization when the stress wave propagates in the plate structure with variable thickness. The ABH and its non-ideal form have received extensive attention and research since they were put forward. Combining the theory of non-ideal ABH with the SMT of satellite-rocket separation, this paper presents a new design of the satellite joint to decrease the satellite-rocket separation shock. At first, the propagation characteristics of stress wave in the thin plate structures with non-ideal ABH are deduced, and the key law affecting the energy attenuation is found. And then, an improved model for the standard satellite joint is proposed, and both the standard and improved models are simplified. What's more, the finite element (FE) models of the simplified satellite joints are established and the shock mitigation (SM) effect is numerically verified with the explicit dynamic code LS-DYNA. At last, the near-field and the whole satellite separation shock experiments are carried out to verify the effectiveness of the SM scheme. The results got in this paper indicate that the SM design based on the non-ideal ABH theory can effectively reduce the satellite-rocket separation shock.
       
  • Experimental and numerical investigations of a scramjet nozzle at various
           operations
    • Abstract: Publication date: Available online 8 November 2019Source: Aerospace Science and TechnologyAuthor(s): Zheng Lv, Jinglei Xu, Kaikai Yu, Guangtao Song The present paper focuses on the study of a scramjet asymmetric nozzle at various operations by applying both experimental and numerical methods, which confirms the reliability of the single expansion ramp nozzle (SERN) design method under geometric constraints based on maximum thrust theory as well. The pitot pressure measurement is used to calibrate the exit Mach number of the facility nozzle. The combination of schlieren photograph, static pressure measurement and strain-gauge balance is employed to obtain the flowfield feature, pressure distribution along the SERN wall and forces acting on the experimental model. Besides, the numerical method is also applied to achieve the more detailed flowfield and performance of the SERN. The results show that the flowfield structure is obviously different between at the experimental conditions and at the actual flight operations. As the interaction of the nozzle plume with the external flow, the shock waves following the expansion waves at the trailing edge of the SERN are all presented at both overexpanded and underexpanded conditions; however, the SERN core flow is independent of the external flow. The existing of two platforms with high-pressure at the front areas of the ramp and cowl are beneficial for improving the thrust performance, verifying the superiority of the new SERN design method. The error of the force between the numerical and experimental results is relatively small, denoting the capability of the numerical method. Furthermore, along with the increase in the flight Mach number, the axial thrust coefficient is decreased, while the lift and pitching moment coefficients are increased. Compared with the cases at the overexpanded operations, the axial thrust loss arising from the underexpanded flow is more serious at certain operations.
       
  • Wake interactions in multibody configurations with different shape
    • Abstract: Publication date: December 2019Source: Aerospace Science and Technology, Volume 95Author(s): Víctor Beltrán, Carlos Méndez, Soledad Le Clainche, José M. Vega This article deals with the low-Reynolds-number wake interaction in two- and three-body configurations, at various angles of attack and various bodies location, cross-section (circular and square cylinders), and diameter. The flow physics is studied using higher order dynamic mode decomposition, which determines the driving frequencies and associated spatial modes of the system. Dependence of such frequencies on the particular multibody configuration is analyzed in detail and compared with the results obtained for related single-body configurations. In particular, it is found that the wake of a multibody configuration exhibits the frequencies of the wakes of the individual isolated bodies. In addition, when the bodies are close to each other, there are new frequencies driving the flow that are related to the whole system of bodies acting as a single entity. The presence of several bodies may lead to the early transition to three-dimensional flow.
       
  • Numerical analysis of fan noise for the NOVA boundary-layer ingestion
           configuration
    • Abstract: Publication date: Available online 7 November 2019Source: Aerospace Science and TechnologyAuthor(s): Gianluca Romani, Qingqing Ye, Francesco Avallone, Daniele Ragni, Damiano Casalino Aim of this paper is to investigate the effects of the turbulent flow developing over a fuselage on fan noise for BLI embedded propulsion systems. Such configurations can suffer from inlet flow distortions and ingestion of turbulence at the fan plane with consequent impact on both broadband and tonal fan noise. The analysis is performed on a modified version of the Low-Noise NASA SDT fan-stage integrated into the ONERA NOVA fuselage in order to reproduce the NOVA BLI configuration. The numerical flow solution is obtained by solving the explicit, transient and compressible lattice-Boltzmann equation implemented in the high-fidelity CFD/CAA solver Simulia PowerFLOW®. The acoustic far-field is computed by using the Ffwocs-Williams & Hawkings integral solution applied to a permeable surface. All simulations are performed for an operating condition representative of a take-off with power cut-back. Installation effects due to the BLI configuration are quantified by comparison with an isolated configuration of the modified Low-Noise SDT fan-stage at the same operating condition. It is found that the BLI fan-stage, which is not optimal, is characterized by strong azimuthal fan blade loading unsteadiness, less axisymmetric and coherent rotor wake tangential velocity variations and higher levels of in-plane velocity fluctuations compared to the isolated engine. This resulted in no distinct tonal components and higher broadband levels in the far-field noise spectra, as well as in an increment of cumulative noise levels up to 18 EPNdB. This study, which represents the first high-fidelity CFD/CAA simulation of a full-scale aircraft geometry comprehensive of a BLI fan/OGV, provides with a clear understanding of the change of the noise sources in BLI integrated configurations.
       
  • Experimental investigation of flow field characteristics in a mixed-flow
           trapped vortex combustor
    • Abstract: Publication date: Available online 6 November 2019Source: Aerospace Science and TechnologyAuthor(s): Ping Jiang, Xiaomin He This paper describes an experimental investigation of flow field characteristics of a conceptual trapped vortex combustor (TVC). It is the first time that the novel TVC is evaluated for turboshaft engine that utilizes a single cavity to provide flame stabilization. A Particle Image Velocimetry (PIV) has been applied to observe the effect of inlet air velocity on the flow field patterns and velocity profiles in a three-dome sector test rig under atmospheric pressure and room temperature. Experiment results show that all average flow fields were stable and self-similar in the cavity in varying operating conditions. A counter-rotating vortex pair was created and safely locked in the cavity along the mainstream plane. As the inlet air velocity increased to 42 m/s, a third vortex was generated. A single dominant stream-wise vortex was spanned the entire cavity along the strut plane. There was a shift in the vortex center location of the strut plane and mainstream plane at the same inlet air velocity, which indicates the three dimensional nature of the flow field in the cavity. Further analysis of velocity profiles showed that flow fields remained stable. The velocity of the vortex downstream zone in the cavity was higher than that in the countercurrent zone.
       
  • Discrete-time incremental backstepping controller for unmanned aircrafts
           subject to actuator constraints
    • Abstract: Publication date: Available online 6 November 2019Source: Aerospace Science and TechnologyAuthor(s): Lijia Cao, Xiaofeng Li, Yu Hu, Mingtao Liu, Jiefu Li In the study, a discrete-time incremental backstepping (DTIBS) controller is proposed for the aircrafts with unknown actuator dynamics. Taylor series and approximating discretization approach are used, and thus the second-order continuous-time nonlinear system is modified as a discrete-time nonlinear plant in which input is in an incremental form. The incremental control laws are designed by using the incremental nonlinear dynamic inversion (INDI) approach and time-delayed control (TDC) method incorporating the robust terms by applying a standard gradient-based adaption method and the chain-rule. The TDC is introduced to design the control law, and thus concrete prior knowledge of the control effectiveness matrix involving a few unknown aerodynamic coefficients is not required. Furthermore, the stable linear filters in the discrete-time form are designed to compensate for the filtered errors and actuator dynamics. A comparison of the numerical simulation results verifies that DTIBS with the robust terms can significantly improve tracking performance. Root mean square error of the whole tracking process (RMSEOTP) is defined to demonstrate the high tracking accuracy of the controller.
       
  • Low speed longitudinal aerodynamic, static stability and performance
           analysis of a hypersonic waverider
    • Abstract: Publication date: Available online 6 November 2019Source: Aerospace Science and TechnologyAuthor(s): Tamas Bykerk, Dries Verstraete, Johan Steelant Hypersonic waveriders have the potential to significantly reduce travel times on long haul civilian transport routes. The design of hypersonic aircraft is heavily influenced by the aerodynamic efficiency at the cruise Mach number, resulting in less than ideal geometries for subsonic flight. Waverider aerodynamics and stability in the low speed regime is rarely investigated and not well understood, but is crucial for horizontal take-offs and landings. This paper presents a combination of numerical simulation results and experimental data for the low speed variant of the Mach 8 HEXAFLY-INT waverider. Aerodynamic, control and stability testing was conducted in the University of Sydney 4 foot by 3 foot low speed facility, while propulsion testing of the vehicle-integrated electric ducted fan was completed in the 7 foot by 5 foot tunnel. Motor thrust settings were tested for 8 lithium polymer cells connected serially drawing between 5 and 25 amperes. Computational fluid dynamics simulations are compared with wind tunnel tests for angles of attack between −5 and 25 degrees and elevon deflections between −10 and 10 degrees. Results show the aerodynamics is dominated by leading edge flow separation and vortex lift. At a centre of gravity location of 44.4% of the vehicle length, stability is observed up to 22 degrees angle of attack. Past this point, instability occurs due to vortex breakdown. The centre of gravity aft stability limit was found at 53.1% of the vehicle length. Overall, good agreement is seen between simulation and tunnel data, validating the modelling methods used. The low speed demonstrator can achieve trimmed flight from 12 m/s, but is only speed stable above 19 m/s. A cruise speed of 19 m/s is selected and can be attained with approximately −9.2 degrees of elevon and 7.1 degrees AoA for a centre of gravity location of 44.4%. Shifting the centre of gravity aft can reduce the trim angle of attack to below 6 degrees with −4 degrees elevon deflection. Take-off and landing can be achieved at 15 m/s between 9.8 and 12 degrees angle of attack, depending on centre of gravity configuration. A maximum climb rate of 2.1 m/s is predicted at 16.3 m/s based on the power settings tested. Overall, the results show the aircraft satisfies stability and performance requirements in the longitudinal axis.
       
  • Experimental study on enhancement of supersonic twin-jet mixing by vortex
           generators
    • Abstract: Publication date: Available online 5 November 2019Source: Aerospace Science and TechnologyAuthor(s): Aqib Khan, Saif Akram, Rakesh Kumar Experimental results on the mean flow evolution and the control of single and twin compressible jets at Mach 1.6 are presented. The jets issue from conical CD nozzles closely placed side-by-side resembling the twin nozzle configuration of supersonic aircrafts. The results are relevant to scenarios where turbulent jet mixing, supersonic core length, thermal radiation and acoustic loading are of concern. Experiments show that closely spaced twin jets grow, merge and interact near the inter-nozzle region that influences the characteristic decay and jet spread. Moreover, the deviation in centerline characteristic decay is more significant at off-design conditions. Vortex generators in the form of small metallic rectangular tabs mounted at the nozzle exit plane in different azimuthal orientations are used to control the mixing characteristics and the spread of these jets. Abrupt reduction in the core length and suppression of shock cell structure is achieved in over to under-expanded conditions. Furthermore, the orientation of vortex generators is found to significantly influence the development of jet flow field. The jet bifurcation and formation of daughter streams with distorted quasi-periodic shock cells structure are visualized using the schlieren technique. The underlying mechanisms for the observed effects and the behavior of daughter streams are discussed.
       
  • Adaptive fault-tolerant attitude tracking control of hypersonic vehicle
           subject to unexpected centroid-shift and state constraints
    • Abstract: Publication date: Available online 4 November 2019Source: Aerospace Science and TechnologyAuthor(s): Yizhen Meng, Bin Jiang, Ruiyun Qi This paper presents a study on hypersonic vehicle (HSV) with unexpected centroid shift, actuator fault, system input saturation and state constraints, aiming to investigate the adaptive fault-tolerant control method for stability recovery of HSV. By analysis, the influence of unexpected centroid shift mainly reflects in three aspects: 1) uncertainties of the system, 2) eccentric moments, 3) variation of system inertial matrix. For system uncertainties, eccentric moments and actuator fault, the radial basis function neural network (RBFNN) and adaptive estimator are utilized to obtain those unknown nonlinearities. For the bad effects of actuator faults, system input constraints and variation of inertial matrix, an adaptive estimator combined with Nussbaum gain is designed to cope with that problem. In addition, the barrier Lyapunov function is adopted in order to limit the amplitude of the attitude angles ensuring the safety of HSV. Then, the fault-tolerant controller is established using the backstepping technology to synthesize various control strategies. At last, the boundedness of whole closed-loop system signals and stability of system are demonstrated by Lyapunov theory of stability. The simulation results illustrate the effectiveness of the proposed control strategies in this paper.
       
  • Reconfigurable Mission Plans for RPAS
    • Abstract: Publication date: Available online 4 November 2019Source: Aerospace Science and TechnologyAuthor(s): Hector Usach, Juan A. Vila This paper deals with the problem of formally defining and specifying Mission Plans for Remotely Piloted Aircraft Systems (RPAS). Firstly, the profile of RPAS missions is highly variable and different from those of commercial flights. Route variability from the planned route is frequent due to operating conditions and, especially, contingencies. For this reason, RPAS Mission Plans should be reconfigurable: they should allow the nominal plan to be modified during flight time. Secondly, aviation authorities may require the ability to operate in an autonomous mode in response to Command and Control (C2) link losses. As a result, RPAS Mission Plans should specify all possible routings and behaviors in greater detail. The Reconfigurable Mission Plan concept introduced in this paper expands on current flight plans by providing a level of description that improves predictability and allows for reconfiguration, contingency handling, and higher levels of automation and pilot assistance. The paper presents a detailed discussion of RPAS contingency handling and develops a formal specification of the Reconfigurable Mission Plan concept. The paper also develops algorithms for dynamically configuring Mission Plan routes that might mitigate the effect of contingencies. Finally, the whole proposal is validated with a prototype implementation and a proof of concept.
       
  • Guidance strategies for interceptor against active defense spacecraft in
           two-on-two engagement
    • Abstract: Publication date: Available online 4 November 2019Source: Aerospace Science and TechnologyAuthor(s): Haizhao Liang, Jianying Wang, Jiaqi Liu, Peng Liu This paper investigates the guidance problem for interceptors against spacecraft with active defense in a two-on-two engagement. There are four adversaries in the engagement which are interceptor, protector, spacecraft and active defender. The interceptor is required to capture the spacecraft and evade the defender with the assist of the protector. Two classes of guidance laws are proposed based on norm differential game strategy and linear quadratic differential game strategy, respectively. Interceptor using norm differential game guidance laws is able to pursue the spacecraft without being intercepted by defender, even though the maneuverability of both interceptor and protector is lower than defender. Additionally, linear quadratic differential game guidance laws derived by numerical solution of Riccati differential equation take into account the control saturation, fuel cost and chattering phenomenon simultaneously. Finally, the effectiveness and performance of the developed guidance approaches are demonstrated by nonlinear numerical simulations.
       
  • On the use of thermally perfect gas model for heating prediction of
           laminar and turbulent SWBLI
    • Abstract: Publication date: December 2019Source: Aerospace Science and Technology, Volume 95Author(s): Zhenhua Jiang, Chao Yan The model of thermally perfect gas has been investigated in the heating prediction of laminar and turbulent shock wave boundary layer interaction (SWBLI) flows. The method of the polynomial curve fit coupling to thermodynamics equation is examined for higher temperature range. The characteristic weighted essentially non-oscillatory (WENO) scheme is utilized to capture the complex flow details and meantime stabilize the strong shocks in the SWBLI flows. Both the laminar and turbulent, steady and unsteady test cases are carried out to assess the performance of the designed method. Numerical results have substantiated the thermally perfect gas model as an effective model in the challenging SWBLI heating predictions in comparison with the existing model of calorically perfect gas.
       
  • A flow model for tip leakage flow in turbomachinery using a square duct
           with a longitudinal slit
    • Abstract: Publication date: December 2019Source: Aerospace Science and Technology, Volume 95Author(s): Yanfei Gao, Yangwei Liu A physical flow model to simulate the tip leakage flow (TLF) is proposed, in order to reproduce the jet flow/main flow shear mechanism of tip leakage vortex (TLV) roll-up in turbomachinery. The model is a main flow in a square duct with a jet flow from a longitudinal slit on the top, which could simplify the flow conditions for numerical simulations and experiments. The interaction of jet flow/main flow generates a streamwise vortex, resembling the TLV. The flow model is simulated using large-eddy simulation (LES) and compared with the measurements of a prototype rotor. The geometric parameters and boundary conditions are abstracted from the prototype rotor for verification. It is found that the flow model could generate similar flow field and turbulence structures to the prototype TLF, therefore it can be used to assess the turbulence models in practical flows. A RANS simulation under the same condition is also carried out, which shows the defect of current turbulence models. LES of a low-Reynolds number case indicates that the flow model could reproduce the TLF structures under various Reynolds number conditions, indicating that direct numerical simulation could also be applied to the investigation of the TLF model, thus the proposed model has the potential as a standard model for TLF research.
       
  • Road map to L 4/L 5 with a solar
           sail
    • Abstract: Publication date: December 2019Source: Aerospace Science and Technology, Volume 95Author(s): Ariadna Farrés, Jeannette Heiligers, Narcís Miguel This paper explores the capability of solar sails to transfer a probe from the displaced Sun-Earth L1 and L2 libration points to the region of practical stability (RPS) around the triangular equilibrium points L4 and L5. If the sailcraft arrives inside the RPS with zero synodical velocity, it will remain there with minor station keeping requirements. Moreover, the location of the RPS is ideal for space weather missions as the Sun can be observed from a different angle compared to spacecraft orbiting the L1 point. The unstable manifolds of the displaced L1 and L2 points come close to these regions providing opportunities for natural transfer trajectories. By varying the solar sail orientation along the manifold, the dynamics can be altered and simple transfer trajectories that reach the RPS with few sail maneuvers are enabled. However, these trajectories are not optimal from a transfer time perspective, but can serve as suitable initial guesses for a direct optimization method to find minimum-time transfers between the displaced L1 and L2 points and the RPS at L4 and L5.
       
  • Fixed-time integral-type sliding mode control for the quadrotor UAV
           attitude stabilization under actuator failures
    • Abstract: Publication date: December 2019Source: Aerospace Science and Technology, Volume 95Author(s): Wenquan Gong, Bo Li, Yongsheng Yang, Hanyu Ban, Bing Xiao In this work, two fixed-time fault-tolerant control schemes are developed to address the problem of attitude stabilization of a quadrotor unmanned aerial vehicle with external disturbances and actuator faults. By utilizing homogeneous approach, a nominal controller is first presented to ensure the fixed-time stability of the fault-free system. Then, a novel integral-type sliding mode and adaptive technique based fixed-time control law is proposed to restrain the disturbances and actuator faults. To further compensate the uncertainties and failures actively, a fixed-time observer based fixed-time fault-tolerant controller is proposed using the integral-type sliding mode control strategy as well. The proposed schemes are proved to be stable theoretically and strictly in the sense of Lyapunov. Finally, the fine performances and capabilities of the designed schemes are verified by numerical simulations.
       
  • Investigation of rotating detonation fueled by the pre-combustion cracked
           kerosene
    • Abstract: Publication date: December 2019Source: Aerospace Science and Technology, Volume 95Author(s): Yepan Zhong, Yun Wu, Di Jin, Xin Chen, Xingkui Yang, Shunli Wang In this study, a method of pre-combustion cracking is adopted in the investigation of the rotating detonation fueled by kerosene. The basic characteristics of the rotating detonation wave (RDW) including the wave speed, pressure, and propagating modes are researched. The wave speed increases when the equivalence ratio is near the stoichiometric ratio, but it is little affected by the flow rates. Different to the wave speed performance, the pressure of the RDW tends to increase when the flow rates rise but show weak relation with the ER. Features and transition of the five rotating detonation modes including the two-co rotating waves, two-counter rotating waves, single-wave, pop-out and failure mode are investigated. The lean fuel boundary of the RDW is broadened with the increase of the flow rates. Also, the effect of the oxygen ratio (50% and 30%) of the oxidizer (oxygen-enriched air) on the characteristics of the RDW is investigated. The rotating detonation using oxidizer with the higher oxygen ratio has a better speed performance than with the lower oxygen ratio.
       
  • Mechanics of a novel cellular structure for morphing applications
    • Abstract: Publication date: December 2019Source: Aerospace Science and Technology, Volume 95Author(s): Weidong Liu, Honglin Li, Zhendong Yang, Jiong Zhang, Cenbo Xiong Cellular structures could obtain mechanical properties that are inaccessible with ordinary materials. A novel zero Poisson's ratio cellular structure with low in-plane moduli and great morphing capabilities for multiple in-plane morphing is proposed in this paper. Theoretical models of the elastic constants of the structure are established and verified by the finite element method. Results show that the equivalent moduli of the structure are several orders of magnitude lower and the maximum global strains are considerably larger than those of the raw material. Meanwhile, the mechanical properties possess large changing ranges under the variations of parameters. Comparisons between the proposed structure and two existing ones indicated that the proposed structure possesses better performance and larger range of material selection for in-plane tensile morphing, while with some drawbacks for the in-plane shear morphing. The proposed structure shows great potential as core for flexible skin or flexible structure for multiple in-plane morphing applications.
       
  • Radar/infrared integrated stealth optimization design of helicopter engine
           intake and exhaust system
    • Abstract: Publication date: December 2019Source: Aerospace Science and Technology, Volume 95Author(s): Zeyang Zhou, Jun Huang, Jinjun Wang Along with the diversification and sophisticated development of detection methods in modern warfare, helicopters are increasingly subject to unilateral or simultaneous threats from radar and infrared detectors. In order to improve the survivability and operational effectiveness of the helicopter, a comprehensive stealth approach based on Pareto solution is presented. Considering the geometric constraints and aerodynamic characteristics of the engine intake and exhaust system, the model of the system is established by the full factorial design, the internal, central and external flow fields are constructed, then the high-precision computational fluid dynamics method is used to simulate the total flow field under the rotor downwash airflow in hovering state. The radar cross section of the system is evaluated by the physical optics and physical theory of diffraction. Based on the Monte Carlo and ray tracking method, the infrared signature of the system is calculated and analyzed in detail. Under the comprehensive evaluation and selection of comprehensive stealth approach, the optimization model of the system is continuously established and updated. The ultimate design has achieved good results in both radar cross section reduction and infrared radiation suppression and the proposed method is effective and efficient for radar/infrared integrated stealth of helicopter engine intake and exhaust systems.
       
  • Effect of the fuel-air flow velocity on heat release rate of swirling
           non-premixed methane flames
    • Abstract: Publication date: December 2019Source: Aerospace Science and Technology, Volume 95Author(s): Kuanliang Wang, Fei Li, Pengfei Zou, Xin Lin, Ronghai Mao, Xilong Yu A laboratory-scale gas turbine model combustor fueled with methane is studied experimentally with the aid of three-dimensional computed tomography of chemiluminescence (3D-CTC) and high speed (5 kHz) chemiluminescence imaging. Various fuel-lean operating conditions were tested to investigate the impact of flow velocity on heat release rate oscillation and spatial structure transition with fixed global equivalence ratio of about 0.65 and dump plane velocity of 2.9–18.3 m/s. In the study of combustion structure transition, the three-dimensional relative emissions of CH* were measured and taken as qualitative indicators of the heat release rate. This 3D measurement method utilizes CH* images from 8 directional as inputs combined with tomographic algorithms to compute the 3D distribution of CH* CL intensities. For all tested conditions, pronounced extension of inner recirculation zone (IRZ) along the nozzle is observed under the attached (V-shaped) swirl stabilized flames. During the increase of Reynolds number, the heat release zone changing obviously along the nozzle radial and axis direction, and the largest heat release plane moves downstream significantly. In addition, an intensified high-speed camera was adopted for the heat release dynamics study. Strong oscillations appeared in the flame zone that significantly affected the total heat release oscillations, and oscillation increases with the raise of Reynolds number.
       
  • Optimum aerodynamic shape design under uncertainty by utility theory and
           metamodeling
    • Abstract: Publication date: December 2019Source: Aerospace Science and Technology, Volume 95Author(s): Xiaosong Du, Leifur Leifsson In this work, utility theory is introduced to optimum aerodynamic shape design under uncertainty (also called robust aerodynamic design). Specifically, utility theory is used to formulate the objective function of the optimization problem. The advantage of the proposed approach over the commonly used weighted sum method is that it does not require the use of weighting factors or the addition of constraints on the statistical moments. The polynomial chaos expansion metamodel with the least-angle regression and the hyperbolic truncation scheme are used to accelerate the uncertainty propagation and the optimization process. The proposed approach is demonstrated on the optimum airfoil shape design under uncertainty at steady transonic conditions. Two design cases are considered. In both cases the drag coefficient is to be minimized subject to constraints on the lift coefficient and the airfoil thickness at two chordwise locations. The first case treats the Mach number as uncertainty parameter and the second case treats the Mach number and the lift coefficient at target as uncertain. The proposed method is compared with deterministic single-point optimization and multi-point optimization, and the standard robust design formulations. Results show that the proposed approach is capable of obtaining airfoil design of the lowest mean drag coefficient with the smallest standard deviation as compared to the other approaches. In the first case, the proposed approach yields a design with a mean drag coefficient comparable to the standard robust design (around 97.6 drag counts, cts), but with a significantly lower variance (0.6 cts versus 2.5 cts). In the second case, the proposed approach yielded a design with a higher mean drag coefficient than the standard approach (98.4 cts versus 97.6 cts), but with a lower standard deviation (4.1 cts versus 4.8 cts). In both cases, the deterministic approaches yield designs with comparable or lower drag coefficients but with significantly larger standard deviations.
       
  • Vibration analysis of rotating functionally graded tapered beams with
           hollow circular cross-section
    • Abstract: Publication date: December 2019Source: Aerospace Science and Technology, Volume 95Author(s): Shipeng Dong, Liang Li, Dingguo Zhang The dynamic modeling and free vibrations of rotating functionally graded (FG) tapered cantilever beams with hollow circular cross-section are studied in this paper. To capture the additional dynamic stiffening terms, the axial shrinkage of the beam caused by the transverse displacement is considered. The dynamic equations of the system governing stretching motion, flapwise bending motion, and chordwise bending motion are derived via employing assumed modes method and Lagrange's equations. Based on the first order approximate coupling (FOAC) dynamic model, natural frequencies and mode shapes of the beam system are calculated by solving eigenvalue problem of the deduced dimensionless vibration equations. Influences of the angular speed, the hub radius, the slenderness ratio, the ratio of hollow radius to the root radius, the taper ratio, and the functional gradient index on natural frequencies are studied. Frequency veering and mode shape interaction are discussed when the bending-stretching mode coupling effect of the beam is considered.
       
  • Output feedback control for aircraft at high angle of attack based upon
           fixed-time extended state observer
    • Abstract: Publication date: December 2019Source: Aerospace Science and Technology, Volume 95Author(s): Junjie Liu, Mingwei Sun, Zengqiang Chen, Qinglin Sun This paper presents a novel fixed-time extended state observer (FXTESO)-based fixed-time output feedback control scheme for aircraft with thrust vector at high angle of attack. In order to enhance the robustness of the closed-loop control system, a FXTESO is designed to estimate and compensate model uncertainties, external disturbance and the strong coupling among different channels. Furthermore, theoretical analysis shows that the convergence time of FXTESO is independent of initial estimation errors. For the double integrator systems obtained by FXTESO feedback linearization, a continuous output feedback control is utilized to obtain expected performance and fixed-time stability. The stability analysis for the closed-loop aircraft control system is conducted by Lyapunov theory. The daisy chain method is adopted to realize the control allocation. Finally, several numerical simulations are provided to demonstrate the effectiveness and robustness of the proposed methodology.
       
  • Distributed cooperative encirclement hunting guidance for multiple flight
           vehicles system
    • Abstract: Publication date: December 2019Source: Aerospace Science and Technology, Volume 95Author(s): Jianglong Yu, Xiwang Dong, Qingdong Li, Zhang Ren Distributed cooperative encirclement hunting guidance strategy design and analysis issues for multiple flight vehicles system against a maneuvering target are considered in this paper. Distinct from the former results, the cooperative encirclement hunting guidance laws are based on the leader-follower coordination structure, and are divided into two parts. Firstly, for the leader flight vehicle, a full-head-on interception guidance law is proposed against the maneuvering target, where the uncertain dynamics and the target's unknown maneuver are estimated and compensated by using an extended state observer. For the follower flight vehicles, the distributed time-varying encirclement hunting line of sight angle formation tracking laws with overload saturation are designed where distributed extended state observers are introduced to approximate the complicated uncertain items and the leader vehicle's input signals. Then, the design processes of cooperative encirclement hunting guidance laws are summarized within five steps as an algorithm. Thirdly, the stability and the properties of the proposed cooperative encirclement hunting guidance algorithm are analyzed by employing Lyapunov theories. Finally, numerical simulation results illustrate the effectiveness of achieved cooperative encirclement hunting guidance strategies.
       
  • Buzz flow diversity in a supersonic inlet ingesting strong shear layers
    • Abstract: Publication date: December 2019Source: Aerospace Science and Technology, Volume 95Author(s): Hao Chen, Hui-jun Tan To further explore the shear-layer-induced buzz diversity recently discovered in an overspeed supersonic inlet, an external-compression supersonic inlet is specially designed and carefully studied through wind-tunnel test at its design Mach number of 2.0. It is observed that the flow instability begins with the little buzz mode featuring a stable terminal shock and a lightly unsteady shock-induced separation bubble. Then a combination of another two stronger buzz styles replaces the little buzz. Of them the medium buzz is characterized by a locally destabilized terminal shock and the varying cowl-side reverse flow, whereas the big buzz is distinguished by intense separation unsteadiness. Interestingly, the medium buzz cannot stay long and vanishes eventually. Instead of an ordinary buzz case in the design Mach number situation, current buzz flows are found pretty similar to the overspeed inlet case superficially and fundamentally under the influence of two strong shear layers, albeit with a clear difference in the duration of the medium buzz. Accordingly, the possibility of buzz flow diversity and the related shear-layer effect proposed recently get further supported. Besides, it is indicated that the overspeed operation is not the only situation allowing for the diversified inlet buzz.
       
  • Byrnes-Isidori-based dynamic sliding-mode control for nonminimum phase
           hypersonic vehicles
    • Abstract: Publication date: December 2019Source: Aerospace Science and Technology, Volume 95Author(s): Yuxiao Wang, Tao Chao, Songyan Wang, Ming Yang This paper deals with the dynamic sliding-mode (DSM) control problem for nonminimum phase hypersonic vehicles (HSVs). When the elevator is the only control surface available for the altitude dynamics, the HSV model exhibits unstable zero dynamics, preventing the application of standard inversion-based control techniques. To solve this problem, a DSM control method based on Byrnes-Isidori (B-I) normalized form is proposed, achieving asymptotic tracking of velocity and Flight-Path-Angel (FPA) while stabilizing internal dynamics. First, for the pitch dynamics with nonminimum phase behavior, external dynamics and internal dynamics are determined by coordinate transformation to convert the longitudinal model to B-I normalized form, based on which a criterion of nonminimum phase property is given by the stability analysis of internal dynamics. Then, a DSM control method is proposed for the FPA subsystem of nonminimum phase, which transforms the output tracking problem into stabilization problem of an augmented system consisting of internal dynamics and dynamic compensator, making closed-loop pole adjustable, and thus improves the tracking performance. The principle of parameters determination is proposed, which is proved to achieve the stability of the system on the sliding surface. Besides, nonlinear disturbance observer is utilized to compensate the error caused by dynamic inversion control. The proposed method is compared with approximate backstepping control and is shown to have superior tracking accuracy as well as robustness from the simulation results. This paper may also provide a beneficial guidance for control design of other complex systems of nonminimum phase.
       
  • The lateral control during aircraft-on-ground deceleration phases
    • Abstract: Publication date: December 2019Source: Aerospace Science and Technology, Volume 95Author(s): Yaqi Dai, Jian Song, Liangyao Yu, Zhenghong Lu, Sheng Zheng, Fei Li Lateral control during aircraft-on-ground deceleration, which is one of the most important issues in aircraft-on-ground maneuvers, is discussed in this paper. Based on linear quadratic and predictive control theories, two controllers are developed to replace pilot control, which is effective only to a limited level under severe conditions. Particularly, because the aircraft forward speed decreases during deceleration, we propose a novel weighted model predictive control (MPC) method to control this parameter-varying system. Under the same severe conditions, simulation results show different efficiencies for these two controllers and both exhibited better performance than pilot control.
       
  • Editorial foreword of the special issue of the 8th International
           Conference on Vortex Flow Mechanics (ICVFM2018)
    • Abstract: Publication date: Available online 18 October 2019Source: Aerospace Science and TechnologyAuthor(s): Bin Chen, Zhifu Zhou, Panidis Thrassos, John A. Ekaterinaris
       
  • Simplified numerical simulation model for hydroxyl ammonium nitrate-based
           monopropellant rocket engines
    • Abstract: Publication date: Available online 14 October 2019Source: Aerospace Science and TechnologyAuthor(s): De-chuan Sun, Wei-bin Xiang A simplified model is proposed to simulate the working process of hydroxyl ammonium nitrate-based monopropellant rocket engines. The porous medium model and volume-of-fluid model are used to solve for the internal flow field of a monopropellant engine containing a catalyst bed to emphasize the establishment of a propellant decomposition model. The decomposition process is assumed to be separable into mass transfer and quick energy release processes. The mass transfer process is described by a two-stage decomposition model that combines catalytic and thermal decompositions according to temperature. This paper explains how to implement the two-stage decomposition model by using a titration experiment and thermal decomposition data. A detailed example is provided involving the calculation of the steady-state flow field of a 150-N monopropellant rocket engine in FLUENT. The results obtained using only the catalytic decomposition model and the two-stage decomposition model were compared with those of hot-fire tests, and show that the two-stage decomposition model is accurate. The combustion chamber pressure obtained from two- and three-dimensional simulations for the flow field of the engine agreed with the results of hot-fire tests. The calculated external wall temperature of the lower catalyst bed was slightly higher than the measured temperature, whereas the external wall temperature of the upper catalyst bed was close to the measured values.
       
  • Effect of turbulence modeling for the prediction of flow and heat transfer
           in rotorcraft avionics bay
    • Abstract: Publication date: December 2019Source: Aerospace Science and Technology, Volume 95Author(s): Altug Akin, Harika S. Kahveci In this paper, four turbulence models are compared on the basis of the predictions they produce for the flow and heat transfer in the avionics bay area of a rotorcraft. The turbulence models studied are the standard k-ε, Renormalization Group (RNG) k-ε, realizable k-ε, and Shear-Stress Transport (SST) k-ω model. The avionics bay used in the study houses avionics equipment mounted on the floor and on a rack inside the bay to mimic a realistic distribution of equipment in actual rotorcraft. The avionics bay incorporates a cooling system consisting of a fan that intakes ambient air via a forced-convection method and an exhaust, with the purpose of keeping the avionics equipment temperatures below their operational limits. The turbulence levels, flow and thermal fields are investigated and compared in order to quantify the differences between the predictions of the turbulence models used in computations. It is observed that the use of the standard and realizable k-ε models mostly produce similar flow and thermal results across the bay area, while the largest differences between the predictions are found with the RNG k-ε and the SST k-ω turbulence models especially at the locations in the vicinity of the fan impingement. Comparing the avionics equipment surface temperature predictions, the standard and realizable k-ε turbulence models are observed to produce slightly more conservative results. The average variation between the surface temperature predictions by all models is less than 3.5 K, indicating that this parameter is considerably insensitive to the selected turbulence model. A close examination of the fan jet region starting from the fan inlet revealed generally similar predictions of flow and thermal features by all turbulence models. The maximum variation in the velocity and temperature predicted by all turbulence models is 2.2% and 0.1% of the fan inlet conditions, respectively. Large differences in turbulence intensity were observed depending on the location downstream of the fan jet and the turbulence model used.
       
  • Adaptive path following control of a stratospheric airship with full-state
           constraint and actuator saturation
    • Abstract: Publication date: December 2019Source: Aerospace Science and Technology, Volume 95Author(s): Tian Chen, Ming Zhu, Zewei Zheng In this paper, the path following problem is addressed for a stratospheric airship subject to full-state constraint, input saturation and external disturbances. A novel full-state constrained path-following algorithm, which ensures that all states of the system remain in the predetermined intervals, is proposed based on the theories of barrier Lyapunov function, vector field guidance, adaptive backstepping control and saturation compensator. Firstly, an error-constrained vector field (ECVF) guidance law is presented to handle the position tracking error, which can navigate the stratospheric airship along the predefined path and guarantee that the error is limited by the time-varying asymmetric constraints. Secondly, a state-constrained adaptive attitude controller is introduced to track the desired attitude calculated by the ECVF, in which a saturation compensator of virtual control law is employed to handle the problem of angular velocity constraint. Finally, a state-constrained adaptive velocity controller is designed to maintain an appropriate scheduled velocity. Furthermore, two auxiliary design systems are used to deal with the actuator saturation problem, and adaptive laws are developed for handling dynamic couplings and unknown disturbances. Stability analysis implies that all signals in the closed-loop system are uniformly ultimately bounded, and all path-following state constraint requirements are never violated. Meanwhile, the effectiveness of the proposed control algorithm is demonstrated by comparative simulation results.
       
  • SPH-FEM simulation of impacted composite laminates with different layups
    • Abstract: Publication date: Available online 11 October 2019Source: Aerospace Science and TechnologyAuthor(s): Yadong Zhou, Youchao Sun, Tianlin Huang, Wenchao Cai Composite laminates offer the potential for reducing the weight of civil aircrafts. However, a major hazard to civil aviation is bird-strike impact damage. In this paper, bird-strike impact damages of composite laminates are numerically investigated by means of Smoothed Particle Hydrodynamics (SPH) and finite element method (FEM) analysis. We mainly focus the influence of laminates' layups on damage modes and energy variations of bird impact on a square laminated plate. The SPH method and an equation of state were employed for the bird projectile. A Continuum Damage Mechanics approach in FEM was applied to simulate failure initiation and damage evolution in composite laminates. Damage maps were calculated with respect to three different layups, i.e. 8 plies, 16 plies and 24 plies, indicating localized damage area as the ply number increased. Deformations of laminates and projectile were studied during the impact damage process. The energy variations (kinetic, strain and damage dissipations) were also comparatively investigated. Results can serve as design guideline in future bird-strike study of composite laminates in complex aircraft structures.
       
  • Decomposed-coordinated surrogate modeling strategy for compound function
           approximation in a turbine-blisk reliability evaluation
    • Abstract: Publication date: Available online 11 October 2019Source: Aerospace Science and TechnologyAuthor(s): Cheng-Wei Fei, Cheng Lu, Rhea P. Liem Performing probabilistic analyses on a complex structure is challenging with a high computational burden, owing to the many components and multiple disciplines involved, with high nonlinearity and many hyperparameters. Despite the advancements in surrogate models, they are still insufficient to accurately model compound functions with many sub-layers and sub-functions. In this paper, we propose the decomposed-coordinated surrogate model method (DCSMM) to improve the modeling accuracy and efficiency of compound functions. This improvement will enable performing expensive probabilistic analyses, which typically involve thousands of Monte Carlo simulation runs, efficiently. This type of analysis would be too computationally expensive to perform when using full-scaled models. The proposed DCSMM uses the decomposition and coordination strategy, and combines it with surrogate modeling methods. In this work, we establish the mathematical model of the DCSMM with quadratic polynomial (QP) and Kriging model, and develop QP-DCSMM (the DCSMM based on QP), K-DCSMM (the DCSMM based on Kriging) and M-DCSMM (the DCSMM based on the mixture of QP and Kriging). The approximation accuracy and simulation performance (including computational precision and efficiency) of the DCSMM are demonstrated with an analytical model and a turbine blisk multi-failure modes of an aeroengine as an engineering case study. The proposed DCSMM is demonstrated to be effective in modeling the high-nonlinearity between output response and input variables, in addition to being robust. These benefits become even more prominent as we increase the number of Monte Carlo simulation runs. Overall, this study shows a high-efficiency and high-precision approximation method for complex compound functions and complex structures. This contribution will further enrich the theory and application of probabilistic statistical analysis as well. This paper also offers useful insights into engineering optimization and reliability design pertaining to multi-model mechanical systems.
       
  • Dynamic probability modeling-based aircraft structural health monitoring
           framework under time-varying conditions: Validation in an in-flight test
           simulated on ground
    • Abstract: Publication date: Available online 11 October 2019Source: Aerospace Science and TechnologyAuthor(s): Fang Fang, Lei Qiu, Shenfang Yuan, Yuanqiang Ren This paper proposes a dynamic probability modeling-based aircraft Structural Health Monitoring (SHM) framework which provides a modular hierarchical SHM architecture for the development of applicable aircraft SHM techniques. The problem of reliable damage monitoring under time-varying conditions, which is the main application obstacle, is fully considered in the framework by the double probability models combined with the short term and long term dynamic update of the models. To realize the SHM capability of the framework, an adaptive constructing method of Gaussian mixture model is proposed for stable and efficient probability modeling and the probability similarity between dynamically updated models is measured for normalized damage detection. The framework is realized by combining with the guided wave SHM technique and validated in a full-scale aircraft fatigue test which is an in-flight test simulated on ground. The cracks of the right landing gear spar and the left wing panel on the aircraft structure are monitored reliably under the fatigue load conditions.
       
  • Modeling and analysis for integrated airframe/propulsion control of
           vehicles during mode transition of over-under Turbine-Based-Combined-Cycle
           engines
    • Abstract: Publication date: Available online 10 October 2019Source: Aerospace Science and TechnologyAuthor(s): Jialin Zheng, Juntao Chang, Jicheng Ma, Daren Yu Mode transition control is a critical issue of Turbine-Based-Combined Cycle (TBCC) engines when the primary thrust provider changes from gas turbine engines to ramjets/scramjets. Improper control laws might incur unexpected propulsion performance and even lead to mission abortion. Existed control laws are designed from the perspective of the combined engine itself without aerodynamic/propulsive couplings considered. However, like scramjet-powered aircraft, those with TBCC engines propelled also have intricate couplings between the engine and the airframe, especially during TBCC mode transition. In this paper, a nonlinear longitudinal TBCC-powered dynamic vehicle model is derived from first principles with extra aerodynamic effects and adjustable surfaces involved when a typical TBCC engine is integrated into the airframe. Then, a control-oriented model with six control inputs is obtained by approximately expressing aerodynamic coefficients through curve-fitting methods. Trim results indicate that the total thrust required to maintain a steady flight increases at different steady stages during mode transition of the TBCC engine. One feasible control law is designed with dynamics of the integrated system considered for a typical mode transition process to reveal a way that control inputs should be regulated to maintain a steady flight during mode transition of the TBCC engine.
       
  • Secondary buckling and failure behaviors of composite sandwich panels with
           weak and strong cores under in-plane shear loading
    • Abstract: Publication date: Available online 10 October 2019Source: Aerospace Science and TechnologyAuthor(s): Dong Li, Bao-Zong Huang The secondary buckling and failure behaviors of composite sandwich panels (CSPs) subjected to in-plane shear loading are studied via a self-developed quasi-conforming finite element method. The influences of key material and geometry parameters on postbuckling and failure behaviors are investigated. Numerical results show that (1) postbuckling failure is dominated by the ratio of two strengths, i.e. the through-thickness shear strength of the core and the transverse tensile strength of the lamina. In addition, two constant thresholds for this strength ratio exist in the relationship between the load bearing capacity of CSPs and the ratio, which can be used to define “weak” or “strong” core and the status of postbuckling load bearing capacity (PLBC); (2) local failures of the core and face sheets (FSs) can lead to a drastic decrease in the local stiffness of CSPs, a singularity of the tangent stiffness matrix and the occurrence of secondary bucklings of CSPs; (3) secondary bifurcation identification, branch switching and convergence improvement are all necessary to obtain reasonable paths during the path-following.
       
  • Hypersonic flow characteristics and relevant structure thermal response
           induced by the novel combined spike-aerodome and lateral jet strategy
    • Abstract: Publication date: Available online 10 October 2019Source: Aerospace Science and TechnologyAuthor(s): Liang Zhu, Yingkun Li, Xiong Chen, Hao Li, Weixuan Li, Chunlei Li Huge aerodynamic drag and severe aeroheating are the inevitable challenges for hypersonic vehicles, this paper proposes a novel combined spike-aerodome and lateral jet strategy for drag reduction and thermal protection. Meanwhile, the hypersonic flow characteristics and structure thermal response are numerically investigated by an in-house code. The obtained results demonstrate that this novel strategy not only further reduces the total drag, but also provides excellent thermal protection for both the blunt body and spike rod. Then the effects of lateral jet pressure ratio, spike length and aerodome diameter on the flow properties, drag and heat reduction performance are thoroughly explored. Increasing the lateral jet pressure ratio can effectively enhance the thermal protection. Surprisingly, in a certain range, higher lateral jet pressure ratio even leads to larger pressure peak value on the blunt body. Increasing the spike length would enhance the heat transfer along the blunt body surface, and the total drag changes non-monotonically as the spike length varies. The total drag rises significantly when the aerodome diameter increases, and it can be increased by 40.1% when the aerodome diameter ratio increases from 0.15 to 0.5. Besides, increasing the aerodome diameter is beneficial to remarkably enhance thermal protection.
       
  • Aerodynamic performance investigation on a morphing unmanned aerial
           vehicle with bio-inspired discrete wing structures
    • Abstract: Publication date: Available online 10 October 2019Source: Aerospace Science and TechnologyAuthor(s): Zhe Hui, Yang Zhang, Gang Chen The excellent flight ability of birds is closely related not only to the morphing skeleton structure that can cause large-scale geometrical changes of their wings but also to the discrete or discontinuous wing structure composed of many feathers. In this study, a bio-inspired morphing discrete wing inspired from a pigeon's wing structure was designed with bionic feathers, with the explicit aim of improving the aerodynamic performance of an unmanned aerial vehicle. The bio-inspired discrete wing structure, controlled by a morphing skeleton structure, can actively morph into different swept-wing configurations similar to the wing postures of the pigeon and maintain a discrete wing surface similar to the pigeon wing surface at the same time. The results reveal that the bio-inspired morphing UAV can always maintain an optimal lift-to-drag ratio at three different Reynolds numbers utilizing the symmetrical wing morphing. The asymmetrical wing morphing can well achieve rolling control of the UAV. Furthermore, compared with a continuous wing surface structure, the bio-inspired discrete wing surface structure not only can achieve the induced drag reduction of the UAV through effectively decreasing the wing-tip vortex strength but also improve the lateral stability of the UAV.
       
  • Flutter analysis of sandwich plates with functionally graded face sheets
           in thermal environment
    • Abstract: Publication date: Available online 10 October 2019Source: Aerospace Science and TechnologyAuthor(s): Korosh Khorshidi, Mahdi Karimi This paper presents an analytical model for flutter analysis of sandwich plates with functionally graded face sheets in the thermal environment. The material properties of the face sheets are supposed to be temperature-dependent by a nonlinear distribution satisfying one-dimensional heat equation, and vary according to power law distribution in terms of the volume fractions along the thickness of the plate. The vibration of the sandwich plate is modeled on the basis of different plate theories including Mindlin theory, classical theory, exponential theory, third-order theory, sinusoidal theory, hyperbolic theory and fifth-order theory. Modified shear deformation theories applied herein are capable of considering inertia effects and transverse shear stresses. First order piston theory is utilized to model the aerodynamic load due to supersonic flow. The coupled governing equations are derived using Hamilton's principle and, Galerkin approach is applied to obtain vibrational characteristics and critical dynamic pressure of the system. Some comparisons with available results in the literature are performed to validate the present modeling, and excellent agreement is observed. Our attention is focused on analyzing the effects of different parameters such as thickness ratio, aspect ratio, thermal load, the thickness of face sheet and power law index on dynamic stability of the sandwich plate.
       
  • Robust formation flying control for a team of satellites subject to
           nonlinearities and uncertainties
    • Abstract: Publication date: Available online 8 October 2019Source: Aerospace Science and TechnologyAuthor(s): Hao Liu, Yu Tian, Frank L. Lewis, Yan Wan, Kimon P. Valavanis This paper addresses the problem of robust formation controller design for a group of satellites the dynamics of which involve nonlinearities and uncertainties. A formation flying controller is proposed for the satellite group, which includes a position controller to form the desired accurate formation and an attitude controller to align the satellite attitudes. It is shown that the trajectory and attitude tracking errors of the overall closed-loop control system can converge into a given neighborhood of the origin in a finite time. Numerical simulation studies are provided to demonstrate the advantages of the proposed formation control scheme.
       
  • Space-time accurate finite-state dynamic inflow modeling for aeromechanics
           of rotorcraft
    • Abstract: Publication date: Available online 8 October 2019Source: Aerospace Science and TechnologyAuthor(s): Felice Cardito, Riccardo Gori, Jacopo Serafini, Giovanni Bernardini, Massimo Gennaretti Wake inflow modeling is a crucial issue in the development of efficient and high-fidelity simulation tools for rotorcraft flight dynamics and aeroelasticity. This paper proposes a space-time accurate, finite-state, dynamic wake inflow modeling suitable for conventional and innovative rotor configurations, based on simulations provided by high-fidelity aerodynamic solvers. It relates the coefficients of a rotor-disc, radial-azimuthal wake inflow distribution to the rotor kinematic variables, and is capable to take into account the intrinsic periodicity of aerodynamic responses of rotors in steady forward flight. The proposed inflow modeling consists of a three-step process: (i) numerical evaluation of wake inflow due to perturbations of rotor kinematic variables, (ii) determination of transfer functions of multi-harmonic components of a suitable set of inflow coordinates, followed by (iii) their rational approximation and transformation into time domain to derive the differential operators governing multi-harmonic dynamics. The numerical investigation concerns the derivation of finite-state inflow models for single and coaxial rotors, through application of an aerodynamic boundary-element-method solver for potential flows. These are successfully validated by comparison with inflows directly calculated by the aerodynamic tool for arbitrary rotor perturbations.
       
  • Evaluation of vibration reduction devices for helicopter ride quality
           improvement
    • Abstract: Publication date: Available online 8 October 2019Source: Aerospace Science and TechnologyAuthor(s): Aykut Tamer, Vincenzo Muscarello, Pierangelo Masarati, Giuseppe Quaranta This work presents the use of a modern helicopter simulation environment for the evaluation of the combined performance of several systems for helicopter ride quality assessment. The proposed framework can handle increasingly detailed aeroservoelastic helicopter models while providing great flexibility and versatility in modeling human biodynamic models for vibration evaluation as well as models of the vibration attenuation devices. A numerical model representative of a medium weight helicopter is used to demonstrate the approach. Lumped parameter models of seat-cushion and human biodynamics are dynamically coupled to the helicopter model to provide a more realistic estimate of the actual vibratory level experienced by the occupants. Two performance indicators are formulated, based on the acceleration of the seat locations and using the ISO-2631 standard: i) qualitative criteria and related vibration dose values of the individuals seated at prescribed locations of a fully occupied helicopter, and ii) an overall rating of the occupants inside the cabin, considering the most and least comfortable seating distributions as the number of occupants changes. To demonstrate the proposed method, three configurations of helicopter-specific passive vibration absorbers are considered.
       
  • Robust attitude control for a rigid-flexible-rigid microsatellite with
           multiple uncertainties and input saturations
    • Abstract: Publication date: Available online 7 October 2019Source: Aerospace Science and TechnologyAuthor(s): Liming Fan, Hai Huang, Liang Sun, Kaixing Zhou In this paper, the attitude tracking system of a microsatellite consisting of a rigid main-satellite, a flexible coilable mast and a rigid sub-satellite is studied. The attitude tracking model is formulated as a highly nonlinear and coupled system subject to parametric perturbations, external disturbances, flexible vibration and input saturations. To realize the high-accuracy attitude tracking control, a robust controller consisting of a nominal controller, an observer-based compensator and a modified proportional-derivative (MPD) controller is proposed with a simple configuration. The nominal controller is introduced based on a disturbance-free nominal system. The observer-based compensator is constructed to compensate a lumped equivalent disturbance representing all uncertainties and disturbances in a finite time. The MPD controller is developed to implement the high-accuracy attitude control under input saturations. Stability analysis indicates that both attitude tracking errors and angular velocity tracking errors of the closed-loop system can converge asymptotically. To verify the effectiveness of the proposed control law, numerical simulations are launched in different cases. Simulation results demonstrate that the proposed control law not only achieves the high-accuracy attitude tracking control, but also suppresses the vibration of the flexible coilable mast.
       
  • Vibration analysis of circular and annular plates made of 3D graphene
           foams via Chebyshev-Ritz method
    • Abstract: Publication date: December 2019Source: Aerospace Science and Technology, Volume 95Author(s): Yan Qing Wang, Mei Wen Teng This paper focuses on the free vibration of circular and annular three-dimensional graphene foam (3D-GrF) plates under various boundary conditions. The Chebyshev-Ritz method is developed to solve the present problem. Different types of foam distribution are considered and the effective elastic modulus and mass density vary along the thickness or radial directions of the plates. The Kirchhoff plate theory is employed to derive the energy equations of the 3D-GrF plates. The numerical results show that the developed method has good accuracy and stability for analyzing free vibration problem of circular and annular 3D-GrF plates. It is also found that the increase in foam coefficient leads to the decrease in natural frequencies of 3D-GrF plates. Among different types of foam distribution, the 3D-GrF-I results in the highest natural frequency while the 3D-GrF-II corresponds to the lowest natural frequency of circular and annular 3D-GrF plates for most cases, depending on the specific boundary condition and foam coefficient. Moreover, the foam coefficient, the boundary condition, and the foam distribution interact with each other and have coupled effect on free vibration characteristics of 3D-GrF plates.
       
  • Experimental study of spray characteristics of liquid jets in supersonic
           crossflow
    • Abstract: Publication date: December 2019Source: Aerospace Science and Technology, Volume 95Author(s): Chenyang Li, Chun Li, Feng Xiao, Qinglian Li, Yuanhao Zhu The spray characteristics of a water jet in Mach 2.85 air crossflow were investigated experimentally using a Phase Doppler Anemometry system. The droplet diameter and velocity of liquid jets with various nozzle diameters were measured and analyzed. Experiments with liquid jets positioned ahead of a cavity were performed to investigate the effects of the cavity on the spray characteristics. It was found that the Sauter Mean Diameter distribution presented a C shape, and the streamwise velocity component presented a mirrored C shape. The Sauter Mean Diameter increased downstream in the upper layer of the liquid jet spray, and this is because large droplets are more prone than small droplets to move from the lower layer to the upper layer of the liquid jet, resulting in a larger Sauter Mean Diameter downstream. A smaller nozzle resulted in an earlier secondary atomization and the final Sauter Mean Diameter had a lower value. A comparison between liquid jets from a plane wall and those positioned ahead of a cavity found an increase in Sauter Mean Diameter near the shear layer of the cavity and a decrease in the streamwise velocity. This mixing process caused an oblique airflow at the outlet of the cavity and changed the distribution of droplets.
       
  • Reliability assessment for system-level turbine disc structure using
           LRPIM-based surrogate model considering multi-failure modes correlation
    • Abstract: Publication date: December 2019Source: Aerospace Science and Technology, Volume 95Author(s): Rongqiao Wang, Xi Liu, Dianyin Hu, Jianxing Mao This paper presents a probabilistic analysis framework for the reliability evaluation of turbine disc considering the correlation of multi-failure modes. A system-level zone division method is first applied to decompose the whole structure into different serial zones. Due to the same input random variables, there is correlation between failure modes. Thus, a mathematical copula function method is introduced to quantify the correlation between failure modes after reliability calculation of separate zones, during which process, dependent random variables are transformed to independent ones using Nataf transformation method. Meanwhile, to guarantee the accuracy and efficiency of calculation, adaptive surrogate model based on local radial point interpolation method (LRPIM) is established in each zone. Two main failure modes, i.e., low cycle fatigue and creep-fatigue are considered during the reliability analysis on a turbine disc. The results reveal that the reliability of the turbine disc changes with the correlation between failure modes. Also, sensitivity analysis shows that rotating speed and maximum temperature are two dominant factors affecting the turbined disc's reliability. Finally, the comparisons among three methods including the proposed method, the zone-based method without considering correlation and Monte Carlo (MC) method based on physics of failure (POF) of correlation are conducted. It is demonstrated that the proposed method in this study is more efficient and accurate for evaluating structural reliability with multi-failure modes coupling. Moreover, the proposed method provides an available prospect for reliability-based design optimization of multiple failure structure, contributing to enhance reliability in mechanical design.
       
  • Liquid hydrogen fuel tanks for commercial aviation: Structural sizing and
           stress analysis
    • Abstract: Publication date: December 2019Source: Aerospace Science and Technology, Volume 95Author(s): Arturo Gomez, Howard Smith LH2 fuel tanks are one of the main drivers in the development of a commercial airplane powered with hydrogen. This article discusses the implementation of liquid hydrogen fuel tanks in future commercial airplanes focusing on the sizing of the fuel tank structure and its behavior under critical loading conditions. Fuel tanks are sized according to the mission requirements and geometrical restrictions of a conventional mid-range commercial airplane. Critical loading cases for symmetrical maneuvers and landing conditions are estimated following EASA CS-25 airworthiness specifications for large airplanes. The stress distribution in each tank is evaluated using linear Finite Element Analysis (FEA) in MSC. NASTRAN/PATRAN to ensure that the structural design complies with strength and stiffness requirements
       
  • Integrated design of trajectory tracking and inertia property
           identification for post-capture of non-cooperative target
    • Abstract: Publication date: December 2019Source: Aerospace Science and Technology, Volume 95Author(s): Qin Zhao, Guangren Duan This paper investigates the post-capture control problem associated with trajectory tracking and inertia property identification for a six degree-of-freedom (6DOF) combined spacecraft system subject to input saturation. Post-capture of non-cooperative target will cause a large shift in the dynamics of combined spacecraft mainly resulting from the change of inertia properties. An adaptive tracking control law for combined spacecraft is designed based on the terminal sliding mode and dynamic surface control techniques, and the inertia properties can be identified simultaneously. To estimate mass and inertia matrix, the expression of parameter estimation error is obtained by introducing a group of auxiliary filtered variables. A saturation compensator is employed to deal with the input saturation. Within the Lyapunov framework, the proposed controller is proved to guarantee the finite-time convergence of both trajectory tracking and inertia property identification driven by continuous control forces. Numerical simulations are finally performed to demonstrate the effectiveness of the designed control law.
       
  • Envelope-constraint-based tracking control of air-breathing hypersonic
           vehicles
    • Abstract: Publication date: December 2019Source: Aerospace Science and Technology, Volume 95Author(s): Xiangwei Bu In this paper, a novel envelope-constraint-based neural controller is addressed for air-breathing hypersonic vehicles with unknown non-affine formulations. The vehicle dynamics is decomposed into velocity subsystem and altitude subsystem that are further described as unknown non-affine expressions. Neural networks are employed to approximate the unknown terms of each subsystem based on Mean Value Theorem, which rejects system uncertainties and non-affine characteristics. New learning algorithms are developed for adaptive parameters to stabilize the closed-loop system and reduce online parameters, yielding a low computational load design. The remarkable advantages are that complicated design procedure of back-stepping is avoided, and desired transient performance is guaranteed for velocity and altitude tracking errors via envelope constraint. The stability of closed-loop control system is proved utilizing Barrier Lyapunov functions. Finally, numerical simulation results are presented to validate the effectiveness of the proposed control approach.
       
  • Modeling and analysis of triggering pulse to thermoacoustic instability in
           an end-burning-grain model solid rocket motor
    • Abstract: Publication date: December 2019Source: Aerospace Science and Technology, Volume 95Author(s): Shixiang Ji, Bing Wang Occurrences of pulse-triggered instabilities in combustion chambers always trouble solid rocket motors (SRMs) in application. This paper performs numerical simulation of the pulse-triggered nonlinear instabilities in the end-burning-grain SRM, in use of the pressure-coupled response function to describe the spatiotemporal burning rate of AP-HTPB composite propellant grains. A high-order numerical solver realizes the cooperation of the burning rate model into the axisymmetric internal ballistic simulation of SRMs via the source terms in gas-phase governing equations. The analysis of high-amplitude pressure oscillations, which are the primary symptom of nonlinear thermoacoustic instabilities, provides the insight into the nature of the longitudinal instability growth process after the pulse triggering. The change rate of pressure fluctuation over the pressure fluctuation in the chamber is independent of the pulse intensity and triggering position. The growth characteristics of pressure oscillations for the present combustor system is neither affected by the pressure pulse intensity nor by the imposed regions in the flow field, while the higher pressure-coupled response function of the propellant promotes the growth process evidently. The present study is expected for the guidance of grain design in SRMs.
       
  • Experimental and numerical investigation of isolator in three-dimensional
           inward turning inlet
    • Abstract: Publication date: December 2019Source: Aerospace Science and Technology, Volume 95Author(s): Hu Ren, Huacheng Yuan, Jinsheng Zhang, Binqian Zhang Numerical simulation about a three-dimensional inward turning inlet with isolator and combustor was performed to study the flow field structure and flow characteristics of shock train. Cold and hot model wind tunnel experiments were carried out to compare the effects of cold and hot condition on shock train characteristics. The result shows that no oscillation phenomenon of the shock train was observed in the cold model experiment, but oscillation back and forth occurred in the hot model experiment. The trend of pressure distributions are consistent in cold and hot condition before the combustor. But it changed in the combustor where the pressure presented a continuous rising trend in cold condition, while a trend of rising first and then descending in hot condition. Establishing the corresponding relationship between throttling ratio and gas-oil ratio is beneficial to predict the property of the isolator in hot condition according to the cold condition.
       
  • Geometry and time updaters-based arbitrary-yaw iterative explicit guidance
           for fixed-thrust boost back of vertical take-off / vertical landing
           reusable launch vehicles
    • Abstract: Publication date: Available online 4 October 2019Source: Aerospace Science and TechnologyAuthor(s): Changzhu Wei, Xiaozhe Ju, Rong Wu, Yanfeng He, Yin Diao The typical return flight profile of vertical take-off / vertical landing (VTVL) reusable launch vehicles (RLVs) mainly comprises flip maneuver phase, boost back phase, grid fins deploy phase, among which the boost back phase plays a determinant role in accurate landing of reusable launch vehicles. In order to achieve pinpoint terminal precision in the boost back phase, a geometry and time updaters-based arbitrary-yaw iterative explicit guidance method is presented in this paper. By adopting an analytic motion predictor and abandoning small yaw angle hypothesis, the arbitrary-yaw iterative guidance law is formulated to deal with large yaw guidance problem caused by initial deviations and long-time flight. To compensate for the guidance errors due to the ignorance of terminal position constraint in the baseline guidance, a geometry updater is developed to update the target based on analytical geometry relationship. Furthermore, considering that the terminal target continuously moves following the earth, the time updater is designed to determine the candidate virtual orbit according to the estimated time-to-go. Simulations under various nominal flight trajectories and different initial deviations as well as the Monte Carlo simulation are carried out. Results illustrate that the proposed guidance algorithm performs well, showing high precision, strong adaptability and robustness.
       
  • Aero-mechanical multidisciplinary optimization of a high speed centrifugal
           impeller
    • Abstract: Publication date: Available online 3 October 2019Source: Aerospace Science and TechnologyAuthor(s): Chenxi Li, Jing Wang, Zhendong Guo, Liming Song, Jun Li An aero-mechanical multidisciplinary optimization was carried out for a high-speed centrifugal impeller, SRV2-O, by integrating a Self-adaptive Multi-Objective Differential Evolution (SMODE) algorithm, RANS solver technique, Finite Element Method (FEM), and data mining technique of analysis of variance (ANOVA) Specifically, the optimization of the impeller was conducted for the maximization of isentropic efficiency and the minimization of maximum stress. During optimization, constraints were imposed on the total pressure ratio at the optimization point and the mass flow rate at the choked point as well. Where, the former constraint intends to guarantee the working capability of the impeller while the latter tries to fix the working range. After optimization, six optimal Pareto solutions are finally obtained. The isentropic efficiency of the optimal solutions is increased by 2.07% at most while the maximum stress is decreased by 6.36% at most among the Pareto solutions. The better performance of optimal designs was demonstrated through detailed aerodynamic and mechanical analysis. Then, the ANOVA is used to explore the effects of variables on performance function in design, it is found that, the design variables located at the meridian channel and the leading edge of the full blade have significant effect on aerodynamic performance. These variables are crucial to reduce the loss caused by shock wave at impeller inlet and the leakage flow at blade tip. Meanwhile, the design variables located near the leading edge of full blade root section have great effect on strength performance, as they are effective to decrease the bend of blades and thus reduce the maximum stress. Thereby, the better aeromechanical performance can be achieved by dedicated adjustment on the curves of both the shroud of meridional channel and leading edge of full blade. The results of ANOVA are consistent with the aero-mechanical analysis. Therefore, the effectiveness of aero-mechanical optimization and data mining framework is demonstrated.
       
  • Switched linear parameter-varying modeling and tracking control for
           flexible hypersonic vehicle
    • Abstract: Publication date: Available online 1 October 2019Source: Aerospace Science and TechnologyAuthor(s): Lixian Zhang, Liang Nie, Bo Cai, Shuai Yuan, Dongzhe Wang In this paper, the reference tracking problem for a class of flexible hypersonic vehicles, whose dynamics vary significantly as flight states changes, is investigated via a novel switched linear parameter-varying (LPV) framework. Specifically, ranges of velocity and altitude are divided into several partitions, and the flexible hypersonic vehicle dynamics is modeled as a LPV system in each partition. Then the switched LPV model for the underlying system is obtained over a wide range of operating conditions. Switched LPV tracking controllers based on the developed model are established under mode independent/dependent persistent dwell time (PDT/MPDT) switching signals, respectively. Compared with the conventional mode independent/dependent average dwell time (ADT/MADT) switching signals, the proposed PDT/MPDT switching signals can address some more general flight variations, such as slow maneuvers and frequent rapid maneuvers coexist in the same flight mission. Furthermore, stringent transient and steady-state performance and a guaranteed non-weighted H∞ performance are achieved with the aid of multiple Lyapunov-like functions. A simulation is used to illustrate the designed controller via two proposed switching signals.
       
  • Maximum correntropy generalized high-degree cubature Kalman filter with
           application to the attitude determination system of missile
    • Abstract: Publication date: Available online 1 October 2019Source: Aerospace Science and TechnologyAuthor(s): Di Liu, Xiyuan Chen, Yuan Xu, Xiao Liu, Chunfeng Shi For SINS/CNS integrated navigation system, the CKF can perform well for state estimation in Gaussian noise. However, its performances are likely to degrade significantly under non-Gaussian noise conditions. To improve the robustness of the CKF against non-Gaussian noise, we propose an improved cubature Kalman filter, called the maximum correntropy generalized high-degree CKF (MCGHCKF). In the MCGHCKF, the generalized high-degree cubature rule is used to improve the filtering performance, and the maximum correntropy criterion is utilized to reduce the influence of non-Gaussian noise on state estimation. Simulation experiments illustrate the effectiveness and robustness of our algorithm.
       
  • On the dispersion of cylinder guided waves propagating in a multilayer
           composite hollow cylinder made of anisotropic materials
    • Abstract: Publication date: Available online 30 September 2019Source: Aerospace Science and TechnologyAuthor(s): Mingfang Zheng, Hongwei Ma, Yan Lyu, Cunfu He, Chao Lu The formula system of the state-vector and Legendre polynomials hybrid method (SV-LPHM) was applied to produce the dispersion curves and mode shape for the general anisotropic multilayer composite cylinders with whatever the dissimilarities of the layer material properties. According to relevant literature's reports, traditional Legendre polynomial method was only able to deal with the multilayer system where the material properties of adjacent layers are not significantly changed. To overcome the drawback, we introduce the state vector method to reshape the wave equation, boundary conditions and interface continuous conditions of the multilayer hollow cylinder in a consistent manner. Moreover, expanding the displacement field by the Legendre polynomials, and then a complete and concise state matrix form is formed for dispersion equation after complex algebraic transformation. All the matrices involving the mass and stiffness have been deduced analytically by the recurrence relation and orthogonality of the Legendre polynomial. The abovementioned operation overcomes the cumbersome when applying traditional Legendre polynomial method to dealing with the interface displacement and stress continuity. Firstly, we outlined the derivation of the formalism of the hybrid method (SV-LPHM) for guided waves propagating in the anisotropic multilayer hollow cylinder with an arbitrary number of layers. And then we demonstrated the SV-LPHM technique on the composite pipe of isotropic material and anisotropic material, where the key-factors of phase speed, displacement, and stress distribution were assessed and elaborated thoroughly. The results confirm the exponential convergence of the SV-LPHM compared with finite element methods.
       
  • Direct numerical simulation of fine flow structures of subsonic-supersonic
           mixing layer
    • Abstract: Publication date: Available online 30 September 2019Source: Aerospace Science and TechnologyAuthor(s): Liu Yang, Ma Dong, Fu Benshuai, Li Qiang, Zhang Chenxi Subsonic-supersonic mixing flow is one of the important research fields in turbulence research. For example, in the combustion chamber of the rocket ramjet combination engine, the rocket jet flow and the air inflow is a typical shear mixing flow, which has the characteristics of high convection Mach number and large flow parameter gradient. It is of great significance to explore the development law and flow structure of subsonic-supersonic mixing layer to enhance the mixing and thus improve the performance of rocket ramjet engine.In this paper, in order to further study the evolution process and obtain the evolution mechanism and fine flow structure of subsonic-supersonic mixing layer, three groups of high-order format direct numerical simulations of typical working conditions are carried out. The convective Mach numbers are 0.69, 0.92 and 1.27, respectively. The direct numerical simulation results show that: (1) the large-scale structure in the subsonic-supersonic shear mixing flow formed the small-scale structure earlier, and the flow was dominated by the small-scale and broken eddy structure; (2) the development process of the subsonic-supersonic shear mixing flow was mainly divided into three stages: laminar flow zone, transition zone and development zone. The transition zone was a transition zone from two-dimensional to three-dimensional, which began to show three-dimensional flow characteristics. The vorticity shows a twisted-winding structure. The large-scale Coherent structure, the Λ eddy and hairpin eddy, can be observed, and the Λ eddy structure is gradually elongated with the increase of convective Mach number; (3) the shocklets structure mainly occurs in the stage when the mixing layer has not fully developed. The starting point of the shocklets structure is near the vortex core. With the increase of convective Mach number, the position of the shocklets generation moves to the front of the vortex core; (4) the dynamic mode decomposition results show that the eigenvalues of each mode are basically located in the unit circle, which indicates that the calculated modes are stable; in addition, it is found that there is a certain dominant frequency in the flow structure, which can provide a reference for the active mixing enhancement method.
       
  • Radiative and evaporative characteristics analysis of a liquid droplet
           layer for space applications
    • Abstract: Publication date: Available online 30 September 2019Source: Aerospace Science and TechnologyAuthor(s): Hao Qin, Chenglong Wang, Dalin Zhang, Wenxi Tian, G.H. Su, Suizheng Qiu Liquid droplet radiator is promised to be used for waste heat dissipation of the large power space nuclear reactor. This paper analyzes the radiative heat transfer and evaporative characteristics by treating the droplet layer as a participating medium. The silicon oil is adopted as the working fluid. The mathematical models are established. The effects of the optical thickness κD, initial temperature, and flight time on the droplet radiation and evaporation are investigated. The main works are listed as follows: Firstly, the grid independence analysis of the temperature calculation is conducted, and the grid number on the thickness direction is suggested to be 100 times of κD. Secondly, the calculation results obtained from the one dimensional (1-D) simplified formula and the two dimensional (2-D) simulation have been compared, proving that it is acceptable to obtain the average temperature by 1-D simulation for droplet layers with any κD. Thirdly, detailed temperature distribution is calculated for both thin and thick droplet layers, and higher initial temperature and longer flight time can enhance the radiative heat transfer. Finally, the evaporative loss rate of the working fluid is found to be nearly constant with κD larger than 4. This paper may contribute to the thermal design and optimization of the liquid droplet radiator for space applications.
       
  • Design of high accuracy cylindrical profile measurement model for
           low-pressure turbine shaft of aero engine
    • Abstract: Publication date: Available online 30 September 2019Source: Aerospace Science and TechnologyAuthor(s): Chuanzhi Sun, Baosheng Wang, Yongmeng Liu, Xiaoming Wang, Chengtian Li, Hongye Wang, Jiubin Tan Coaxiality and cylindricity are the important geometric parameters of the low-pressure turbine (LPT) shaft. And the measurement accuracy of coaxiality and cylindricity directly affect the rotary characteristics of the aero engine. Therefore, a cylindrical profile measurement model with five systematic errors is designed to improve the coaxiality and cylindricity measurement accuracy of the low-pressure turbine shaft in this paper, in which eccentricity, probe offset, probe radius, geometric axis tilt and guide rail tilt are considered. Besides, the influence of systematic error and the shaft radius on the residual error for the stepped low-pressure turbine shaft is analyzed as well. The evaluation results of coaxiality and cylindricity are obtained based on different measurement strategies and models. In order to verify the effectiveness of the cylindrical profile measurement model with five systematic errors in the paper, a rotary measuring instrument with high precision is built. Compared with the traditional cylindrical profile measurement model with two systematic errors, the measurement accuracy of the coaxiality and cylindricity by the cylindrical profile measurement model with five systematic errors proposed in this paper are improved by 2.9 μm and 8.18 μm, respectively in the condition of the optimal measurement strategy for the LPT shaft with large radius. The proposed method is suitable for small probe radius and large eccentricity error, probe offset error, geometric axis tilt error and guide rail tilt error, especially for the LPT shaft with large radius. The proposed method can be applied to error separation and tolerance allocation for multistage rotor.
       
  • Spiral-diving trajectory optimization for hypersonic vehicles by
           second-order cone programming
    • Abstract: Publication date: Available online 26 September 2019Source: Aerospace Science and TechnologyAuthor(s): Lei He, Xiaodong Yan, Shuo Tang Spiral maneuvering targets are well known to be very difficult to intercept due to its high maneuverability and unpredictability. This paper focuses on the optimization of a spiral-diving trajectory for a hypersonic vehicle to strike a stationary target. Second-order cone programming (SOCP), a subclass of convex optimization, is applied to achieve this optimization task. First, based on a detailed analysis of spiraling nature, the dynamics are partially reconstructed to better formulate the spiraling motion. Then, a nonconvex optimal control problem is formulated with the maximum impact velocity as a performance index. Constraints on the states, controls, and terminal conditions are helping to shape a feasible and practical spiraling trajectory. This nonconvex problem is convexified and subsequently discretized in a suitable form so that it can be easily solved in polynomial time using the existing primal-dual interior-point algorithm. In addition, a relaxation technique is used to convexify control constraints and is theoretically proved to be valid. The high reliability and efficiency of the successive SOCP method are verified by numerical examples and comparisons with other methods.
       
  • Observer-based H ∞ fault-tolerant attitude control for satellite with
           actuator and sensor faults
    • Abstract: Publication date: Available online 26 September 2019Source: Aerospace Science and TechnologyAuthor(s): Xiaohui Liang, Qing Wang, Changhua Hu, Chaoyang Dong This paper investigates the fault-tolerant attitude stabilization control problem for the satellite system subject to actuator failures, sensor failures and external disturbances. First, the H∞ observer is designed to estimate both system states and faults simultaneously. In order to reduce the effect of faults or failures, an auxiliary observer is introduced to improve the observation precision. Exploiting a novel auxiliary variable, the unavailable term in auxiliary observer is eliminated and the real observer is achieved. Second, the observer-based output feedback fault-tolerant control scheme is proposed for the satellite systems to handle actuator and sensor faults, which can stabilize the attitude angle and angular velocity with high precision. Finally, the effectiveness of proposed method is demonstrated via the simulation experiments.
       
  • Evaluation method of riblets effects and application on a missile surface
    • Abstract: Publication date: Available online 25 September 2019Source: Aerospace Science and TechnologyAuthor(s): Jiahe Li, Yanming Liu, Jiang Wang To overcome the difficulties of numerical simulation for riblets drag reduction effects on large-scale aircraft model, a riblet-equivalent boundary condition is introduced by modifying wall ω value, which makes the riblets effects can be calculated with a conventional smooth wall by RANS computation. Firstly, an empirical formula is deduced by analyzing various experiment results, and the function relationship between nondimensional geometry factor h+ and wall ω value is established. Secondly, the verifications for riblet-equivalent boundary condition are conducted on both zero and adverse pressure flow, by comparing the numerical simulation results with experimental data, which indicates a good reliability of this new method. Finally, an application of riblet-equivalent boundary condition is conducted on a typical configuration missile. Three riblets surface cases are introduced, with various riblets geometry factors. Flow parameters are analyzed for presenting the flow structure and performance of riblets surface. The positive conclusions are obtained that a 2.4% total drag reduction and a 4.6% skin friction reduction are gained.
       
  • A conditional cubature Kalman filter and its application to transfer
           alignment of distributed position and orientation system
    • Abstract: Publication date: Available online 23 September 2019Source: Aerospace Science and TechnologyAuthor(s): Xiaolin Gong, Longjun Chen Aiming at the problems of the accuracy and real-time performance in transfer alignment of airborne distributed position and orientation system (POS), a conditional cubature Kalman filter (CCKF) is proposed. In this method, the state variables of the non-linear mathematical model for transfer alignment are divided into two groups firstly—one group are linear variables that are independent with nonlinear variables, while the other group is composed of nonlinear variables and the linear ones coupled with them. And then, sampling is conducted to the second group of variables to realize the propagation of the cubature points, and the first group of variables is updated by using the conditional distribution of high-dimensional Gaussian random variables at the same time, therefore, time update for all state variables is completed. In the end, measurement update is performed for all state variables. The simulations results show that the proposed method can effectively reduce the computation burden while ensure the accuracy of transfer alignment.
       
  • Coupling method of stability enhancement based on casing treatments in an
           axial compressor
    • Abstract: Publication date: Available online 2 October 2019Source: Aerospace Science and TechnologyAuthor(s): Wei Wang, Jin-ling Lu, Xing-qi Luo, Wu-li Chu Casing treatment utilized in aircraft compressors is characterized by its powerful capacity of enhancing stability but causes remarkable efficiency penalty. To deal with this problem, we tested several types of casing treatments, including slots, grooves, recirculating casing treatments, and a composite structure to understand their characteristics. The test results show that different casing treatments can be combined to obtain a higher compressor stability, and the efficiency penalty can be decreased by implementing a novel flow management technology. Based on the results, a coupled casing treatment (CCT) that is constructed with slots, injectors, and a plenum chamber is proposed and optimized in the present study. The optimized CCT improves compressor stability by 16.7% with no penalty on the compressor efficiency. Two flow circulations, namely, an inner circulation in the slots and an outer circulation from the slots to the injectors, which dampen the development of tip leakage vortex, account for the excellent stability enhancement. The outer circulation, defined as the coupling effect, has generally a positive effect on compressor stability and a negative effect on the compressor efficiency. The effects of the length and numbers of the slots on the coupling effect are more significant compared to the slot location. The hysteresis effect that the recovery of tip blockage lags behind that of the tip leakage vortex cannot be established due to inadequate injection energy actuated in the CCT. As a result, a circumferentially discrete distribution of recirculating loops cannot improve compressor stability satisfactorily. As the CCT convers the full annulus, a much higher stability is obtained, and the boundary layer at the rear part of blade passages is severely separated when approaching the stall limit, which ultimately triggers compressor stall rather than the tip leakage vortex. The stall inception behaves as a full-annulus-dimension collapse with the flow phenomena of backflow at the trailing edge and forward spillage at the leading edge of the blade.
       
  • An elliptical region method for identifying a vortex with indications of
           its compressibility and swirling pattern
    • Abstract: Publication date: Available online 2 October 2019Source: Aerospace Science and TechnologyAuthor(s): Yangwei Liu, Yumeng Tang A local trace criterion (LTcri) is proposed to identify the vortex, and a projection plane with an analytical elliptical region (ER) corresponding to the LTcri is constructed to indicate the compressibility and swirling pattern of the recognised vortex region simultaneously. The analytical expression of the three components of the complex eigenvalues are provided to formulate the positive-Delta space as the projection plane. Flow points that projected inside the elliptical region could be thought as constructing the vortex with the projected location indicating the compressibility and the swirling patterns of the local fluid. With the analytical resolution given, the LTcri based ER (LTER) indication method is easy to implement in a pointwise manner, and it is suitable for the local analysis of a time-frozen flow field, both compressible and incompressible. The method is also Galilean invariant and it overcomes the imperfection of threshold choice in region-type methods. A compressor corner separation flow case with practical Mach number is analysed by the LTER indication method. The potential of the proposed method is shown both in distinguishing the different swirling patterns of complex vortices in tangle as well as analysing their evolution mechanism, through the regional indication.
       
  • Dynamic surrogate modeling approach for probabilistic creep-fatigue life
           evaluation of turbine disks
    • Abstract: Publication date: Available online 2 October 2019Source: Aerospace Science and TechnologyAuthor(s): Lu-Kai Song, Guang-Chen Bai, Cheng-Wei Fei To improve the modeling accuracy and simulation efficiency of probabilistic creep-fatigue life evaluation, a decomposed collaborative time-variant Kriging surrogate model (DCTKS) is proposed by absorbing the strengths of extremum selection technique and Kriging model into decomposed collaborative strategy. The probabilistic creep-fatigue life evaluation of a typical turbine disk is considered as one case to evaluate the proposed DCTKS method with respect to fluctuation of transient loads, nonlinearity of material properties and variability of models. In respect of this study, we find that the probabilistic creep-fatigue life of the turbine disk under the reliability degree of 0.998 7 is 946 cycles, and the transient fluctuating loads (body temperature and rotor speed) are the main factors of influencing creep-fatigue life. Through the comparison of methods (DCTKS, Monte Carlo simulation method, Kriging surrogate method, decomposed collaborative response surface method), the proposed DCTKS is demonstrated to possess the computational advantages in efficiency and accuracy for probabilistic creep-fatigue life evaluation.
       
  • Investigations on oblique detonations induced by a finite wedge in high
           altitude
    • Abstract: Publication date: Available online 2 October 2019Source: Aerospace Science and TechnologyAuthor(s): Gaoxiang Xiang, Xudong Li, Xiaofeng Sun, Xiaopeng Chen In this paper, the characteristics of two-dimensional (2D) oblique detonation waves (ODWs) induced by finite wedges in high altitude are investigated numerically. The reactive Euler equations with a detailed chemical model are solved. This paper focuses on the effects of expansion waves and altitudes on ODW, including the initiation, wave structures, pressure and temperature distributions. Numerical results demonstrate that both the location of turning point from oblique wedge to horizontal wedge and the altitude influence the initiation characteristics of ODW. Then, the initiation criterion of ODW for finite wedges is proposed in this paper. As the characteristic length of induction zone LC (the length from the front point of oblique wedge to the front point of deflagration wave) and the characteristic length of oblique wedge LW satisfy the relationship LC/LW>1, the initiation of ODW occurs. When LC/LW
       
  • Flow simulation around 3D bodies by using Lagrangian vortex loops method
           with boundary condition satisfaction with respect to tangential velocity
           components
    • Abstract: Publication date: November 2019Source: Aerospace Science and Technology, Volume 94Author(s): S.A. Dergachev, I.K. Marchevsky, G.A. Shcheglov A new approach is developed for incompressible 3D flow simulation around bodies by Lagrangian vortex method. Closed vortex loops are considered as vortex elements, which are generated on all the body surface and provide the satisfaction of the boundary condition on the body surface. The procedure of the double layer potential density reconstruction, called T-scheme is proposed, which consists of two steps. Firstly, the integral equation with respect to vortex sheet intensity is solved, which expresses the equality between the tangential components of flow velocity limit value and the body surface velocity. It is solved by using Galerkin approach. Secondly, the least-squares procedure is implemented, which permits to find nodal values of the double layer potential density. It is shown that the developed algorithm makes it possible to improve significantly the quality of solution for the complex-shaped bodies with low-quality surface meshes. The combination of this approach with vortex wake modeling with vortex loops permits to simulate unsteady flows with acceptable computational complexity. It can be useful for CFD applications and visual effects reproducing in computer graphics.
       
  • Characterization of a novel open-ended shock tube facility based on
           detonation transmission tubing
    • Abstract: Publication date: November 2019Source: Aerospace Science and Technology, Volume 94Author(s): Guoshuai Li, Takahiro Ukai, Konstantinos Kontis This paper proposes and demonstrates a novel shock tube driven by commercially available detonation transmission tubing in a safe, repeatable, and controllable manner for laboratory scale experiments. A circular cross-sectional open-ended shock tube (inner-diameter D=22mm) driven by detonation transmission tubing was used to investigate the working principle of this novel shock tube using a dynamic pressure transducer and time-resolved shadowgraph photography. Specifically, the shock Mach number, repeatability, and flow structure generated from the tube exit were characterized. The experimental result shows that the flow structure including an initial shock wave, a vortex ring, an embedded shock, and an oblique shock pattern is similar to that of the conventional compressed-gas driven shock tubes. Furthermore, the shock tube has good repeatability of less than 2% with a shock Mach number up to 1.58. The versatile and cost-effective nature of the shock tube driven by detonation transmission tubing opens a new horizon for shock wave-assisted interdisciplinary applications.
       
  • Electric sail trajectory correction in presence of environmental
           uncertainties
    • Abstract: Publication date: November 2019Source: Aerospace Science and Technology, Volume 94Author(s): Andrea Caruso, Lorenzo Niccolai, Giovanni Mengali, Alessandro A. Quarta An Electric Solar Wind Sail (E-sail) is an innovative propellantless propulsion system that generates a propulsive acceleration by exchanging momentum with the solar wind charged particles. Optimal E-sail trajectories are usually investigated by assuming an average value of the solar wind characteristics, thus obtaining a deterministic reference trajectory. However, recent analyses have shown that the solar wind dynamic pressure should be modeled as a random variable and an E-sail-based spacecraft may hardly be steered toward a target celestial body in an uncertain environment with just an open-loop control law. Therefore, this paper proposes to solve such a problem with a combined control strategy that suitably adjusts the grid electric voltage in response to the measured value of the dynamic pressure, and counteracts the effects of the solar wind uncertainties by rectifying the nominal trajectory at suitably chosen points. The effectiveness of such an approach is verified by simulation using two-dimensional transfer scenarios.
       
  • Dynamics and control of de-spinning giant asteroids by small tethered
           spacecraft
    • Abstract: Publication date: November 2019Source: Aerospace Science and Technology, Volume 94Author(s): Junjie Kang, Zheng H. Zhu This paper investigates the de-spin control problem of giant asteroids by deploying small tethered spacecraft in the post-capture operation of asteroid redirection or space debris removal. Two simple and novel feedback control laws are developed based on dynamic characteristics of the tethered asteroid-spacecraft system. The first de-spins the asteroid by deploying tether at the tethered spacecraft to dissipate the kinetic energy of asteroid without consuming propellent. Although effective, this control law cannot de-spin the asteroid completely to the static state because of the stability deteriorates. To overcome the limitation, the second control law is developed by de-spinning the asteroid to the static state by deploying tether and firing a thrust at the tethered spacecraft simultaneously. The stability of both control laws is proved. Numerical simulation shows both control laws are effective.
       
  • The effect of hybridization on high-velocity impact response of carbon
           fiber-reinforced polymer composites using finite element modeling, Taguchi
           method and artificial neural network
    • Abstract: Publication date: November 2019Source: Aerospace Science and Technology, Volume 94Author(s): Mohammad Vahab Mousavi, Hadi Khoramishad In this paper, the effect of hybridization of carbon fiber-reinforced polymer (CFRP) composite laminates was investigated on the high-velocity impact responses of laminates using a validated finite element model, the Taguchi and the artificial neural network methods. The CFRP laminates were hybridized by replacing half of the carbon layers with glass and Kevlar laminae. It was found out that employing the right hybrid materials on the right position of the laminate can considerably change the damage pattern and consequently reduce the projectile residual velocity by increasing the energy absorbed by the CFRP laminate. Introducing four Kevlar laminae on the back of the CFRP composite laminate instead of the four carbon layers resulted the highest improvement in the laminate energy absorption by 67%. The hybrid laminates experienced wider damage zone and more extensive delamination compared to the CFRP laminate. Introducing the hybrid materials with high strength and strain to failure material such as Kevlar on the back of the laminate in the presence of CFRP front face can be considered as an appropriate hybrid composite laminate when exposed to high-velocity impact loading.
       
  • A novel methodology of sequential optimization and non-probabilistic
           time-dependent reliability analysis for multidisciplinary systems
    • Abstract: Publication date: November 2019Source: Aerospace Science and Technology, Volume 94Author(s): Lei Wang, Chuang Xiong Various uncertainties, which are usually time-dependent, affect the reliability of complicated engineering systems seriously. Considering the fact that only limited sample data of the uncertain variables can be obtained in engineering practice during the whole in-service time of multidisciplinary systems, the interval process model is introduced to model the time-dependent uncertain variables, and a non-probabilistic time-dependent reliability estimation model is proposed. In addition, a sequential multidisciplinary optimization and non-probabilistic time-dependent reliability assessment (SMO_NTRA) approach is developed to decouple the time-dependent reliability analysis from the multidisciplinary design optimization (MDO). In the framework of SMO_NTRA, the deterministic MDO and non-probabilistic time-dependent reliability analysis are executed in a sequential manner. Thus the computationally expensive double level optimization problem can be avoided and the efficiency can be greatly improved. Furthermore, the shifting distance of the constraint is calculated by bi-section method. Both numerical and engineering examples are employed to demonstrate the validity of the proposed method.
       
  • Impacts of jet angle and jet-to-crossflow pressure ratio on the mixing
           augmentation mechanism in a shcramjet engine
    • Abstract: Publication date: November 2019Source: Aerospace Science and Technology, Volume 94Author(s): Zhao-bo Du, Wei Huang, Li Yan, Min-zhou Dong The mixing process between the fuel and the incoming flow should be taken into consideration for the shock-induced combustion ramjet (shcramjet) engine, and this is pivotal for its successful engineering implementation. In the current study, the impacts of the gaseous fuel jet angle and the jet-to-crossflow pressure ratio are investigated numerically in order to make a foundational study and reveal the mixing augmentation mechanisms of different conditions. Flow fields windward and leeward are studied, and some parameters are provided to evaluate the flow field properties quantitatively, namely the mixing efficiency, the total pressure recovery coefficient, the fuel penetration depth and the mixing length. The obtained results predicted by the three-dimensional Reynolds-Averaged Navier-Stoke (RANS) equations coupled with the two equation shear stress transport (SST) k-ω turbulence model show that both the jet angle and the jet-to-crossflow pressure ratio have a great influence on the flow field, and the hydrogen distribution and streamwise vorticity downstream of the injectant orifice are affected seriously. The small jet angle and low jet-to-crossflow pressure ratio are more beneficial for the air-fuel mixing but with some shortcomings, and there needs an optimum result in the future to capture better achievement.
       
  • Effects of rotational motion on dynamic aeroelasticity of flexible
           spinning missile with large slenderness ratio
    • Abstract: Publication date: November 2019Source: Aerospace Science and Technology, Volume 94Author(s): Heng Li, ZhengYin Ye The structural rigidity of a spinning missile with large slenderness ratio is usually small, and the structural deformation and rate should not be ignored. Furthermore, rotational motion makes the aeroelasticity more complicated. Therefore, unsteady Euler equations and generalized dynamic aeroelastic equations are coupled simultaneously to simulate the dynamic aeroelastic response of a spinning missile with large slenderness ratio using rigid-motion mesh and radial-basis-function (RBF) morphing mesh techniques. The unsteady Euler equations are solved by computational fluid dynamics (CFD) technique by the in-house code. The Coriolis term and centrifugal loading term due to rotational motion are both considered in the generalized dynamic aeroelastic equations. The rigid-motion mesh and RBF morphing mesh techniques are both based on unstructured mesh, and the rigid-motion mesh is adopted to treat the rigid motion due to rotational motion, while the RBF morphing mesh is employed for flexible structural deformation caused by aeroelasticity. Numerical results of aeroelastic case are well agreed with the experimental results, which validates the numerical method. A missile model with X-X configuration is constructed to investigate the effects of rotational motion on dynamic aeroelasticity. The dynamic aeroelastic responses of the missile with and without rotational motion are simulated, respectively. Comparison results show that the lateral modes and longitudinal modes are coupled together because of rotational motion. In addition, the structural natural frequencies are changed due to rotational motion. In the end, detailed numerical analysis of the generalized dynamic aeroelastic equations used in this paper indicates the mechanism by which the rotational motion leads to the coupling of lateral modes and longitudinal modes and changes the structural natural frequencies.
       
  • Effect of film cooling injection on aerodynamic performances of scramjet
           isolator
    • Abstract: Publication date: Available online 6 September 2019Source: Aerospace Science and TechnologyAuthor(s): Kuan Zheng, Wei Tian, Jiang Qin, Silong Zhang, Hui Hu With continuous increase in flight Mach number, aerodynamic heating on scramjet isolators becomes increasingly pronounced. Consequently, a thermal protection technique for scramjet isolators is urgently required. In the present study, a numerical investigation was conducted to evaluate the feasibility of applying film cooling on a scramjet isolator. First, the heat transfer characteristics under different coolant flow conditions (i.e., coolant Mach number, coolant total temperature, and injection position) were obtained to evaluate the film cooling efficiency on a scramjet isolator. Next, the characteristics of maximum backpressure and friction drag were analyzed to obtain the effects of film cooling injection on the aerodynamic performances of the scramjet isolator. It was found that the film cooling injection under proper coolant flow conditions could reduce the friction drag and enhance the ability of the isolator to resist backpressure, which is beneficial to the performances of a scramjet engine. In general, the results obtained in this study indicated that film cooling injection could be a practical thermal protection technique for a scramjet isolator.
       
  • Thermal flutter prediction at trajectory points of a hypersonic vehicle
           based on aerothermal synchronization algorithm
    • Abstract: Publication date: Available online 5 September 2019Source: Aerospace Science and TechnologyAuthor(s): Tongqing Guo, Ennan Shen, Zhiliang Lu, Di Zhou, Jiangpeng Wu Due to orders of magnitude differences in time scale between structural heat transfer and aeroelastic responses, one-way aerothermal-aeroelastic coupling is adopted to develop a thermal flutter prediction method for a hypersonic vehicle operating along a desired trajectory. In view of the strong dependency of the heat transfer process on the unsteady hypersonic trajectory, an aerothermal synchronization algorithm is established in a non-inertial frame of reference by formulating the governing equations of fluid flow and heat transfer into a unified form. Then the heated free-vibration frequencies and mode shapes are calculated at each trajectory point by using a finite-element analysis. Consequently, the flutter computations are performed on the transiently heated structure at each trajectory point by utilizing a coupled computational fluid dynamics (CFD)/computational structural dynamics (CSD) method. Because of the mass dissimilarity caused by directly increasing the dynamic pressure of a compressible flow, the technique of variable stiffness is introduced to evaluate the flutter dynamic pressure at the point of mass similarity and the stiffness margin of flutter. The present method is applied to the thermal flutter computations of a hypersonic all-movable rudder operating along a given trajectory. The computed temperature differences between the synchronization and conventional partitioned methods, and the significant effects of aerodynamic heating on the structural modes and the flutter characteristics are analyzed in detail.
       
  • Station-keeping strategy for real translunar libration point orbits using
           continuous thrust
    • Abstract: Publication date: Available online 5 September 2019Source: Aerospace Science and TechnologyAuthor(s): Yi Qi, Anton de Ruiter In this paper, we investigate the station-keeping strategy for translunar libration point orbits (LPOs) using the continuous thrust in the ephemeris model. Ephemeris models with and without the solar radiation pressure (SRP) are proposed for the numerical simulation. Three kinds of translunar LPOs, including halo orbits, vertical Lyapunov orbits, and Lissajous orbits, are used as nominal orbits. A station-keeping strategy based on the backstepping technique is extended to the ephemeris model. Then station keeping under practical constraints, caused by the navigation system and the executive system, is studied in ephemeris models with and without the SRP. Using numerical simulations, influences of the dead-band scheme, navigation errors, the navigation interval time and the area-to-mass ratio on station keeping are discussed, respectively. Furthermore, numerical simulations indicate that if the SRP is taken into account, LPOs obtained in the ephemeris model with the SRP is more preferable as nominal orbits than those without the SRP. More Monte-Carlo simulations testify that our control strategy can be applied to the long-term station keeping for different translunar LPOs.
       
  • Using approximate similitude to design dynamic similar models
    • Abstract: Publication date: Available online 4 September 2019Source: Aerospace Science and TechnologyAuthor(s): Afshin Banazadeh, Pedram Hajipouzadeh This research deals with the analysis of approximate similitude between the dynamic similar models and the full-scale prototype of an aircraft. Due to physical and technical constraints, a full dynamic similarity is not practically possible and previous works have all neglected one or two similarity criteria like Mach or Reynolds numbers for the sake of Froude number similarity. In this work, it is shown that Mach number has an important effect on aerodynamic characteristics and dynamic response of an aircraft and that neglecting it makes the generalization of the scale-model test data invalid for the full-scale prototype. In order to address this problem, a measurable quantity named approximate similitude parameter is proposed, which takes into account both dynamic similarity criteria and the scale model test objectives. The effectiveness of this parameter is shown by a case study to find out optimal weight, moments of inertia and velocity for the scale model to achieve optimal dynamic similarity.
       
  • Optimization design method for the cable network of mesh reflector
           antennas considering space thermal effects
    • Abstract: Publication date: Available online 4 September 2019Source: Aerospace Science and TechnologyAuthor(s): Rui Nie, Baiyan He, Shaoze Yan, Xiaofei Ma The mesh reflector antenna is widely used in space satellites for its characteristics of lightweight, large aperture, high precision, and high stiffness. As the form of mesh surface is heavily depended on cable forces and vice versa, the form finding and optimization design of cable networks play an essential role in antenna design. The present methods usually neglect the thermal effects, which is reasonable for ambient temperature. While space thermal loads cause significant variations from the original form finding state, it is essential to investigate and minimize the antenna's on-orbit shape errors caused by the thermal effects. The active shape adjustment on-orbit is far from anticipated, while the preliminary adjustment before launch is also limited by the number of adjustable cables (tension ties) and the engineer's experiences. Under these circumstances, we propose a form finding and design optimization approach for the cable network of mesh reflector antennas considering space thermal effects. In this approach, the cable's thermal deformation and geometric nonlinearity are fully considered at the design stage, and the burden of shape adjustment for thermal errors before launch can be relieved. As all cables instead of adjustable cables are optimized, the improvement of surface accuracy is more obvious than the shape adjustment method. Our work provides a new idea and approach for the optimization design of cable networks and the minimization of on-orbit shape errors.
       
  • H -based model following method in autolanding
           systems
    • Abstract: Publication date: Available online 4 September 2019Source: Aerospace Science and TechnologyAuthor(s): K. Tamkaya, L. Ucun, I. Ustoglu Probably the most important part during a flight is the landing phase because most of the accidents occur in this phase. Automatic landing systems (ALS) take over the control during this phase to avoid potential pilot-induced risks. However, some external disturbances such as windshear can jeopardize the safe landing. In this paper, the flare part of ALS is handled in a different way. A combination of some useful design methods is brought together to improve the performance of the conventional ALS even under severe weather conditions. Model following method is combined with the H∞ synthesis method to find out the optimal solution for a given cost function. Resultant H∞ optimal control problem is solved using Linear Matrix Inequalities (LMIs) and then a dynamic controller is constructed. On the other hand, the overall system is formed into P-K configuration, thus the system can be reconfigured easily when there exists a change in the system such as addition or removal of disturbance, noise and so on. We achieved significant performance on the system without any disturbance. In addition to that, the robustness takes an important role for the flight systems and needs to be handled correctly. Therefore, two kinds of windshear are taken care of and their effects minimized in a way that the tracking performance remains unaffected. Thus, highly considerable results are obtained using the proposed method even under severe weather conditions.
       
  • An experimental study on a coaxial flow with inner swirl: Vortex evolution
           and flow field mixing attributes
    • Abstract: Publication date: Available online 4 September 2019Source: Aerospace Science and TechnologyAuthor(s): A. Giannadakis, A. Naxakis, A. Romeos, K. Perrakis, Th. Panidis A 2D particle image velocimetry study of a coaxial flow with inner swirl is presented. An inner swirling jet, produced by tangential injection, interacts with an annular flow generating a recirculating flow field with strong mixing attributes. The characteristics of the cross-plane velocity components of four different test cases are presented (two levels of tangential injection flow rate combined with two levels of annular flow rate) in order to study the mean and turbulent attributes of the swirling vortex. The main features of this complex flow field, which can be considered as the interaction of a typical swirling jet undergoing “vortex breakdown” with an outer annular flow with “backward facing step flow” characteristics, are investigated, focusing on the swirling jet's characteristics. The analysis of the mean and turbulent flow is based on a modified Rossby number, previously proposed by the authors, defined as the ratio of the streamwise velocity jump across the two streams over a typical tangential velocity, which is shown to represent the ratio of the pressure difference due to the streamwise velocity difference and the entrainment of the two flows to that due to the rotation of the swirling vortex. The angular momentum diffusion downstream is evaluated, to assess the mixing between the swirling vortex and the outer flow.
       
  • Onboard satellite visibility prediction using metamodeling based framework
    • Abstract: Publication date: Available online 4 September 2019Source: Aerospace Science and TechnologyAuthor(s): Xinwei Wang, Chao Han, Pengbin Yang, Xiucong Sun Satellite autonomous systems are employed to address complex space applications through onboard data processing and mission planning. To take advantage of onboard autonomous systems, rapid onboard satellite visibility predictions are necessary for certain decision-making missions, including Earth observation resource allocation and satellite data transmission. We consider this visibility prediction process as a roots-finding problem for a multiple hump function, and design a metamodeling-based framework with a self-adaptive interpolation method. Metamodels are developed as surrogates for visibility prediction functions to reduce expensive computational costs. Our proposed framework has a broad range of applications for all orbital types and orbit propagators. We conduct the experiments using different metamodeling techniques, radial basis functions, Kriging, and support vector regression based upon real China's satellites. Numerical simulations indicate that the proposed framework outperforms existing interpolation methods, efficiently reducing the onboard computational cost.
       
  • Experimental investigation of gravity and channel size effects on flow
           boiling heat transfer under hypergravity
    • Abstract: Publication date: Available online 3 September 2019Source: Aerospace Science and TechnologyAuthor(s): Xiande Fang, Da Tang, Ling Zheng, Guohua Li, Yuliang Yuan Understanding of flow boiling heat transfer under hypergravity is needed due to its applications to modern flight vehicles. Few investigations on this issue have been reported. The present paper presents the experimental results of R134a flow boiling heat transfer in 1.002 and 2.168 mm ID tubes under hypergravity up to 3.16 g. The results reveal effects of gravity, channel size, heat flux, mass flux, quality, and pressure on and their interrelations in flow boiling heat transfer. Gravity has strong effects on flow boiling heat transfer. The heat transfer coefficients (HTCs) under hypergravity levels up to 3.16 g are normally greater than those under Earth's gravity. The heat transfer characteristics in the 1.002 and 2.168 mm tubes are very different, indicating that gravity effects on flow boiling heat transfer strongly interrelate with channel size. Also, gravity effects on flow boiling heat transfer are influenced by heat flux, mass flux, and pressure, and somewhat related to quality.
       
  • Control of Aeolian tones from a circular cylinder using forced oscillation
    • Abstract: Publication date: Available online 30 August 2019Source: Aerospace Science and TechnologyAuthor(s): Ruixian Maa, Zhansheng Liu, Guanghui Zhang, Con J. Doolan, Danielle J. Moreau Effects of forced transverse oscillation on the generation of sound from a circular cylinder immersed in uniform flow at a Reynolds number 150 and a Mach number 0.2 is investigated by direct numerical simulation. The cylinder is prescribed to oscillate sinusoidally with a constant oscillating amplitude ratio α of 0.2 of the cylinder diameter and oscillation frequency ratios F=0.2 to 1.4 of the inherent vortex shedding frequency. The impact of the oscillating frequency on the sound pressure is in accordance with that of the forces acted on the cylinder, by which three regimes are identified. In the first regime (F≤0.7), the sound levels are slightly affected by the oscillation. In the second regime, at 0.8≤F
       
  • A three variable refined shear deformation theory for porous functionally
           graded doubly curved shell analysis
    • Abstract: Publication date: Available online 26 August 2019Source: Aerospace Science and TechnologyAuthor(s): Minh-Chien Trinh, Seung-Eock Kim This study develops a three variable refined shear deformation theory to analyze the free vibration and bending behavior of porous functionally graded doubly curved shallow shells subjected to uniform and sinusoidal pressure. Shell displacements are assumed to be caused by extensional, bending, and shear effects. The in-plane displacements produced by bending effects are considered taking the form of the classical plate theory. The in-plane displacements produced by shear effects satisfy the stress-free and strain-free condition at the top and bottom surfaces, eliminating the usage of the shear correction factor in the present study. Two porosity types influence material properties and structure behaviors in different aspects. Hamilton's principle is used to derive Euler–Lagrange equations. Spatial solutions for the differential equation are assumed satisfying boundary conditions and their time-dependent amplitude equations are obtained by applying the Bubnov–Galerkin technique. Natural frequencies and transverse deflections of the shell in different geometry configurations and different porosity types and degrees are obtained and compared. The proposed theory is proved feasible to be applied in the analysis of functionally graded plates and shells with porosity.
       
  • Effects of bevelled nozzles on standoff shocks in supersonic impinging
           jets
    • Abstract: Publication date: Available online 2 September 2019Source: Aerospace Science and TechnologyAuthor(s): H.D. Lim, T.H. New, R. Mariani, Y.D. Cui Moderately under-expanded jets issuing from a circular baseline and two bevelled circular nozzles impinging upon a perpendicular flat plate were experimentally studied. The effects of nozzle-pressure-ratio and separation distance variations on the standoff shock formations were investigated with schlieren visualizations and a visual hull based three-dimensional (3D) shock reconstruction technique to provide deeper insights into their 3D features. Across all flow configurations arising from the different combinations of these parameters, results indicated that the bevelled nozzles are effective in introducing asymmetry to the standoff shock geometries. Depending on the exact flow configuration, standoff shock locations may also undergo significant upstream displacements. In particular, the single-bevelled nozzle produces highly unsteady standoff shocks with asymmetric oscillation amplitudes along both side of the nozzle lip regions. Changes to the standoff shock key characteristics were observed to be sensitive towards the jet shock structures and reflection point modified by the bevelled nozzle exits. In particular, the strength and relative position of the reflection point are identified as the major contributing factors influencing the upstream static pressure distribution of the standoff shock, hence leading to the observed changes in the standoff shock behaviour.
       
 
 
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