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Showing 1201 - 1400 of 2355 Journals sorted alphabetically
J. of Classification     Hybrid Journal   (Followers: 7, SJR: 0.968, h-index: 29)
J. of Clinical Geropsychology     Hybrid Journal   (Followers: 1)
J. of Clinical Immunology     Hybrid Journal   (Followers: 14, SJR: 1.332, h-index: 75)
J. of Clinical Monitoring and Computing     Hybrid Journal   (Followers: 1, SJR: 0.661, h-index: 37)
J. of Clinical Psychology in Medical Settings     Hybrid Journal   (Followers: 13, SJR: 0.46, h-index: 34)
J. of Cluster Science     Hybrid Journal   (SJR: 0.416, h-index: 31)
J. of Coal Science and Engineering (China)     Hybrid Journal   (SJR: 0.188, h-index: 8)
J. of Coastal Conservation     Hybrid Journal   (Followers: 7, SJR: 0.474, h-index: 25)
J. of Coatings Technology and Research     Hybrid Journal   (Followers: 5, SJR: 0.425, h-index: 25)
J. of Combinatorial Optimization     Hybrid Journal   (Followers: 6, SJR: 1.093, h-index: 34)
J. of Communications Technology and Electronics     Hybrid Journal   (Followers: 2, SJR: 0.29, h-index: 16)
J. of Community Genetics     Hybrid Journal   (Followers: 1, SJR: 0.727, h-index: 14)
J. of Community Health     Hybrid Journal   (Followers: 8, SJR: 0.921, h-index: 44)
J. of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology     Hybrid Journal   (Followers: 9, SJR: 1.087, h-index: 74)
J. of Comparative Physiology B : Biochemical, Systemic, and Environmental Physiology     Hybrid Journal   (Followers: 4, SJR: 1.126, h-index: 59)
J. of Compassionate Health Care     Open Access   (Followers: 3)
J. of Computational Analysis and Applications     Hybrid Journal   (SJR: 0.291, h-index: 19)
J. of Computational Electronics     Hybrid Journal   (Followers: 4, SJR: 0.511, h-index: 20)
J. of Computational Neuroscience     Hybrid Journal   (Followers: 25, SJR: 1.068, h-index: 60)
J. of Computer and Systems Sciences Intl.     Hybrid Journal   (SJR: 0.27, h-index: 13)
J. of Computer Science and Technology     Open Access   (Followers: 5, SJR: 0.437, h-index: 31)
J. of Computer Virology and Hacking Techniques     Hybrid Journal   (Followers: 6, SJR: 0.151, h-index: 2)
J. of Computer-Aided Molecular Design     Hybrid Journal   (Followers: 3, SJR: 0.995, h-index: 78)
J. of Computers in Education     Hybrid Journal   (Followers: 12)
J. of Computing in Higher Education     Hybrid Journal   (Followers: 13, SJR: 0.363, h-index: 21)
J. of Consumer Policy     Hybrid Journal   (Followers: 7, SJR: 0.704, h-index: 30)
J. of Contemporary Mathematical Analysis     Hybrid Journal   (SJR: 0.237, h-index: 5)
J. of Contemporary Physics (Armenian Academy of Sciences)     Hybrid Journal   (Followers: 11, SJR: 0.197, h-index: 6)
J. of Contemporary Psychotherapy     Hybrid Journal   (Followers: 6, SJR: 0.397, h-index: 23)
J. of Control Theory and Applications     Hybrid Journal   (Followers: 2, SJR: 0.359, h-index: 19)
J. of Control, Automation and Electrical Systems     Hybrid Journal   (Followers: 9, SJR: 0.231, h-index: 9)
J. of Crop Science and Biotechnology     Hybrid Journal   (Followers: 7)
J. of Cross-Cultural Gerontology     Hybrid Journal   (Followers: 6, SJR: 0.631, h-index: 29)
J. of Cryptographic Engineering     Partially Free   (Followers: 5, SJR: 0.989, h-index: 11)
J. of Cryptology     Hybrid Journal   (Followers: 3, SJR: 1.443, h-index: 55)
J. of Cultural Economics     Hybrid Journal   (Followers: 3, SJR: 0.539, h-index: 29)
J. of Database Marketing & Customer Strategy Management     Hybrid Journal   (Followers: 9, SJR: 0.149, h-index: 8)
J. of Derivatives & Hedge Funds     Hybrid Journal   (Followers: 8, SJR: 0.114, h-index: 5)
J. of Developmental and Physical Disabilities     Hybrid Journal   (Followers: 8, SJR: 0.574, h-index: 29)
J. of Digital Imaging     Hybrid Journal   (Followers: 9, SJR: 0.578, h-index: 35)
J. of Direct Data and Digital Marketing Practice     Hybrid Journal   (Followers: 8, SJR: 0.154, h-index: 6)
J. of Dynamical and Control Systems     Hybrid Journal   (Followers: 1, SJR: 0.4, h-index: 26)
J. of Dynamics and Differential Equations     Hybrid Journal   (SJR: 1.418, h-index: 31)
J. of Earth Science     Hybrid Journal   (Followers: 10, SJR: 0.483, h-index: 16)
J. of Earth System Science     Open Access   (Followers: 50, SJR: 0.448, h-index: 32)
J. of East Asian Linguistics     Hybrid Journal   (Followers: 7, SJR: 0.537, h-index: 20)
J. of Echocardiography     Hybrid Journal   (Followers: 5, SJR: 0.22, h-index: 3)
J. of Ecology and Environment     Open Access   (Followers: 1)
J. of Economic Growth     Hybrid Journal   (Followers: 25, SJR: 3.273, h-index: 63)
J. of Economic Interaction and Coordination     Hybrid Journal   (SJR: 0.263, h-index: 12)
J. of Economics     Hybrid Journal   (Followers: 17, SJR: 0.418, h-index: 23)
J. of Economics and Finance     Hybrid Journal   (Followers: 6, SJR: 0.272, h-index: 19)
J. of Educational Change     Hybrid Journal   (Followers: 8, SJR: 0.961, h-index: 21)
J. of Elasticity     Hybrid Journal   (Followers: 6, SJR: 0.851, h-index: 45)
J. of Electroceramics     Hybrid Journal   (SJR: 0.577, h-index: 57)
J. of Electronic Materials     Hybrid Journal   (Followers: 5, SJR: 0.609, h-index: 75)
J. of Electronic Testing     Hybrid Journal   (Followers: 2, SJR: 0.372, h-index: 27)
J. of Electronics (China)     Hybrid Journal   (Followers: 4, SJR: 0.112, h-index: 9)
J. of Elementary Science Education     Hybrid Journal   (Followers: 9)
J. of Elliptic and Parabolic Equations     Hybrid Journal  
J. of Engineering Mathematics     Hybrid Journal   (SJR: 0.347, h-index: 37)
J. of Engineering Physics and Thermophysics     Hybrid Journal   (Followers: 1, SJR: 0.288, h-index: 11)
J. of Engineering Research     Open Access   (Followers: 1, SJR: 0.145, h-index: 5)
J. of Engineering Thermophysics     Hybrid Journal   (Followers: 4, SJR: 0.763, h-index: 9)
J. of Environmental Studies and Sciences     Partially Free   (Followers: 2)
J. of Ethology     Hybrid Journal   (Followers: 2, SJR: 0.609, h-index: 25)
J. of Evolution Equations     Hybrid Journal   (SJR: 0.826, h-index: 26)
J. of Evolutionary Biochemistry and Physiology     Hybrid Journal   (SJR: 0.145, h-index: 11)
J. of Evolutionary Economics     Hybrid Journal   (Followers: 8, SJR: 0.492, h-index: 52)
J. of Experimental and Theoretical Physics     Hybrid Journal   (Followers: 3, SJR: 0.458, h-index: 39)
J. of Experimental Criminology     Hybrid Journal   (Followers: 51, SJR: 1.445, h-index: 28)
J. of Failure Analysis and Prevention     Hybrid Journal   (Followers: 5, SJR: 0.261, h-index: 15)
J. of Family and Economic Issues     Hybrid Journal   (Followers: 6, SJR: 0.396, h-index: 32)
J. of Family Violence     Hybrid Journal   (Followers: 41, SJR: 0.639, h-index: 56)
J. of Financial Services Marketing     Hybrid Journal   (Followers: 3, SJR: 0.273, h-index: 10)
J. of Financial Services Research     Hybrid Journal   (Followers: 25, SJR: 0.572, h-index: 36)
J. of Fixed Point Theory and Applications     Hybrid Journal   (SJR: 0.644, h-index: 13)
J. of Fluorescence     Hybrid Journal   (Followers: 3, SJR: 0.465, h-index: 56)
J. of Food Measurement and Characterization     Hybrid Journal   (SJR: 0.307, h-index: 4)
J. of Food Science and Technology     Hybrid Journal   (Followers: 6, SJR: 0.441, h-index: 29)
J. of Forest Research     Hybrid Journal   (Followers: 3, SJR: 0.495, h-index: 27)
J. of Forestry Research     Hybrid Journal   (Followers: 4, SJR: 0.304, h-index: 14)
J. of Fourier Analysis and Applications     Hybrid Journal   (Followers: 1, SJR: 1.18, h-index: 42)
J. of Friction and Wear     Hybrid Journal   (Followers: 7, SJR: 0.373, h-index: 7)
J. of Fusion Energy     Hybrid Journal   (Followers: 3, SJR: 0.387, h-index: 19)
J. of Gambling Studies     Hybrid Journal   (Followers: 7, SJR: 1.171, h-index: 57)
J. of Gastroenterology     Hybrid Journal   (Followers: 12, SJR: 1.651, h-index: 88)
J. of Gastrointestinal Cancer     Hybrid Journal   (Followers: 4, SJR: 0.304, h-index: 39)
J. of Gastrointestinal Surgery     Hybrid Journal   (Followers: 10, SJR: 1.64, h-index: 99)
J. of General Internal Medicine     Hybrid Journal   (Followers: 17, SJR: 1.804, h-index: 134)
J. of General Plant Pathology     Hybrid Journal   (SJR: 0.554, h-index: 22)
J. of Genetic Counseling     Hybrid Journal   (Followers: 6, SJR: 0.902, h-index: 39)
J. of Genetics     Open Access   (Followers: 5, SJR: 0.458, h-index: 28)
J. of Geodesy     Hybrid Journal   (Followers: 9, SJR: 2.173, h-index: 56)
J. of Geographical Sciences     Hybrid Journal   (Followers: 1, SJR: 0.8, h-index: 23)
J. of Geographical Systems     Hybrid Journal   (Followers: 4, SJR: 0.822, h-index: 39)
J. of Geometric Analysis     Hybrid Journal   (Followers: 2, SJR: 1.491, h-index: 27)
J. of Geometry     Hybrid Journal   (Followers: 1, SJR: 0.272, h-index: 15)
J. of Global Optimization     Hybrid Journal   (Followers: 4, SJR: 0.992, h-index: 60)
J. of Global Policy and Governance     Hybrid Journal   (Followers: 11)
J. of Grid Computing     Hybrid Journal   (Followers: 1, SJR: 1.414, h-index: 37)
J. of Happiness Studies     Hybrid Journal   (Followers: 27, SJR: 0.881, h-index: 39)
J. of Hematopathology     Hybrid Journal   (Followers: 3, SJR: 0.2, h-index: 13)
J. of Heuristics     Hybrid Journal   (Followers: 4, SJR: 1.308, h-index: 50)
J. of High Energy Physics     Hybrid Journal   (Followers: 18, SJR: 1.052, h-index: 153)
J. of Homotopy and Related Structures     Hybrid Journal   (SJR: 0.232, h-index: 2)
J. of Housing and the Built Environment     Hybrid Journal   (Followers: 7, SJR: 0.648, h-index: 28)
J. of Huazhong University of Science and Technology [Medical Sciences]     Hybrid Journal   (SJR: 0.344, h-index: 19)
J. of Ichthyology     Hybrid Journal   (Followers: 3, SJR: 0.304, h-index: 10)
J. of Immigrant and Minority Health     Hybrid Journal   (Followers: 13, SJR: 0.759, h-index: 37)
J. of Inclusion Phenomena and Macrocyclic Chemistry     Hybrid Journal   (Followers: 1, SJR: 0.331, h-index: 46)
J. of Indian Council of Philosophical Research     Hybrid Journal  
J. of Indian Philosophy     Hybrid Journal   (Followers: 12, SJR: 0.127, h-index: 12)
J. of Industrial Microbiology and Biotechnology     Hybrid Journal   (Followers: 16, SJR: 0.966, h-index: 80)
J. of Industry, Competition and Trade     Hybrid Journal   (Followers: 9, SJR: 0.327, h-index: 15)
J. of Infection and Chemotherapy     Hybrid Journal   (Followers: 2, SJR: 0.673, h-index: 46)
J. of Information Technology     Hybrid Journal   (Followers: 59, SJR: 1.474, h-index: 55)
J. of Information Technology Teaching Cases     Hybrid Journal   (Followers: 10)
J. of Infrared, Millimeter and Terahertz Waves     Hybrid Journal   (Followers: 2, SJR: 1.25, h-index: 36)
J. of Inherited Metabolic Disease     Hybrid Journal   (Followers: 2, SJR: 1.389, h-index: 77)
J. of Inorganic and Organometallic Polymers and Materials     Partially Free   (Followers: 9, SJR: 0.338, h-index: 33)
J. of Insect Behavior     Hybrid Journal   (Followers: 8, SJR: 0.569, h-index: 39)
J. of Insect Conservation     Hybrid Journal   (Followers: 10, SJR: 0.872, h-index: 43)
J. of Intelligent and Robotic Systems     Hybrid Journal   (Followers: 3, SJR: 0.629, h-index: 43)
J. of Intelligent Information Systems     Hybrid Journal   (Followers: 1, SJR: 0.691, h-index: 43)
J. of Intelligent Manufacturing     Hybrid Journal   (Followers: 3, SJR: 1.397, h-index: 54)
J. of Interventional Cardiac Electrophysiology     Hybrid Journal   (SJR: 0.93, h-index: 43)
J. of Intl. Business Studies     Hybrid Journal   (Followers: 35, SJR: 4.208, h-index: 130)
J. of Intl. Entrepreneurship     Hybrid Journal   (Followers: 10, SJR: 0.549, h-index: 23)
J. of Intl. Migration and Integration / Revue de l integration et de la migration internationale     Hybrid Journal   (Followers: 14, SJR: 0.308, h-index: 13)
J. of Intl. Relations and Development     Hybrid Journal   (Followers: 21, SJR: 0.793, h-index: 22)
J. of Labor Research     Hybrid Journal   (Followers: 20, SJR: 0.394, h-index: 27)
J. of Logic, Language and Information     Hybrid Journal   (Followers: 7, SJR: 0.288, h-index: 25)
J. of Low Temperature Physics     Hybrid Journal   (Followers: 3, SJR: 0.531, h-index: 52)
J. of Machinery Manufacture and Reliability     Hybrid Journal   (Followers: 2, SJR: 0.203, h-index: 7)
J. of Mammalian Evolution     Hybrid Journal   (Followers: 6, SJR: 1.134, h-index: 37)
J. of Mammary Gland Biology and Neoplasia     Hybrid Journal   (Followers: 2, SJR: 2.252, h-index: 83)
J. of Management and Governance     Hybrid Journal   (Followers: 14, SJR: 0.805, h-index: 33)
J. of Management Control     Hybrid Journal   (Followers: 4, SJR: 0.605, h-index: 6)
J. of Marine Science and Application     Hybrid Journal   (Followers: 2, SJR: 0.439, h-index: 11)
J. of Marine Science and Technology     Hybrid Journal   (Followers: 3, SJR: 0.235, h-index: 19)
J. of Maritime Archaeology     Hybrid Journal   (Followers: 22, SJR: 0.228, h-index: 8)
J. of Market-Focused Management     Hybrid Journal   (Followers: 2)
J. of Marketing Analytics     Hybrid Journal   (Followers: 4)
J. of Material Cycles and Waste Management     Hybrid Journal   (Followers: 3, SJR: 0.449, h-index: 22)
J. of Materials Engineering and Performance     Hybrid Journal   (Followers: 24, SJR: 0.544, h-index: 40)
J. of Materials Science     Hybrid Journal   (Followers: 21, SJR: 0.836, h-index: 123)
J. of Materials Science : Materials in Electronics     Hybrid Journal   (Followers: 6)
J. of Materials Science : Materials in Medicine     Hybrid Journal   (Followers: 5)
J. of Mathematical Biology     Hybrid Journal   (Followers: 11, SJR: 1.011, h-index: 71)
J. of Mathematical Chemistry     Hybrid Journal   (Followers: 4, SJR: 0.497, h-index: 45)
J. of Mathematical Fluid Mechanics     Hybrid Journal   (Followers: 8, SJR: 1.22, h-index: 22)
J. of Mathematical Imaging and Vision     Hybrid Journal   (Followers: 5, SJR: 0.901, h-index: 53)
J. of Mathematical Modelling and Algorithms     Hybrid Journal   (Followers: 2, SJR: 0.414, h-index: 23)
J. of Mathematical Sciences     Hybrid Journal   (SJR: 0.272, h-index: 23)
J. of Mathematics Teacher Education     Hybrid Journal   (Followers: 18, SJR: 1.062, h-index: 20)
J. of Maxillofacial and Oral Surgery     Hybrid Journal   (Followers: 3)
J. of Mechanical Science and Technology     Hybrid Journal   (Followers: 6, SJR: 0.589, h-index: 26)
J. of Medical and Biological Engineering     Hybrid Journal   (Followers: 1, SJR: 0.387, h-index: 18)
J. of Medical Humanities     Hybrid Journal   (Followers: 22, SJR: 0.299, h-index: 18)
J. of Medical Systems     Hybrid Journal   (Followers: 1, SJR: 0.717, h-index: 44)
J. of Medical Toxicology     Hybrid Journal   (Followers: 6, SJR: 0.874, h-index: 28)
J. of Medical Ultrasonics     Hybrid Journal   (Followers: 2, SJR: 0.18, h-index: 13)
J. of Medicine and the Person     Hybrid Journal  
J. of Membrane Biology     Hybrid Journal   (Followers: 2, SJR: 0.738, h-index: 82)
J. of Micro-Bio Robotics     Hybrid Journal   (SJR: 0.28, h-index: 3)
J. of Microbiology     Hybrid Journal   (Followers: 8, SJR: 0.741, h-index: 43)
J. of Mining Science     Hybrid Journal   (Followers: 4, SJR: 0.317, h-index: 16)
J. of Molecular Evolution     Hybrid Journal   (Followers: 9, SJR: 0.952, h-index: 108)
J. of Molecular Histology     Hybrid Journal   (Followers: 3, SJR: 0.755, h-index: 48)
J. of Molecular Medicine     Hybrid Journal   (Followers: 14, SJR: 2.165, h-index: 113)
J. of Molecular Modeling     Hybrid Journal   (Followers: 4, SJR: 0.466, h-index: 50)
J. of Molecular Neuroscience     Partially Free   (Followers: 11, SJR: 0.988, h-index: 69)
J. of Mountain Science     Hybrid Journal   (Followers: 3, SJR: 0.418, h-index: 15)
J. of Muscle Research and Cell Motility     Hybrid Journal   (Followers: 1, SJR: 1.264, h-index: 55)
J. of Nanoparticle Research     Hybrid Journal   (Followers: 3, SJR: 0.583, h-index: 84)
J. of Natural Medicines     Hybrid Journal   (SJR: 0.602, h-index: 28)
J. of Near-Death Studies     Hybrid Journal   (Followers: 2)
J. of Nephrology     Hybrid Journal   (Followers: 4, SJR: 0.689, h-index: 55)
J. of Network and Systems Management     Hybrid Journal   (SJR: 0.466, h-index: 26)
J. of Neural Transmission     Hybrid Journal   (Followers: 2, SJR: 1.034, h-index: 86)
J. of Neuro-Oncology     Hybrid Journal   (Followers: 3, SJR: 1.274, h-index: 90)
J. of Neuroimmune Pharmacology     Hybrid Journal   (Followers: 1, SJR: 1.662, h-index: 45)
J. of Neurology     Hybrid Journal   (Followers: 16, SJR: 1.429, h-index: 105)
J. of NeuroVirology     Hybrid Journal   (Followers: 1, SJR: 0.979, h-index: 69)
J. of Nondestructive Evaluation     Hybrid Journal   (Followers: 11, SJR: 0.863, h-index: 27)
J. of Nonlinear Science     Hybrid Journal   (Followers: 1, SJR: 1.887, h-index: 42)
J. of Nonverbal Behavior     Hybrid Journal   (Followers: 5, SJR: 0.723, h-index: 47)
J. of Nuclear Cardiology     Hybrid Journal   (SJR: 1.024, h-index: 68)
J. of Nutrition, Health and Aging     Hybrid Journal   (Followers: 26, SJR: 0.919, h-index: 60)
J. of Obstetrics and Gynecology of India     Hybrid Journal   (Followers: 5, SJR: 0.214, h-index: 6)
J. of Occupational Rehabilitation     Hybrid Journal   (Followers: 15, SJR: 0.811, h-index: 51)
J. of Ocean Engineering and Marine Energy     Hybrid Journal   (Followers: 3)
J. of Ocean University of China (English Edition)     Hybrid Journal   (Followers: 1, SJR: 0.237, h-index: 11)
J. of Oceanography     Hybrid Journal   (Followers: 10, SJR: 0.796, h-index: 52)
J. of Ocular Biology, Diseases, and Informatics     Hybrid Journal   (SJR: 0.183, h-index: 11)
J. of Optical and Fiber Communications Reports     Hybrid Journal   (Followers: 4)
J. of Optics     Hybrid Journal   (Followers: 8, SJR: 0.214, h-index: 8)
J. of Optimization Theory and Applications     Hybrid Journal   (Followers: 5, SJR: 0.898, h-index: 65)
J. of Ornithology     Hybrid Journal   (Followers: 25)

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Journal Cover Experiments in Fluids
  [SJR: 1.088]   [H-I: 82]   [13 followers]  Follow
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1432-1114 - ISSN (Online) 0723-4864
   Published by Springer-Verlag Homepage  [2355 journals]
  • Attenuation of the tip vortex flow using a flexible thread
    • Authors: Seung-Jae Lee; Jin-Woo Shin; Roger E. A. Arndt; Jung-Chun Suh
      Abstract: Abstract Tip vortex cavitation (TVC) is important in a number of practical engineering applications. The onset of TVC is a critical concern for navy surface ships and submarines that aim to increase their capability to evade detection. A flexible thread attachment at blade tips was recently suggested as a new method to delay the onset of TVC. Although the occurrence of TVC can be reduced using a flexible thread, no scientific investigation focusing on its mechanisms has been undertaken. Thus, herein, we experimentally investigated the use of the flexible thread to suppress TVC from an elliptical wing. These investigations were performed in a cavitation tunnel and involved an observation of TVC using high-speed cameras, motion tracking of the thread using image-processing techniques, and near-field flow measurements performed using stereoscopic particle image velocimetry. The experimental data suggested that the flexible thread affects the axial velocity field more than the circumferential velocity field around the TVC axis. Furthermore, we observed no clear dependence of the vortex core size, circulation, and flow unsteadiness on TVC suppression. However, the presence of the thread at the wing tip led to a notable reduction in the streamwise velocity field, thereby alleviating TVC.
      PubDate: 2017-12-29
      DOI: 10.1007/s00348-017-2476-x
      Issue No: Vol. 59, No. 1 (2017)
  • Accurate fluid force measurement based on control surface integration
    • Authors: David Lentink
      Abstract: Abstract Nonintrusive 3D fluid force measurements are still challenging to conduct accurately for freely moving animals, vehicles, and deforming objects. Two techniques, 3D particle image velocimetry (PIV) and a new technique, the aerodynamic force platform (AFP), address this. Both rely on the control volume integral for momentum; whereas PIV requires numerical integration of flow fields, the AFP performs the integration mechanically based on rigid walls that form the control surface. The accuracy of both PIV and AFP measurements based on the control surface integration is thought to hinge on determining the unsteady body force associated with the acceleration of the volume of displaced fluid. Here, I introduce a set of non-dimensional error ratios to show which fluid and body parameters make the error negligible. The unsteady body force is insignificant in all conditions where the average density of the body is much greater than the density of the fluid, e.g., in gas. Whenever a strongly deforming body experiences significant buoyancy and acceleration, the error is significant. Remarkably, this error can be entirely corrected for with an exact factor provided that the body has a sufficiently homogenous density or acceleration distribution, which is common in liquids. The correction factor for omitting the unsteady body force, \({{{ {\rho _{\text{f}}}} \mathord{\left/ {\vphantom {{1 - {\rho _{\text{f}}}} {\left( {{\rho _{\text{b}}}\;+\;{\rho _{\text{f}}}} \right)}}} \right. \kern-0pt} {\left( {{{{\rho }}_{\text{b}}}\;+\;{\rho _{\text{f}}}} \right)}}} ,\) depends only on the fluid, \({\rho _{\text{f}}}\) , and body, \({{\rho }}_{\text{b}}\) , density. Whereas these straightforward solutions work even at the liquid–gas interface in a significant number of cases, they do not work for generalized bodies undergoing buoyancy in combination with appreciable body density inhomogeneity, volume change (PIV), or volume rate-of-change (PIV and AFP). In these less common cases, the 3D body shape needs to be measured and resolved in time and space to estimate the unsteady body force. The analysis shows that accounting for the unsteady body force is straightforward to non-intrusively and accurately determine fluid force in most applications.
      PubDate: 2017-12-29
      DOI: 10.1007/s00348-017-2464-1
      Issue No: Vol. 59, No. 1 (2017)
  • Ratiometric, single-dye, pH-sensitive inhibited laser-induced fluorescence
           for the characterization of mixing and mass transfer
    • Authors: Tom Lacassagne; Serge Simoëns; Mahmoud El Hajem; Jean-Yves Champagne
      Abstract: Abstract Inhibited planar laser-induced fluorescence (I-PLIF) techniques are widely used for heat and mass transfer studies in fluid mechanics. They allow the visualization of instantaneous two-dimensional field of a passive or reactive scalar, providing that this scalar acts as an inhibitor to the fluorescence of a specific molecule, and that this molecule is homogeneously mixed in the fluid at a known concentration. Local scalar values are deduced from fluorescence recordings thanks to preliminary calibration procedure. When confronted with non-optically thin systems, however, the knowledge of the excitation intensity distribution in the region of interest is also required, and this information is most of the time hard to obtain. To overcome that problem, two-color ratiometric PLIF techniques ( \(\text {I}^\text {r}\) -PLIF) have been developed. In these methods, the ratio of two different fluorescence wavelengths triggered by the same excitation is used as an indicator of the scalar value. Such techniques have been used for temperature measurements in several studies but never, to the author’s knowledge, for pH tracking and acid–base mixing, despite the frequent use of the one-color version in mass transfer studies. In the present work, a ratiometric pH-sensitive-inhibited PLIF technique ( \(\text {I}_\text {pH}^\text {r}\) -PLIF) using fluorescein sodium as a single dye and applicable to complex geometries and flows is developed. Theoretical considerations show that the ratio of the two-color fluorescence intensities should only depend on the dye’s spectral quantum yield, itself pH-dependent. A detailed spectrofluorimetric study of fluorescein reveals that this ratio strictly increases with the pH for two well-chosen spectral bands (fluorescence colors). A similar trend is found when using sCmos cameras equipped with optical filters to record fluorescence signals. The method is then experimented on a test flow, a turbulent acidic jet injected in an initially pH-neutral volume of fluid. The results obtained using the ratiometric version are consistent with single-color technique measurements, but excitation intensity heterogeneity is more efficiently accounted for, with a much smaller time needed for data treatment and without requiring the knowledge of laser paths across the fluid. This new technique is also able to reduce the impact of some unwanted experimental features such as time-varying excitation intensity or reflections at interfaces. It can be of great interest for further applications to multiphase mass transfer studies.
      PubDate: 2017-12-21
      DOI: 10.1007/s00348-017-2475-y
      Issue No: Vol. 59, No. 1 (2017)
  • Evolution of the bi-stable wake of a square-back automotive shape
    • Authors: Giancarlo Pavia; Martin Passmore; Costantino Sardu
      Abstract: Abstract Square-back shapes are popular in the automotive market for their high level of practicality. These geometries, however, are usually characterised by high drag and their wake dynamics present aspects, such as the coexistence of a long-time bi-stable behaviour and short-time global fluctuating modes that are not fully understood. In the present paper, the unsteady behaviour of the wake of a generic square-back car geometry is characterised with an emphasis on identifying the causal relationship between the different dynamic modes in the wake. The study is experimental, consisting of balance, pressure, and stereoscopic PIV measurements. Applying wavelet and cross-wavelet transforms to the balance data, a quasi-steady correlation is demonstrated between the forces and bi-stable modes. This is investigated by applying proper orthogonal decomposition to the pressure and velocity data sets and a new structure is proposed for each bi-stable state, consisting of a hairpin vortex that originates from one of the two model’s vertical trailing edges and bends towards the opposite side as it merges into a single streamwise vortex downstream. The wake pumping motion is also identified and for the first time linked with the motion of the bi-stable vortical structure in the streamwise direction, resulting in out-of-phase pressure variations between the two vertical halves of the model base. A phase-averaged low-order model is also proposed that provides a comprehensive description of the mechanisms of the switch between the bi-stable states. It is demonstrated that, during the switch, the wake becomes laterally symmetric and, at this point, the level of interaction between the recirculating structures and the base reaches a minimum, yielding, for this geometry, a \(7\%\) reduction of the base drag compared to the time-averaged result.
      PubDate: 2017-12-21
      DOI: 10.1007/s00348-017-2473-0
      Issue No: Vol. 59, No. 1 (2017)
  • A Lagrangian perspective towards studying entrainment
    • Authors: Giuseppe A. Rosi; David E. Rival
      Abstract: Abstract This study presents a method for characterizing entrainment using Lagrangian data. Specifically, the method exploits the temporal evolution of enstrophy along pathlines to determine if pathlines undergo entrainment. The method only recently became feasible with the development of four-dimensional particle tracking velocimetry [4D-PTV; see Schanz et al. (Exp Fluids 57(5):7, 2016)], which produces pathlines of temporal length and spatial density that was previously unattainable. The proposed entrainment method was tested on experimentally acquired 4D-PTV data of a turbulent starting vortex forming behind a linearly accelerating circular plate. The method is shown to be insensitive to its control parameters. The first control parameter is an enstrophy threshold used to identify pathlines that always exhibit low enstrophy. The second control parameter is the size of an “enstrophy-source region”, which is placed within the measurement domain to identify pathlines that gain enstrophy through interactions with an enstrophy source. In the case of the starting vortex, the method reveals topological features significant to the entrainment process, such as the roll-up of irrotational fluid between the shear layer and vortex core, and pockets of entrainment that exist within undulations on the shear layer’s outboard side. Whereas the method proposed here measures the entrainment ratio directly, the use of Lagrangian coherent structures (LCSs) to quantify entrainment is shown to be infeasible for turbulent flows due to the presence of complex material manifolds for such flows. Furthermore, unlike results from Rosi and Rival (J Fluid Mech 811:3750, 2017), which analyzed the spreading of enstrophy isocontours to characterize entrainment into a starting vortex, the proposed method produces an entrainment rate that is insensitive to the enstrophy threshold, and clearly reveals mechanisms of entrainment. Using the starting vortex data, the proposed technique measured an entrainment ratio range similar to that for laminar vortex rings. The result suggests that, for this particular class of flows, turbulence does not play a significant role with respect to entrainment. The proposed method is seen as an effective tool, given its ability to quantify the entrainment, reveal its salient topological features, and potentially be easily adapted to other classes of flows.
      PubDate: 2017-12-21
      DOI: 10.1007/s00348-017-2465-0
      Issue No: Vol. 59, No. 1 (2017)
  • The dynamics of milk droplet–droplet collisions
    • Authors: Giulia Finotello; Roeland F. Kooiman; Johan T. Padding; Kay A. Buist; Alfred Jongsma; Fredrik Innings; J. A. M. Kuipers
      Abstract: Abstract Spray drying is an important industrial process to produce powdered milk, in which concentrated milk is atomized into small droplets and dried with hot gas. The characteristics of the produced milk powder are largely affected by agglomeration, combination of dry and partially dry particles, which in turn depends on the outcome of a collision between droplets. The high total solids (TS) content and the presence of milk proteins cause a relatively high viscosity of the fed milk concentrates, which is expected to largely influence the collision outcomes of drops inside the spray. It is therefore of paramount importance to predict and control the outcomes of binary droplet collisions. Only a few studies report on droplet collisions of high viscous liquids and no work is available on droplet collisions of milk concentrates. The current study therefore aims to obtain insight into the effect of viscosity on the outcome of binary collisions between droplets of milk concentrates. To cover a wide range of viscosity values, three milk concentrates (20, 30 and \(46\%\) TS content) are investigated. An experimental set-up is used to generate two colliding droplet streams with consistent droplet size and spacing. A high-speed camera is used to record the trajectories of the droplets. The recordings are processed by Droplet Image Analysis in MATLAB to determine the relative velocities and the impact geometries for each individual collision. The collision outcomes are presented in a regime map dependent on the dimensionless impact parameter and Weber (We) number. The Ohnesorge (Oh) number is introduced to describe the effect of viscosity from one liquid to another and is maintained constant for each regime map by using a constant droplet diameter (d \(\sim 700\ \upmu \hbox {m}\) ). In this work, a phenomenological model is proposed to describe the boundaries demarcating the coalescence-separation regimes. The collision dynamics and outcome of milk concentrates are compared with aqueous glycerol solutions experiments. While milk concentrates have complex chemical composition and rheology, glycerol solutions are Newtonian fluids and therefore easy to characterize. The collision morphologies of glycerol solutions and milk concentrates are similar, and the regime maps can be described by the same phenomenological model developed in this work. The regime of bouncing, however, was not observed for any of the milk concentrates.
      PubDate: 2017-12-12
      DOI: 10.1007/s00348-017-2471-2
      Issue No: Vol. 59, No. 1 (2017)
  • Time-resolved flow reconstruction with indirect measurements using
           regression models and Kalman-filtered POD ROM
    • Authors: Romain Leroux; Ludovic Chatellier; Laurent David
      Abstract: Abstract This article is devoted to the estimation of time-resolved particle image velocimetry (TR-PIV) flow fields using a time-resolved point measurements of a voltage signal obtained by hot-film anemometry. A multiple linear regression model is first defined to map the TR-PIV flow fields onto the voltage signal. Due to the high temporal resolution of the signal acquired by the hot-film sensor, the estimates of the TR-PIV flow fields are obtained with a multiple linear regression method called orthonormalized partial least squares regression (OPLSR). Subsequently, this model is incorporated as the observation equation in an ensemble Kalman filter (EnKF) applied on a proper orthogonal decomposition reduced-order model to stabilize it while reducing the effects of the hot-film sensor noise. This method is assessed for the reconstruction of the flow around a NACA0012 airfoil at a Reynolds number of 1000 and an angle of attack of \({20}^{\circ }\) . Comparisons with multi-time delay-modified linear stochastic estimation show that both the OPLSR and EnKF combined with OPLSR are more accurate as they produce a much lower relative estimation error, and provide a faithful reconstruction of the time evolution of the velocity flow fields.
      PubDate: 2017-12-12
      DOI: 10.1007/s00348-017-2455-2
      Issue No: Vol. 59, No. 1 (2017)
  • Interaction of a trailing vortex with an oscillating wing
    • Authors: C. McKenna; G. Fishman; D. Rockwell
      Abstract: Abstract A technique of particle image velocimetry is employed to characterize the flow structure of a trailing vortex incident upon the tip region of an oscillating wing (plate). The amplitude and velocity of the wing are nearly two orders of magnitude smaller than the wing chord and free stream velocity, respectively. Depending upon the outboard displacement of the incident vortex relative to the wing tip, distinctive patterns of upwash, downwash, and shed vorticity are observed. These patterns are a strong function of the phase of the wing motion during its oscillation cycle. At a given phase, the wing oscillation induces upwash that is reinforced by the upwash of the incident vortex, giving a maximum net upwash. Conversely, when these two origins of upwash counteract, rather than reinforce, one another during the oscillation cycle, the net upwash attains minimum value. Analogous interpretations hold for regions of maximum and minimum net downwash located outboard of the regions of upwash. The magnitude and scale of the vorticity shed from the tip of the wing are directly correlated with the net upwash, which takes different forms related to the outboard displacement of the incident vortex. As the location of the incident vortex is displaced towards the wing tip, both the maximum upwash and the maximum vorticity of the tip vortex initially increase and then decrease. For the limiting case where the incident vortex impinges directly upon the tip of the wing, there is no tip vortex or induced region of upwash. Furthermore, at small values of vortex displacement from the wing tip, the position of the incident vortex varies significantly from its nominal position during the oscillation cycle. All of the foregoing features are interpreted in conjunction with the flow topology in the form of streamlines and critical points, superposed on patterns of vorticity. It is shown that despite the small amplitude of the wing motion, the flow topology is fundamentally different at maximum positive and negative values of the velocity of the wing tip, that is, they are not symmetric.
      PubDate: 2017-12-12
      DOI: 10.1007/s00348-017-2474-z
      Issue No: Vol. 59, No. 1 (2017)
  • Aeroacoustic analysis of the human phonation process based on a hybrid
           acoustic PIV approach
    • Authors: Alexander Lodermeyer; Matthias Tautz; Stefan Becker; Michael Döllinger; Veronika Birk; Stefan Kniesburges
      Abstract: Abstract The detailed analysis of sound generation in human phonation is severely limited as the accessibility to the laryngeal flow region is highly restricted. Consequently, the physical basis of the underlying fluid–structure–acoustic interaction that describes the primary mechanism of sound production is not yet fully understood. Therefore, we propose the implementation of a hybrid acoustic PIV procedure to evaluate aeroacoustic sound generation during voice production within a synthetic larynx model. Focusing on the flow field downstream of synthetic, aerodynamically driven vocal folds, we calculated acoustic source terms based on the velocity fields obtained by time-resolved high-speed PIV applied to the mid-coronal plane. The radiation of these sources into the acoustic far field was numerically simulated and the resulting acoustic pressure was finally compared with experimental microphone measurements. We identified the tonal sound to be generated downstream in a small region close to the vocal folds. The simulation of the sound propagation underestimated the tonal components, whereas the broadband sound was well reproduced. Our results demonstrate the feasibility to locate aeroacoustic sound sources inside a synthetic larynx using a hybrid acoustic PIV approach. Although the technique employs a 2D-limited flow field, it accurately reproduces the basic characteristics of the aeroacoustic field in our larynx model. In future studies, not only the aeroacoustic mechanisms of normal phonation will be assessable, but also the sound generation of voice disorders can be investigated more profoundly.
      PubDate: 2017-12-06
      DOI: 10.1007/s00348-017-2469-9
      Issue No: Vol. 59, No. 1 (2017)
  • Development of $${\rm N}_2{\rm O}$$ N 2 O -MTV for low-speed flow and
           in-situ deployment to an integral effect test facility
    • Authors: Matthieu A. André; Ross A. Burns; Paul M. Danehy; Seth R. Cadell; Brian G. Woods; Philippe M. Bardet
      Abstract: Abstract A molecular tagging velocity (MTV) technique is developed to non-intrusively measure velocity in an integral effect test (IET) facility simulating a high-temperature helium-cooled nuclear reactor in accident scenarios. In these scenarios, the velocities are expected to be low, on the order of 1 m/s or less, which forces special requirements on the MTV tracer selection. Nitrous oxide \(({\rm N}_2{\rm O})\) is identified as a suitable seed gas to generate NO tracers capable of probing the flow over a large range of pressure, temperature, and flow velocity. The performance of \({\rm N}_2{\rm O}\) -MTV is assessed in the laboratory at temperature and pressure ranging from 295 to 781 K and 1 to 3 atm. MTV signal improves with a temperature increase, but decreases with a pressure increase. Velocity precision down to 0.004 m/s is achieved with a probe time of 40 ms at ambient pressure and temperature. Measurement precision is limited by tracer diffusion, and absorption of the tag laser beam by the seed gas. Processing by cross-correlation of single-shot images with high signal-to-noise ratio reference images improves the precision by about 10% compared to traditional single-shot image correlations. The instrument is then deployed to the IET facility. Challenges associated with heat, vibrations, safety, beam delivery, and imaging are addressed in order to successfully operate this sensitive instrument in-situ. Data are presented for an isothermal depressurized conduction cooldown. Velocity profiles from MTV reveal a complex flow transient driven by buoyancy, diffusion, and instability taking place over short \((<1\, {\rm s})\) and long ( \(>30\) min) time scales at sub-meter per second speed. The precision of the in-situ results is estimated at 0.027, 0.0095, and 0.006 m/s for a probe time of 5, 15, and 35 ms, respectively.
      PubDate: 2017-12-06
      DOI: 10.1007/s00348-017-2470-3
      Issue No: Vol. 59, No. 1 (2017)
  • Bubble nucleation from micro-crevices in a shear flow
    • Authors: T. F. Groß; J. Bauer; G. Ludwig; D. Fernandez Rivas; P. F. Pelz
      Abstract: Abstract The formation of gas bubbles at gas cavities located in walls bounding the flow occurs in many technical applications, but is usually hard to observe. Even though, the presence of a fluid flow undoubtedly affects the formation of bubbles, there are very few studies that take this fact into account. In the present paper new experimental results on bubble formation (diffusion-driven nucleation) from surface nuclei in a shear flow are presented. The observed gas-filled cavities are micrometre-sized blind holes etched in silicon substrates. We measure the frequency of bubble generation (nucleation rate), the size of the detaching bubbles and analyse the growth of the surface nuclei. The experimental findings support an extended understanding of bubble formation as a self-excited cyclic process and can serve as validation data for analytical and numerical models.
      PubDate: 2017-12-06
      DOI: 10.1007/s00348-017-2459-y
      Issue No: Vol. 59, No. 1 (2017)
  • Investigation of shock–acoustic-wave interaction in transonic flow
    • Authors: Antje Feldhusen-Hoffmann; Vladimir Statnikov; Michael Klaas; Wolfgang Schröder
      Abstract: Abstract The buffet flow field around supercritical airfoils is dominated by self-sustained shock wave oscillations on the suction side of the wing. Theories assume that this unsteadiness is driven by an acoustic feedback loop of disturbances in the flow field downstream of the shock wave whose upstream propagating part is generated by acoustic waves. Therefore, in this study, first variations in the sound pressure level of the airfoil’s trailing-edge noise during a buffet cycle, which force the shock wave to move upstream and downstream, are detected, and then, the sensitivity of the shock wave oscillation during buffet to external acoustic forcing is analyzed. Time-resolved standard and tomographic particle-image velocimetry (PIV) measurements are applied to investigate the transonic buffet flow field over a supercritical DRA 2303 airfoil. The freestream Mach number is \(M_{\infty } = 0.73\) , the angle of attack is \(\alpha = {3.5}^{\circ }\) , and the chord-based Reynolds number is \(Re_c = 1.9\times 10^6\) . The perturbed Lamb vector field, which describes the major acoustic source term of trailing-edge noise, is determined from the tomographic PIV data. Subsequently, the buffet flow field is disturbed by an artificially generated acoustic field, the acoustic intensity of which is comparable to the Lamb vector that is determined from the PIV data. The results confirm the hypothesis that buffet is driven by an acoustic feedback loop and show the shock wave oscillation to directly respond to external acoustic forcing. That is, the amplitude modulation frequency of the artificial acoustic perturbation determines the shock oscillation.
      PubDate: 2017-12-06
      DOI: 10.1007/s00348-017-2466-z
      Issue No: Vol. 59, No. 1 (2017)
  • An experimental study of wall-injected flows in a rectangular cylinder
    • Authors: A. Perrotta; G. P. Romano; B. Favini
      Abstract: Abstract An experimental investigation of the flow inside a rectangular cylinder with air injected continuously along the wall is performed. This kind of flow is a two-dimensional approximation of what happens inside a solid rocket motor, where the lateral grain burns expelling exhaust gas or in processes with air filtration or devices to attain uniform flows. We propose a brief derivation of some analytical solutions and a comparison between these solutions and experimental data, which are obtained using the particle image velocimetry technique, to provide a global reconstruction of the flowfield. The flow, which enters orthogonal to the injecting wall, turns suddenly its direction being pushed towards the exit of the chamber. Under the incompressible and inviscid flow hypothesis, two analytical solutions are reported and compared. The first one, known as Hart–McClure solution, is irrotational and the injection velocity is non-perpendicular to the injecting wall. The other one, due to Taylor and Culick, has non-zero vorticity and constant, vertical injection velocity. The comparison with laminar solutions is useful to assess whether transition to turbulence is reached and how the disturbance thrown in by the porous injection influences and modifies those solutions.
      PubDate: 2017-12-06
      DOI: 10.1007/s00348-017-2472-1
      Issue No: Vol. 59, No. 1 (2017)
  • Multi-camera volumetric PIV for the study of jumping fish
    • Authors: Leah Mendelson; Alexandra H. Techet
      Abstract: Abstract Archer fish accurately jump multiple body lengths for aerial prey from directly below the free surface. Multiple fins provide combinations of propulsion and stabilization, enabling prey capture success. Volumetric flow field measurements are crucial to characterizing multi-propulsor interactions during this highly three-dimensional maneuver; however, the fish’s behavior also drives unique experimental constraints. Measurements must be obtained in close proximity to the water’s surface and in regions of the flow field which are partially-occluded by the fish body. Aerial jump trajectories must also be known to assess performance. This article describes experiment setup and processing modifications to the three-dimensional synthetic aperture particle image velocimetry (SAPIV) technique to address these challenges and facilitate experimental measurements on live jumping fish. The performance of traditional SAPIV algorithms in partially-occluded regions is characterized, and an improved non-iterative reconstruction routine for SAPIV around bodies is introduced. This reconstruction procedure is combined with three-dimensional imaging on both sides of the free surface to reveal the fish’s three-dimensional wake, including a series of propulsive vortex rings generated by the tail. In addition, wake measurements from the anal and dorsal fins indicate their stabilizing and thrust-producing contributions as the archer fish jumps.
      PubDate: 2017-12-04
      DOI: 10.1007/s00348-017-2468-x
      Issue No: Vol. 59, No. 1 (2017)
  • Behaviour of the energy dissipation coefficient in a rough wall turbulent
           boundary layer
    • Authors: Md. Kamruzzaman; L. Djenidi; R. A. Antonia
      Abstract: Abstract Hot-wire anemometry measurements are made in a rough wall turbulent boundary layer to assess the dependence of the mean turbulent kinetic energy dissipation coefficient, \(C_\varepsilon\) , on the distance from the wall and the Taylor microscale Reynolds number, \(Re_\lambda\) . The locally isotropic expression \(\langle \varepsilon _\mathrm{{iso}}\rangle\) is used as a surrogate for the mean turbulent kinetic energy dissipation rate, \(\langle \varepsilon \rangle\) , for calculating \(C_\varepsilon =\langle \varepsilon \rangle L/u^{\prime 3}\) ; L and \(u'\) are the integral length scale and the rms of the longitudinal velocity fluctuation, respectively. The measurements show that \(C_\varepsilon\) varies significantly near the wall, but becomes almost constant in the region \(0.2 \le y/\delta \le 0.6\) of the boundary layer, a region where \(Re_\lambda\) is also practically constant.
      PubDate: 2017-12-01
      DOI: 10.1007/s00348-017-2467-y
      Issue No: Vol. 59, No. 1 (2017)
  • Immiscible impact dynamics of droplets onto millimetric films
    • Authors: S. Shaikh; G. Toyofuku; R. Hoang; J. O. Marston
      Abstract: Abstract The impact of liquid droplets onto a film of an immiscible liquid is studied experimentally across a broad range of parameters [ \(Re = O(10^{1}-10^{3})\) , \(We = O(10^{2}-10^{3})\) ] with the aid of high-speed photography and image analysis. Above a critical impact parameter, \(Re^{1/2}We^{1/4} \approx 100\) , the droplet fragments into multiple satellite droplets, which typically occurs as the result of a fingering instability. Statistical analysis indicates that the satellite droplets are approximately log-normally distributed, in agreement with some previous studies and the theoretical predictions of Wu (Prob Eng Mech 18:241–249, 2003). However, in contrast to a recent study by Lhuissier et al. (Phys Rev Lett 110:264503, 2013), we find that it is the modal satellite diameter, not the mean diameter, that scales inversely with the impact speed (or Weber number) and that the dependence is \(d_\mathrm{{mod}} \sim We^{-1/4}\) .
      PubDate: 2017-11-29
      DOI: 10.1007/s00348-017-2461-4
      Issue No: Vol. 59, No. 1 (2017)
  • Motion estimation under location uncertainty for turbulent fluid flows
    • Authors: Shengze Cai; Etienne Mémin; Pierre Dérian; Chao Xu
      Abstract: Abstract In this paper, we propose a novel optical flow formulation for estimating two-dimensional velocity fields from an image sequence depicting the evolution of a passive scalar transported by a fluid flow. This motion estimator relies on a stochastic representation of the flow allowing to incorporate naturally a notion of uncertainty in the flow measurement. In this context, the Eulerian fluid flow velocity field is decomposed into two components: a large-scale motion field and a small-scale uncertainty component. We define the small-scale component as a random field. Subsequently, the data term of the optical flow formulation is based on a stochastic transport equation, derived from the formalism under location uncertainty proposed in Mémin (Geophys Astrophys Fluid Dyn 108(2):119–146, 2014) and Resseguier et al. (Geophys Astrophys Fluid Dyn 111(3):149–176, 2017a). In addition, a specific regularization term built from the assumption of constant kinetic energy involves the very same diffusion tensor as the one appearing in the data transport term. Opposite to the classical motion estimators, this enables us to devise an optical flow method dedicated to fluid flows in which the regularization parameter has now a clear physical interpretation and can be easily estimated. Experimental evaluations are presented on both synthetic and real world image sequences. Results and comparisons indicate very good performance of the proposed formulation for turbulent flow motion estimation.
      PubDate: 2017-11-29
      DOI: 10.1007/s00348-017-2458-z
      Issue No: Vol. 59, No. 1 (2017)
  • Modeling of a pitching and plunging airfoil using experimental flow field
           and load measurements
    • Authors: Victor Troshin; Avraham Seifert
      Abstract: Abstract The main goal of the current paper is to outline a low-order modeling procedure of a heaving airfoil in a still fluid using experimental measurements. Due to its relative simplicity, the proposed procedure is applicable for the analysis of flow fields within complex and unsteady geometries and it is suitable for analyzing the data obtained by experimentation. Currently, this procedure is used to model and predict the flow field evolution using a small number of low profile load sensors and flow field measurements. A time delay neural network is used to estimate the flow field. The neural network estimates the amplitudes of the most energetic modes using four sensory inputs. The modes are calculated using proper orthogonal decomposition of the flow field data obtained experimentally by time-resolved, phase-locked particle imaging velocimetry. To permit the use of proper orthogonal decomposition, the measured flow field is mapped onto a stationary domain using volume preserving transformation. The analysis performed by the model showed good estimation quality within the parameter range used in the training procedure. However, the performance deteriorates for cases out of this range. This situation indicates that, to improve the robustness of the model, both the decomposition and the training data sets must be diverse in terms of input parameter space. In addition, the results suggest that the property of volume preservation of the mapping does not affect the model quality as long as the model is not based on the Galerkin approximation. Thus, it may be relaxed for cases with more complex geometry and kinematics.
      PubDate: 2017-11-28
      DOI: 10.1007/s00348-017-2462-3
      Issue No: Vol. 59, No. 1 (2017)
  • Superheated liquid carbon dioxide jets: setting up and phenomena
    • Authors: Lena Engelmeier; Stefan Pollak; Franz Peters; Eckhard Weidner
      Abstract: Abstract We present an experimental investigation on liquid, superheated carbon dioxide jets. Our main goal is to identify the setting up requirements for generating coherent jets because these raise expectations on applications in the cleaning and cutting industry. The study leads us through a number of phenomena, which are described, categorized and explained. The experiments are based on compressed (350 MPa) and cooled carbon dioxide, which expands through a cylindrical nozzle into the atmosphere. The nozzle provokes hydraulic flip by a sharp-edge inlet leading to separation and constriction. Upstream-temperature and pressure are varied and the jet’s structure and phase state are monitored by a high-speed camera. We observe coherent, liquid jets far from equilibrium, which demands the solid or gaseous state. Therefore, these jets are superheated. Carbon dioxide jets, like water jets, below certain nozzle diameters are subject to fluid dynamic instabilities resulting in breakup. Above certain diameters flashing jet breakup appears, which is associated with nucleation.
      PubDate: 2017-11-25
      DOI: 10.1007/s00348-017-2463-2
      Issue No: Vol. 59, No. 1 (2017)
  • Quantification of Marangoni flows and film morphology during solid film
           formation by inkjet printing
    • Authors: Hirotaka Ishizuka; Jun Fukai
      Abstract: Abstract We visualized experimentally the internal flow inside inkjet droplets of polystyrene–anisole solution during solid film formation on substrates at room temperature. The effects of contact angle and evaporation rate on the internal flow and film morphology were quantitatively investigated. The transport process during film formation was examined by measuring the relationship between internal flow and film morphology, which provided three remarkable findings. First, self-pinning and the strength of outward flow on the free surface under 2.3 Pa s determined film morphology. The solute distribution, corresponding to rim areas in ring-like films and a convex trough in dot-like films, had already developed at self-pinning. Second, the mass fraction at self-pinning close to the contact line converged to one, regardless of the film morphology. This implies that self-pinning is independent of parameters such as the contact angle and evaporation rate. Third, at room temperature, the solutal Marangoni numbers were 20–30 times larger than the thermal ones. Thus, the outward flow on the free surface caused by the solutal Marangoni effect dominates in droplets before self-pinning. The solutal Marangoni number at self-pinning and thickness variation at the center of the film displayed a good relationship for droplets with different contact angles and evaporation rates. This suggests that film morphology can be technically controlled by solutal Marangoni number at room temperature.
      PubDate: 2017-11-25
      DOI: 10.1007/s00348-017-2460-5
      Issue No: Vol. 59, No. 1 (2017)
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