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Aerospace Science and Technology
Journal Prestige (SJR): 0.796
Citation Impact (citeScore): 3
Number of Followers: 333  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1270-9638
Published by Elsevier Homepage  [3162 journals]
  • Unsteady behavior of oblique shock train and boundary layer interactions
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Chengpeng Wang, Chuan Cheng, Keming Cheng, Longsheng Xue The aim of present investigation is to analyze the unsteady oblique shock train and boundary layer interactions during the self-excited and forced oscillation. The oblique shock train is generated in a Mach 2.7 ducted flow and controlled by a downstream elliptical shaft. Cyclic rotating of the shaft leads to the forced oscillation. A Schlieren system as well as transient pressure measurements and particle image velocimetry have been used to capture quantitative and qualitative shock structure information. Results show that the behaviors of unsteady SBLIs structure are highly related to the dynamics of shock motion. For both self-excited oscillation and forced oscillation, the asymmetrical characteristics of first X-shock was found to be negatively correlated with shock velocity. There exist some relative motions between the first X-shock and the second shock, but the absolute variations are very weak. At lower excitation frequency, the relative motion is not noticeable to the oscillation amplitude, it could be treated as a rigid motion in the duct. At higher excitation frequency, the relative motion amplitude is significant to the oscillation amplitude, and the relative movement of shock cells becomes the dominant motion. There is a hysteretic effect and phase lag between the shock position and downstream pressure perturbation when the shock train travels along a different path for upstream and downstream movements, and the hysteretic effect becomes weaker with increasing frequency.
       
  • Eco-efficiency assessment of manufacturing carbon fiber reinforced
           polymers (CFRP) in aerospace industry
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Ali Al-Lami, Philipp Hilmer, Michael Sinapius Carbon fiber reinforced polymers (CFRP) are frequently used in aerospace industry. However, the manufacturing carbon footprint and direct cost are obstacles in the way of adopting CFRP in further aerospace structures. Therefore, the development of a combined ecological and economic assessment model for CFRP manufacturing is demonstrated in this paper. This model illuminates the proper developments for the decision-makers.In this work, the eco-efficiency assessment model (EEAM) is developed based on life cycle assessment (LCA) and life cycle cost analysis (LCCA). EEAM is an activity-based bottom-up decision support tool for the manufacturing process of fiber reinforced polymer (FRP). This paper discuses a case study of manufacturing CFRP wing ribs for a modern commercial aircraft as a part of the project LOCOMACHS.Ecological results of EEAM conclude that the carbon footprint of manufacturing wing rib made of CFRP thermoset by the technique of in-autoclave single-line-injection (SLI) is around 109 kg CO2-equivalent for each kg of CFRP. Moreover, fiber material is the main contributor in this carbon footprint. On the other hand, the economic assessment shows that the studied rib has a direct manufacturing cost of about 584 €/kg. In these results, labor work dominates the direct cost with 49%, while fiber and matrix compensate about 35%.As an activity-based assessment model, EEAM guides the decision-makers toward sustainable direct applications. It is concluded that direct applications for fiber waste reduction are beneficial for both eco-efficiency aspects. Energy consumption reduction is ecologically beneficial, while labor work reduction on the other hand is cost relevant. In aerospace industry, there is a clear potential for eco-efficient direct applications that satisfy both aspects.
       
  • Substructure-based distributed collaborative probabilistic analysis method
           for low-cycle fatigue damage assessment of turbine blade–disk
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Haifeng Gao, Anjenq Wang, Guangchen Bai, Chunmei Wei, Chengwei Fei A numerical simulation-based probabilistic analysis methodology, substructure-based distributed collaborative probabilistic analysis method (SDCPAM), is proposed for accurate and efficient fatigue prognosis based on distributed collaborative response surface method (DCRSM) and substructure analysis method. This paper focuses on the low-cycle fatigue (LCF) damage assessment for turbine blade–disk system. Based on the established probabilistic strain–life models and fatigue reliability model for tandem system, the LCF damage principle of turbine blade–disk system is proposed and integrated with SDCPAM. Following that, the LCF life prediction of the turbine blade–disk is completed, and probabilistic sensitivity analyses of blade and disk to the LCF life of the turbine blade–disk system are achieved. According to the above efforts, the feasibility and effectiveness of SDCPAM is verified. Finally, the LCF damage assessment for the blade–disk system is accomplished, and the influences of applied cycle and reliability level on the LCF damage are investigated. Through the comparisons of the proposed with traditional fatigue reliability model, it is illustrated that the proposed fatigue reliability model is reasonable. The results show that blade and disk almost have the same great influence on the blade–disk LCF life. In addition, applied cycles under normal and lognormal distributions produce the same LCF damage reliability that decreases with increasing applied cycle and reliability level. The efforts of this study indicate the reasonability of the proposed method and models in describing the LCF damage reliability of the blade–disk system, and enrich the reliability theory and method for the complex structure with multi-component and multi-failure mode.
       
  • Gust response stabilization for rigid aircraft with
           multi-control-effectors based on a novel integrated control scheme
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Jinglong Liu, Weiguo Zhang, Xiaoxiong Liu, Qizhi He, Yunxiao Qin For the higher performance demand of aircraft, the active control techniques of flight control system become more attractive. Among these approaches, the gust response stabilization has been more significant for the consideration of safety and comfort. Due to the constraint of the traditional control law, the parameter tuning process in a large envelope is very time-consuming and some special maneuvers can't accomplish by these designs. In order to overcome these defects of the conventional flight control laws, a new integrated nonlinear control scheme with modified active disturbance rejection control and real-time direct lift compensation control allocation technology is proposed. Its switched extended state observer can bring the observers to their full talents to estimate the signals. Aiming at taking full potential of the multi-control-effectors aircraft, two real-time linear control allocation methods for the transition from virtual control variables to actual control variables are also introduced. The simulation showed that this structure has good tracking performance and wind resistance performance.
       
  • Characteristics and model of the initial spray caused by an aircraft
           elastic tire rolling on the water-contaminated runway
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Yujia Zhang, Peiqing Liu, Qiulin Qu, Ting Liu, Tianxiang Hu The initial spray caused by a rolling aircraft elastic pneumatic tire is studied by Smoothed Particle Hydrodynamics method. The tire spray is divided into four types: bow wave, rooster tail, impact-generated side plume and wave-generated side plume. The distributions of the particles involved in the different types of spray in the initial unperturbed water film are studied, with the relationship between the momentum transfer, the relative position of water particles and the aircraft tire being proposed. The impact-generated side plume is caused by the direct impact of tire, while the wave-generated side plume is caused by the breakup of the wave developed by the tire. The particles involved in the wave-generated side plume all come from a parabolic region inside the strip of initial injected particles at a given time. The width of the parabolic region reduces with the increasing water depth. The strips and the kinematic characteristics of particles at any time are both similar. A model is developed to predict the direction and magnitude of the momentum transfer velocity in water film based on the similarity of the strips and the kinematic characteristics of the particles, which works well for the cases with small tire load and thick water film.
       
  • A novel control scheme for quadrotor UAV based upon active disturbance
           rejection control
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Yong Zhang, Zengqiang Chen, Xinghui Zhang, Qinglin Sun, Mingwei Sun A double closed-loop active disturbance rejection control (ADRC) scheme is proposed to deal with some difficult control problems in the quadrotor unmanned aerial vehicle (UAV) system such as nonlinearity, strong coupling and sensitive to disturbance, etc. Firstly, the virtual control variables are introduced to decouple the quadrotor flight system that can simplify the mathematical model of the system. Secondly, the extended state observer (ESO) is used to estimate and compensate the internal uncertainties and external disturbances in real time which can improve the robustness and anti-disturbance ability of the system. Finally, the stability of the system is proved. The simulation results show that the control scheme proposed in this paper can ensure that the quadrotor track the target trajectory quickly and accurately while maintaining stability, even with external disturbances.
       
  • Finite-time model-assisted active disturbance rejection control with a
           novel parameters optimizer for hypersonic reentry vehicle subject to
           multiple disturbances
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Yue Yu, Honglun Wang, Na Li, Huiping Zhang, Zikang Su, Xingling Shao In this paper, a scheme which combines finite-time model-assisted active disturbance rejection control and novel greedy criterion-based salp swarm algorithm is developed for attitude tracking problem of hypersonic reentry vehicle with multiple disturbances. To simplify control structure, the control scheme is designed within the framework of active disturbance rejection control completely. To lessen tuning parameters, a sigmoid function-based tracking differentiator is employed to generate a more realizable attitude transient profile instead of utilizing conventional nonlinear tracking differentiator. Taking known model information as model-assisted term, finite-time model-assisted extended state observers are constructed to estimate the lumped disturbance in attitude and angular rate loop with employment of function fal. To achieve rapid response and strong robustness, finite-time model-assisted control laws are derived by utilizing function fhan. Finally, a novel greedy criterion-based salp swarm algorithm is used to optimize control parameters in finite-time model-assisted control laws to achieve optimal solution that minimizes the tracking error and energy consumption. Comparative simulations are conducted to illustrate the effectiveness of the proposed scheme.
       
  • Rotor blade shape reconstruction from strain measurements
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Giovanni Bernardini, Roberto Porcelli, Jacopo Serafini, Pierangelo Masarati Traditional helicopter blades are subject to significant deformations, which influence control forces and moments, as well as the helicopter aeroelastic and aeroacoustic behavior. Thus, the knowledge of rotor elastic states could help improving flight control efficiency, and reducing vibration level and acoustic emissions of next-generation helicopters. This paper presents an original and computationally efficient modal approach aimed at dynamic shape sensing of helicopter rotor blades. It is based on strain measurements in a limited number of points over the blade surface. Although the algorithm is based on the cascaded solution of linear algebraic equations, much like other modal-based algorithms, it is able to reconstruct nonlinear, moderate lag, flap and torsional deflections, which are typical in helicopter structural dynamics. The algorithm is tested on non-rotating and rotating hingeless blades through numerical simulations based upon a multibody dynamics solver for general nonlinear comprehensive aeroelastic analysis. Its capabilities are assessed against those of classical modal approaches. Numerical investigations show that the proposed algorithm is reliable, accurate and robust to measurement noise.
       
  • Parameter estimation for optimal asteroid transfer trajectories using
           supervised machine learning
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Haibin Shang, Xiaoyu Wu, Dong Qiao, Xiangyu Huang In this paper, supervised machine learning is applied to the parameter estimation for optimal asteroid transfer trajectories. Efficient models for the estimation of important trajectory parameters are developed based on the Gaussian Process Regression (GPR) technique. The essence of constructing the GPR-based model is to learn the correlation between the trajectory parameters and the selected features. The asteroid orbital elements are considered as an original feature set due to their decisive influence on transfer trajectories. Two strategies are introduced to enhance the prediction performance of GPR-based models. The first one, the grouping strategy, is able to improve the prediction accuracy by dividing the candidate asteroids into several groups. The second one is that two new compound features are constructed based on the idea of feature extraction, whose function is to provide more crucial information for the inference of transfer time. The efficiency of the proposed models is substantiated by evaluating the global optimal two-impulse transfers to inner main-belt asteroids. This paper provides a basic framework for evaluating the interplanetary trajectories by using supervised machine learning. The proposed approach can be easily extended to solve other trajectory optimization and analysis problems.
       
  • Dynamics of flexible multibody systems with variable-speed control moment
           gyroscopes
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Xiao Feng, Yinghong Jia, Shijie Xu This paper presents a generic global matrix formulation for the dynamics of flexible multibody systems with variable-speed control moment gyroscopes (VSCMGs). The flexible bodies are assumed to exhibit only small deformation, and they are connected in a tree topology by hinges permitting large rotation and translation. A cluster of VSCMGs is mounted on each body for actuation; it is assumed that the VSCMGs are statically and dynamically balanced, and their rotors are axisymmetric. A minimum set of dynamic equations are derived systematically via a mixed use of Kane's method and Newton–Euler equations. The parameters of each flexible body are augmented to take into account the inertias of the attached VSCMGs. Moreover, a skew-symmetric gyroscopic matrix and three control-input-mapping matrices are defined to represent the passive and the active gyroscopic torques of the VSCMGs in a global matrix manner. Three examples are given to show the usefulness, versatility, and correctness of the proposed formulation. As an additional contribution, also presented are linear dynamic equations for a spacecraft with flexible appendages and embedded VSCMGs.
       
  • On maximizing safety in stochastic aircraft trajectory planning with
           uncertain thunderstorm development
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Daniel Hentzen, Maryam Kamgarpour, Manuel Soler, Daniel González-Arribas Dealing with meteorological uncertainty poses a major challenge in air traffic management (ATM). Convective weather (commonly referred to as storms or thunderstorms) in particular represents a significant safety hazard that is responsible for one quarter of weather-related ATM delays in the US. With commercial air traffic on the rise and the risk of potentially critical capacity bottlenecks looming, it is vital that future trajectory planning tools are able to account for meteorological uncertainty. We propose an approach to model the uncertainty inherent to forecasts of convective weather regions using statistical analysis of state-of-the-art forecast data. The developed stochastic storm model is tailored for use in an optimal control algorithm that maximizes the probability of reaching a waypoint while avoiding hazardous storm regions. Both the aircraft and the thunderstorms are modeled stochastically. The performance of the approach is illustrated and validated through simulated case studies based on recent nowcast data and storm observations.
       
  • Optimal reconfigurations between equilibria of two-craft electromagnetic
           formations along manifolds
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Da-wei Qi, Le-ping Yang, Yan-wei Zhu, Yuan-wen Zhang, Yi-peng Li As a novel approach to control the relative motion of a spacecraft formation, electromagnetic formation flight (EMFF) has some prominent advantages, such as no propellant consumption and no plume contamination. The relative motion actuated by inter-craft electromagnetic force/torque is characterized by equilibrium states which could be utilized to accomplish particular missions, such as close formation, interferometer, etc. However, to maneuver among and maintain these equilibrium configurations, the control capability would be insufficient with only electromagnetic actuation and the inertial thrust is required, so an optimal method which exploits the invariant manifold theory is investigated in this paper. Firstly, the nonlinear translational dynamic model of two-craft electromagnetic formations is derived, and then relative equilibrium configurations and their stabilities are analytically studied. Secondly, the manifolds displaying characteristics of equilibria for the unstable equilibrium configurations are analyzed for the first time. Based on these manifolds, a novel and generalized method is proposed to formulate and parameterize optimal reconfigurations from one electromagnetic equilibrium configuration to another with the electromagnetic control inputs from the initial value to the target value. Specifically, the system's uncontrolled and discontinuous flows along manifolds compose majority of the transfer trajectories, and then optimal controls are applied to a portion of the discontinuous trajectories to differentially correct them to match continuity. By defining the control histories as a finite set of time independent variables, the optimal control problem is converted to a parameter optimization problem and solved by Particle Swarm Optimization. The method can attain the shape-changing ability and consume as little inertial thrust as possible, in exchange for added electromagnetic control effort. Lastly, numerical simulations are presented to verify the feasibility and optimality of the designed method.
       
  • Automatic Carrier Landing System multilayer parameter design based on
           Cauchy Mutation Pigeon-Inspired Optimization
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Zhiyuan Yang, Haibin Duan, Yanming Fan, Yimin Deng The parameter adjusting in Automatic Carrier Landing System (ACLS) is a time-consuming and tedious task. In order to improve the efficiency of the adjusting task and overcome the difficulties in the manual parameter adjustment, a multilayer optimization strategy, in which ACLS is clearly divided into four layers including inner loop, autopilot, guidance control and guidance compensation, is proposed in this study and adopted for the parameter design. Besides, a novel algorithm, named Cauchy Mutation Pigeon-Inspired Optimization (CMPIO) which is inspired by Cauchy distribution, is proposed to optimize ACLS parameters in each layer. Comparative simulations are conducted to verify the feasibility of the multilayer design strategy and the superiority of CMPIO. To enhance the authenticity of the simulations in the guidance compensation layer, some stochastic conditions are considered with different deck motion, air wake and radar noise turbulences alleviated by several rejection methods. The simulation results prove that the designed ACLS based on the multilayer design strategy satisfies the acknowledged criteria including the time and the frequency domain. Furthermore, the stability of the inner loop and the autopilot integrated with Approach Power Compensation System (APCS) are confirmed.
       
  • Analysis and experiment of a bio-inspired flyable micro flapping wing
           rotor
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): S. Guo, H. Li, C. Zhou, Y.L. Zhang, Y. He, J.H. Wu Inspired by insect flapping wings, a novel flapping wing rotor (FWR) has been developed for micro aerial vehicle (MAV) application. The FWR combines flapping with rotary kinematics of motions to achieve high agility and efficiency of flight. To demonstrate the feasibility of FWR flight and its potential MAV application, an extensive and comprehensive study has been performed. The study includes design, analysis, manufacture, experimental and flight test of a flyable micro FWR model of only 2.6 g weight. By experiment, the FWR kinematic motion and aerodynamic lift were measured using high speed camera and load cells. Within a range of input power, the difference between the measured aerodynamic force and the analytical results by a quasi-steady model was found to be within 3.1%–15.7%. It is noted that the FWR aeroelastic effect plays a significant role to obtain an ideal large angle of attack especially in up-stroke and enhance the FWR performance. Further analysis of the unsteady aerodynamic characteristics has been carried out based on the detailed airflow field of the FWR in a flapping cycle by CFD method. A successful vertical take-off and short hovering flight of the micro FWR model has been achieved for the first time in the research field. The flight test demonstrates the FWR feasibility and its unique feature of flight dynamics and stability for the first time. These characteristics have also been simulated by using ADAMS software interfaced with the aerodynamic model.
       
  • Generalized error analysis of analytical coarse alignment formulations for
           stationary SINS
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Felipe O. Silva This communication presents additional results on a recently published work of the author [1], which addressed the stationary coarse alignment (CA) stage of strapdown inertial navigation systems (SINS). As main contribution of this communication, the error analysis proposed in [1] is extended, and novel general expressions for the SINS CA errors are derived, which are valid regardless of the inertial measurement unit (IMU) orientation, and present hence, greater practical applicability. The general error expressions prove to be similar to the simplified equations derived in [1], but with body frame coordinates replaced by navigation frame coordinates. Simulation results validates the adequacy of the outlined verifications, and are in agreement with experimental results found in the literature.
       
  • Mean flow compressibility effects in transonic turbulence modeling
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Jinglei Xu, Dashuai Chen, Youfu Song, Shengcheng Ji, Yu Zhou The mean flow compressibility effects greatly influence the behavior of turbulent flows, as long as the flow is compressible. The fact is even though Favre average has taken into account the variation of the density, less accurate CFD results are always obtained when the flow is compressible. Thus, many compressibility corrections are made for high Mach number flows. As for the transonic turbulence flow, the mean flow compressibility effects are not mentioned. In this paper, it is demonstrated that the mean flow compressibility effects are not ignorable in transonic flows on some flow features. The mean flow compressibility effects are taken into account by introducing a characteristic turbulence length scale. The key is a new definition of vorticity by the curl of momentum. A compressible von Kármán length scale is introduced to obtain a new turbulence model CKDO (Compressible Kinetic Dependent Only) for complex compressible flows on the basis of the KDO. The only two empirical coefficients in the KDO model are not changed, which were calibrated by a slice of the incompressible flat plate boundary layer flow. Numerical simulations of transonic flows around RAE2822 airfoil, axisymmetric bump pipe and ONERA-M6 wing show that compressibility is non-negligible, and the new length scale definition can improve the prediction accuracies of aerodynamic features, such as the onset locations of shock waves, skin friction and pressure coefficients.
       
  • Computational investigations of water collection efficiency on blades in
           unsteady vortex flowfield of rotor
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Xi Chen, Qi-Jun Zhao To predict ice accretion on the helicopter rotor more accurately, a three-dimensional Eulerian method with a shadow zone dispersion model is developed for calculating the water collection efficiency on blades in the unsteady vortex flowfield of the rotor. Firstly, the unsteady vortex flowfield of the rotor is calculated using a CLORNS code. Secondly, considering the 3-D effect of the rotor deeply, the droplet flowfield on the same embedded grids is solved by the Eulerian method to overcome the defects of traditional 2-D calculation methods for predicting rotor icing. To increase the stability and efficiency of the Eulerian method, the shadow zone dispersion model is presented. Thirdly, the calculated results are respectively validated through the ice amount comparisons with experimental results of UH-1H rotor and SRB rotor. The simulated results show that the blade-tip vortex has a significant effect on the water collection efficiency and causes a drop in the water collection amount along the blade spanwise direction. Finally, the effects of the advance ratio and the forward tilting angle of the rotor shaft on the water collection efficiency are calculated and analyzed, and some new conclusions are obtained. In forward flight, the blade-tip vortex has a more obvious effect on the water collection efficiency in the advancing blade than that in the retreating blade, and this effect decreases with the increase of the advance ratio and the forward tilting angle.
       
  • Wing flexibility effects on the flight performance of an insect-like
           flapping-wing micro-air vehicle
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Anh Tuan Nguyen, Jae-Hung Han This study explores the effects of wing flexibility on several characteristics of flight, in this case the trim conditions, power requirements and dynamic stability of an insect-like flapping-wing micro-air vehicle (FWMAV) based on the hawkmoth Manduca sexta. The wing structure is analyzed by the finite-element method. A potential-based aerodynamic model which encompasses the unsteady panel method and the extended unsteady vortex-lattice method is employed to compute the aerodynamic forces. The motions of the FWMAV are obtained using a flexible multibody dynamics program coupled with the potential-based aerodynamic model. The results of this study show that the trim conditions of insect-like flexible and rigid FWMAVs may differ significantly from each other. When the flight speed is less than 3.0 m/s, using flexible wings is favorable, as they help the FWMAV reduce the power requirement and stabilize the lateral dynamics. However, at 3.0 m/s, these advantages are almost unnoticeable, while at 4.0 m/s, the flexible insect-like FWMAV requires even more mechanical power than its rigid counterpart.
       
  • Feasible zone for planetary entry vehicles
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Zixuan Liang, Jian Chen, Zhang Ren Understanding the coverage of ground track is conducive to evaluating an entry vehicle's maneuver capability, especially for an entry mission with waypoint constraint. This paper investigates a feasible zone which describes the lateral corridor of the entry vehicle's ground track. Any point inside the feasible zone is supposed to be reachable from the initial condition and controllable to the terminal condition. Analyses show that the zone boundary consists of two or three phases. For each phase, the zone boundary is generated by solving one or more trajectory optimization problems. The feasible zone can be employed to judge whether or not a waypoint is feasible to the vehicle. Moreover, to evaluate the feasible level of the waypoint, an evolved feasible zone with pass index is defined and calculated. The feasible zone is simulated for an Earth entry vehicle in various missions. Dispersions are considered in the simulation to analyze the influence of aerodynamic uncertainties.
       
  • Study on pyroshock propagation through plates with joints and washers
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Juho Lee, Dae-Hyun Hwang, Jae-Hung Han Pyrotechnic release devices are widely used in various missions in order to reliably separate the structural parts of the system. However, the pyroshock induced by an explosive pyrotechnic event can lead to fatal malfunctions of the adjacent electrical components. In order to mitigate these pyroshock issues, an accurate understanding of the pyroshock propagation in structures is essential. In this study, an experimental setup for the pyroshock propagation experiments is developed with the pyroshock excitation using pyrotechnic initiators. The pyroshock propagation analysis environment with a commercial hydrocode is established and verified through comparison between the analysis and the experimental results. The pyroshock propagates through the thin plates in the form of flexural waves (or anti-symmetric Lamb waves). Using the established numerical and experimental techniques, the effects of the pyroshock attenuation by the joints and washers are investigated. The plates connected by joints with different materials and the plates connected by joints with inserted washers made of different materials and in different thickness are considered. The experimental and numerical results are in good agreement: the pyroshock attenuation is highly effective when the joints are made of higher density and stiffness materials and when the thickness of the washers is increased. The primary reason for the pyroshock attenuation due to the joints and washers is the flexural wave reflection at the discontinuities caused by acoustic impedance mismatching.
       
  • Cooperative guidance with multiple constraints using convex optimization
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Huan Jiang, Ze An, Ya'nan Yu, Shishi Chen, FenFen Xiong In the existing closed-loop cooperative guidance approaches for salvo attack of multiple missiles, the multiple constraints and time-variant velocity basically cannot be effectively considered. Therefore, two closed-loop cooperative guidance methods are developed in this paper, by employing the efficient convex optimization technique and receding horizon control (RHC) strategy. During each guidance cycle of RHC, the system coordination target is updated and then broadcasted to each missile as a constraint. Subsequently, the convex optimization technique is utilized to solve the multi-constraint optimal proportional guidance problem of each missile online to achieve the consensus on time-to-go among missiles. Simulation results show that for three cases with different conditions of velocity, the cooperative simultaneous attack under multiple constraints can be effectively carried out using each of the two proposed cooperative guidance laws, which verify their effectiveness and feasibility.
       
  • Roll reversal phenomenon control in flight vehicles
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Mojtaba Mirzaei Roll reversal is one of the most important and challenging phenomena that takes place in some flight vehicles including canard control vehicles. When the roll reversal phenomenon occurs the vehicle rotates in the reverse direction of the roll command. In this situation, the control system will be improper unless this phenomenon can be predicted and accounted for in advance. In this paper, various methods that are used in flight vehicles to mitigate this phenomenon are described. Then, a new control method is developed by using only rate gyro and fin deflection feedback without changing the vehicle aerodynamic configuration. In the proposed method, the negative effect of roll reversal phenomenon is eliminated by using sliding mode control as a robust method taking into account the uncertainty involved in the subject. This control method is on the basis of an online identifier that estimates the roll effectiveness sign and consequently determines the direction of controller command. Finally, this method has been implemented in a six DOF flight simulation that resulted in desirable roll performance in various flight states and therefore verifies the proper performance of this new control method.
       
  • Multi-fidelity aerodynamic design trade-off exploration using
           point-by-point Pareto set identification
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Anand Amrit, Leifur Leifsson, Slawomir Koziel Aerodynamic design is inherently a multi-objective optimization (MOO) problem. Determining the best possible trade-offs between conflicting aerodynamic objectives can be computationally challenging when carried out directly at the level of high-fidelity computational fluid dynamics simulations. This paper presents a computationally cheap methodology for exploration of aerodynamic design trade-offs. In particular, point-by-point identification of a set of Pareto-optimal designs is executed starting in the neighborhood of a single-objective optimal design, and using a trust-region-based, multi-fidelity optimization algorithm as well as locally constructed response surface approximations (RSAs). In this work, the RSAs are constructed using second-order polynomials without mixed terms, multi-fidelity models, and adaptive corrections. The application of the point-by-point MOO algorithm is demonstrated through MOO of transonic airfoil shapes using the Reynold–Averaged Navier Stokes equations and the Spalart–Allmaras turbulence model. The results demonstrate that the Pareto front in the neighborhood of an initial design can be obtained at a low cost when considering up to 12 design variables. The results also indicate that the computational cost of the optimization process grows slowly with the number of the design variables, and the repeatability of the algorithm is very good when starting the search from different initial points.
       
  • Nonlinear response and buckling analysis of eccentrically stiffened FGM
           toroidal shell segments in thermal environment
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Pham Minh Vuong, Nguyen Dinh Duc This paper presents an analytical approach to study nonlinear response and buckling analysis of FGM toroidal shell segments reinforced by FGM stiffeners surrounded by elastic foundations in thermal environment and under external pressure. The formulations are based on Reddy's third-order shear deformation shell theory (TSDT) with von Karman nonlinearity, Pasternak type elastic foundations and smeared stiffener technique. By applying Galerkin's method and using stress function, closed-form expressions for determining the static critical external pressure load and postbuckling load–deflection curves are determined. Finally, the influences of geometrical parameters, volume fraction index, elastic foundations, and the effectiveness of stiffeners on the stability of shells are considered.
       
  • Weakly nonlinear instability of viscoelastic planar sheets with initial
           varicose disturbances
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Luo Xie, Li-Jun Yang, Jun-jie Wang, Li-zi Qin Viscoelastic sheets, moving in an inviscid gas with initial varicose disturbances, have been investigated by performing a second-order temporal weakly nonlinear instability analysis based on the perturbation technique. The Oldroyd-B equation is considered as the rheological model of viscoelastic fluid. The solutions of the second-order disturbances have been derived, including the second-order dispersion relation and the corresponding interface displacement. The results showed that the second-order interface displacement of the varicose mode was also varicose, which interacts with the fundamental varicose wave, causing disintegration of sheets at full-wavelength intervals and resulting in ligaments consisting of two connected swells. Much smaller satellite ligaments were also formed soon after breakup within such ligaments. Different breakup behaviors and mechanisms between sheets with initial varicose and sinuous disturbances are displayed and analyzed. It is found that the eventual shape of sheets depends mainly on three factors, the first-order and second-order temporal growth rates and the second-order disturbance amplitude. The breakup time has been calculated to assess the extent of nonlinear instability. The influence of dimensionless rheological parameters on instability, i.e. elasticity number and time constant ratio, are examined via comparison of the three key factors, breakup time and wave deformation at the shortest breakup time.
       
  • A new efficient simulation method based on Bayes' theorem and importance
           sampling Markov chain simulation to estimate the failure-probability-based
           global sensitivity measure
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Yanping Wang, Sinan Xiao, Zhenzhou Lu The failure-probability-based global sensitivity measure can detect the effect of input variables on the structural failure probability, which can provide useful information in reliability-based design. In this paper, a new efficient simulation method is proposed to estimate the failure-probability-based global sensitivity measure. The proposed method is based on the Bayes' theorem and importance sampling Markov chain simulation. The Bayes' theorem is used to provide a single-loop simulation method and the importance sampling Markov chain simulation is used to further reduce the computational cost. Compared to the traditional double-loop Monte Carlo simulation method, the proposed method requires only a single set of samples to estimate the failure-probability-based global sensitivity measure and its computational cost does not depend on the dimensionality of input variables. Finally, one numerical example and two engineering examples are presented to illustrate the accuracy and efficiency of the proposed method.
       
  • Non-cooperative maneuvering spacecraft tracking via a variable structure
           estimator
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Zhai Guang, Bi Xingzi, Zhao Hanyu, Liang Bin A spacecraft performing unknown maneuvers significantly increases the probability of a collision between spacecraft with neighboring orbits. Traditional orbit determination filters cannot robustly cope with unknown maneuvers. To track non-cooperative, unknowingly maneuvering spacecraft, a novel variable structure estimator is proposed based on the input compensation to a normal filter. We develop an observer to estimate the unknown maneuver and then analyze the estimated maneuver performance based on error propagation. Once the maneuver detector declares the occurrence of an unknown maneuver, the estimated maneuver is fed to an extended Kalman filter as compensation, which enables the estimator to work adaptively. Finally, a series of numerical simulations are carried out to demonstrate the effectiveness of the proposed variable structure estimator, and the estimation performances in the cases of constant and time-varying maneuvers are analyzed based on the simulation results.
       
  • Comparison of box-wing and conventional aircraft mission performance using
           multidisciplinary analysis and optimization
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Stephen A. Andrews, Ruben E. Perez Box-wing aircraft designs have the potential to achieve significant reductions in fuel consumption. Closed non-planar wing designs have been shown to reduce induced drag and the statically indeterminate wing structure can lead to reduced wing weight. In addition, the streamwise separation of the two main wings can provide the moments necessary for static stability and control, eliminating the weight and aerodynamic drag of a horizontal tail.Proper assessment of the disciplinary interactions in box-wing designs is essential to determine any realistic performance benefits arising from the use of such a configuration. This study analyzes both box-wing and conventional aircraft designed for representative regional-jet missions. A preliminary parametric investigation shows a lift-to-drag ratio advantage for box-wing designs, while a more detailed multidisciplinary study indicates that the requirement to carry the mission fuel in the wings leads to an increase of between 5% and 1% in total fuel burn compared to conventional designs. However, the multidisciplinary study identified operating conditions where the box-wing can have superior performance to conventional aircraft despite the fuel volume constraint.
       
  • High blade lift generation through short rotor–stator axial spacing
           in a tiny pump
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Han Xu, Donghai Jin, Mengyu Wang, Lin Du, Dakun Sun, Xingmin Gui, Xiaofeng Sun Short rotor–stator axial spacing has been demonstrated to be beneficial to the aerodynamic performance of subsonic compressors. In this paper, it is further verified that this benefit partly originates from the improvement of the rotor blade lift. A tiny axial pump is investigated both numerically and experimentally with three different rotor–stator axial spacings. The time-accurate simulation indicates that both the peak and average rotor blade lifts are enhanced as the axial spacing decreases. The potential field of the downstream stator has significant effects on the pressure distribution in the rotor when the blade rows get close. The two-dimensional (2D) PIV measurement demonstrated that short axial spacing generates high circulation around the rotor blade due to the flow tube compression, which contributes to the blade lift improvement. Besides, close blade-rows axial spacing generates enhanced unsteadiness for the inlet flows of the downstream stator, which should be taken into consideration in the design process.
       
  • The influences of the header geometry on hydrocarbon fuel flow
           distribution in compact parallel channels
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Yuguang Jiang, Jiang Qin, Yaxing Xu, Silong Zhang, Khaled Chetehouna, Nicolas Gascoin, Wen Bao Parallel cooling channels have been a commonly seen configuration in advanced aero-engines, for example, the scramjet. However, the mal-distribution of hydrocarbon fuel in cooling channels may cause waste of fuel cooling capacity and even over-temperature of the engine structure. In order to ensure the cooling effect and the structure safety, the header geometry should be designed carefully. In this work, the parametric analysis of the header geometries was carried out under the limitations of compact geometry and high temperature environment in scramjet cooling channels. A 3D numerical model of the hydrocarbon fuel flow and heat transfer under supercritical pressure in parallel channels was developed. The flow area ratio of the inlet and outlet headers, feeding tube and header aspect ratio were selected as the main parameters of the parametric analysis. The results indicate that proper design of the headers could improve the uniformity of flow distribution and cooling effects obviously. Local optimums of flow area of the inlet/outlet headers and header aspect ratio exist. The outlet header should be larger which contains the heated fuel. Proper feeding tube improves the flow distribution by the injection effect in the header. The header aspect ratio performs better when the wet perimeter is smaller. The results offer possible advice for the header design limited by compact size and high temperature environment.
       
  • A numerical method for the solution of supersonic streamwise vortex
           dynamics
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Davide Viganò, Luca Maddalena In this work a numerical model for the solution of supersonic streamwise vortices is presented. It is known that the canonical solution of the supersonic horseshoe line-vortex collapses to the counterpart subsonic Biot–Savart solution in a region of the domain that is both function of the radial distance from the source as well as the extension of the cone of influence at the specific downstream location. It is proposed in here to separate the flow in two regions: a near field where techniques that have been developed for the treatment of the singularity in subsonic point vortex methods can be employed, and a far field solution of the supersonic vortex source that retains the hyperbolic nature of the problem. The definition of the extent of the respective domains, as well as the conditions for a congruent transition are the subjects of this investigation. A polynomial approximation for the determination of the transition location is derived. A comparison between simulations utilizing the proposed model and measurements from a series of experiments conducted in a Mach 2.5 flow is discussed.
       
  • A study on adaptive vibration control and energy conversion of highly
           flexible multifunctional wings
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Natsuki Tsushima, Weihua Su In this paper, a highly flexible multifunctional wing with embedded piezoelectric materials and thin-film battery cells for adaptive vibration control and energy harvesting is studied. It provides a description of the electro-aeroelastic equations of multifunctional wings with piezoelectric devices functioning as both actuators for active vibration control and energy harvesters. The energy harvesters also act as dampers for passive vibration control. An LQR controller is implemented for the feedback control of the piezoelectric actuators. The optimal selection of the pre-placed piezoelectric device configuration for efficient flutter suppression is explored by minimizing the state and control costs while maximizing the harvesting output. The priority of the multifunctional wing design is put on a capability of vibration alleviation than energy harvesting. In addition, an active control algorithm for gust alleviation adaptively switching piezoelectric device functions is developed. A multifunctional wing that takes advantage of both active actuation and energy harvesting is then numerically studied by exploring the state, control, and harvesting costs in different numerical simulations under gust disturbances and aeroelastic instabilities. Finally, an energy storage design using thin-film lithium-ion batteries is considered to accumulate the harvested energy from piezoelectric devices. The performance of the multifunctional wing with such energy storage device is also explored.
       
  • Modeling and dynamics of a bare tape-shaped tethered satellite system
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): B.S. Yu, P.B. Dai, D.P. Jin This paper focuses on the rigid-flexible coupling modeling and dynamics of a bare tape-shaped Tethered Satellite System (TSS). The rigid element is adopted to discretize the tape-shaped tether into a system of rigid bodies with equivalent linear springs and dampers serving as the junctions between the adjacent rigid elements. The equations of motion of the rigid elements are obtained using Newton's second law and the theory of angular momentum. Further, the influence of environmental perturbations on the dynamics of the tape-shaped TSS is investigated, including the atmospheric drag, electrodynamic force, and heating impact. The simulation results show that complicated dynamic phenomena for attitude motions and tether configuration changes will be observed in the tape-shaped bare tethered satellite system.
       
  • Elastic buckling and free vibration analyses of porous-cellular plates
           with uniform and non-uniform porosity distributions
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Pham Toan Thang, T. Nguyen-Thoi, Dongkyu Lee, Joowon Kang, Jaehong Lee The aim of this research paper is to present the elastic buckling and free vibration analyses of porous-cellular plates based on the first-order shear deformation theory (FSDT). In the porous-cellular plate model, porosities are dispersed by uniform and non-uniform (symmetric and asymmetric) distribution patterns. The material properties, such as Young's modulus and mass density of the porous-cellular plates are assumed to vary along the thickness direction in term of porosity coefficient. First, the dynamic version of Hamilton's principle is applied to derive the Euler–Lagrange equations. Then, in the case of simply supported boundary condition, the critical buckling load and natural frequency of the porous-cellular plates are obtained using the Navier procedure. Furthermore, the reliability of the current formulation is validated by several examples. Finally, a comprehensive examination into the influence of porosity coefficient, porosity distributions, and the geometric parameters on the buckling behavior and vibration response of the porous-cellular plates are performed. Numerical results indicate that the effect of porosity distributions on the structural performance and provide the useful insights into the porosity design to achieve appropriately natural frequency and buckling resistance.
       
  • Modelling strategies for the prediction of hot streak generation in lean
           burn aeroengine combustors
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Antonio Andreini, Tommaso Bacci, Massimiliano Insinna, Lorenzo Mazzei, Simone Salvadori The accurate prediction of the fluid dynamic conditions at the exit of gas turbine combustors are of paramount importance in the aero-thermal design of the aero-engine. In fact, both the heat loads and the aerodynamic performance of the high pressure turbine (HPT) are substantially affected by the entry conditions, such as velocity components, temperature and turbulence intensity.The problem is particularly serious in new generation devices based on a lean burn concept. Compared to standard Rich–Quench–Lean (RQL) scheme, the absence of dilution jets and the use of highly swirled flows for flame stabilization make the control of combustor exit temperature distribution a complex task. Therefore, the high-fidelity prediction of the hot streak formation within the combustor, as well as its propagation through the HPT, are becoming key aspects.In this work, different strategies for turbulence modelling are tested, mainly focusing on scale-resolving approaches such as Large-Eddy Simulation (LES) and Scale Adaptive Simulations (SAS), which are becoming increasingly popular with the availability of more powerful computational resources. At the same time, classical eddy-viscosity models based on RANS approach are considered, as they still represent the standard simulation strategy in the industrial framework, when a fast response is required in a preliminary design phase.The different methodologies are benchmarked on an experimental test article representative of an aeronautical lean burn combustor cooled by means of effusion. The benchmark performed at engine-relevant conditions allowed to draw interesting conclusions for the purposes of the aero-thermal simulation. SAS proved to be a valid alternative to LES, returning on the whole the same level of accuracy. As expected, the disagreement obtained with RANS was significant. The sensitivity to the turbulent Prandtl number was investigated to provide an insight on its reliability in compensating the underestimation in turbulence mixing.
       
  • Optimum distributed wing shaping and control loads for highly flexible
           aircraft
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Jared R. Hammerton, Weihua Su, Guoming Zhu, Sean Shan-Min Swei In highly flexible aircraft, the large structural slenderness associated to their high-aspect-ratio wings, while bringing challenges to the design, analysis, and control of such aircraft, can be pro-actively exploited for improving their flight performance, resulting in mission-adaptive morphing configurations. This paper studies the optimum wing bending and torsion deformation of highly flexible aircraft, with distributed control loads along the wing span to achieve the optimum wing geometry. With the goal of improving flight performance across the entire flight regime, a modal based wing shaping optimization is carried out, subject to the requirement of trim and control cost limitation. While a single objective of the minimum drag can be used to find the optimum wing geometry, this paper further considers a trade-off between flight efficiency and structural integrity. In this trade-off study, a multi-objective optimization is formulated and performed, targeting for both minimizing the drag to improve flight efficiency and reducing the gust-induced wing bending moment to enhance the structural integrity. Finally, this paper explores the minimum control cost for different targets of combined flight efficiency and structural integrity. This paper provides not only an efficient way to search for the desired wing planform geometry at a given flight condition but also insights of the required control effort that is necessary to maintain the wing geometry.
       
  • Finite-time H ∞ adaptive attitude fault-tolerant control for reentry
           vehicle involving control delay
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Mingzhou Gao, Jianyong Yao This paper proposes a finite-time adaptive fault tolerant control method for the attitude control of reentry vehicle, by combining the radial basis function (RBF) network technology with adaptive fault tolerant control method. We simultaneously considered actuator faults, control delay, input saturation, time-varying parameter uncertainties and external disturbances when designing the control method. The theoretical part of this paper includes the establishment of attitude dynamic model concerning actuator faults and the design of finite-time H∞ adaptive attitude fault-tolerant controller. We proved the stability of our proposed adaptive attitude fault-tolerant controller through the Lyapunov function and the linear matrix inequality (LMI) method. The simulation results show that our proposed method not only can effectively deal with actuator faults in the attitude control system, but also has very good robustness for control delay, input saturation, time-varying parameter uncertainties and external disturbances.
       
  • Integrated robust adaptive tracking control of non-cooperative fly-around
           mission subject to input saturation and full state constraints
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Yi Huang, Yingmin Jia This paper investigates the relative position and attitude tracking control of non-cooperative fly-around mission in the presence of parameter uncertainties, external disturbances, input saturation and full state constraints. Firstly, an integrated and coupled 6 DOF relative motion dynamic model is established, which is consisted of relative position model depicted in the line-of-sight (LOS) frame and relative attitude model described by Modified Rodriguez parameters (MRPs). Subsequently, by using the backstepping control method, an integrated robust adaptive anti-windup control scheme is proposed, in which uncertain parameters and unknown upper bound of the disturbances are estimated by adaptive technique, and the adverse effects caused by input saturation are reduced by the designed anti-windup compensator. To guarantee the full state constraints satisfied all the time, the barrier Lyapunov function method is incorporated into the backstepping control design. Rigorous stability proofs show that the designed robust adaptive controller guarantees that the relative motion states not only can be restricted in the prescribed constraint regions, but also can converge into the small regions with good robustness. Finally, numerical simulation results demonstrate the effectiveness and performance of the designed control scheme.
       
  • Adaptive collision-free formation control for under-actuated spacecraft
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Xiaoping Liu, Ziyang Meng, Zheng You This paper proposes an adaptive collision-free formation control strategy for a team of under-actuated spacecraft subject to parametric uncertainties. The objective is to drive follower spacecraft to form a prescribed shape around a leader, while collision avoidance is achieved among different spacecraft. To explore the under-actuated nature of the studied spacecraft, a hierarchical inner-outer loop strategy is adopted. First, in the outer position loop, a virtual force is synthesized by introducing negative gradients of novel potential functions with respect to the distances between spacecraft such that the collision-free formation objective is completed. Based on the synthesized virtual force, an applied thrust and a command attitude are extracted. Then, in the inner attitude loop, an applied torque is designed for each individual spacecraft to track the command attitude. Moreover, during the virtual force and applied torque syntheses, adaptive laws are developed to estimate and compensate the uncertain inertial parameters. In terms of Lyapunov theory, it is shown that the spacecraft trajectories driven by the proposed controller ultimately converges to a neighborhood of the desired formation. Finally, illustrative simulations are performed to verify the proposed theoretical results.
       
  • Numerical investigation on the assistant restarting method of variable
           geometry for high Mach number inlet
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Yuan Liu, Lu Wang, Zhansen Qian To compromise the compression efficiency and the starting properties, the inner contraction ratio (ICR) of a general high Mach number inlet is usually designed in the range of dual solution area. When going into an unstarted status, the high Mach inlet needs an assistant method to restart. This work explores a variable geometry method to restart the inlet. The rotating cowl is adopted to a typical Mach 4 cruising inlet, and the unsteady computation method with a dynamic Chimera grid technique is applied to simulate the rotating process of the inlet cowl. The change characteristics of the restarted performance at different rotating angle amplitude of the inlet cowl are investigated systematically. The numerical results reveal that the unstarted status of this typical inlet induced by the effect of high backpressure failed to restart if the inlet cowl rotating angle amplitude is under a small critical value, which is called lower critical angle. The inlet could restart if the cowl rotating angle amplitude is a little larger than the lower critical angle, and the flow may rapidly go to a steady condition after the inlet cowl returns to the design position. However, the performance of the restarted inlet is still worse than the design condition, because of the existence of an stable separation bubble on its shoulder, even if the inlet cowl stops rotating. The separation bubble becomes shrunk with an increasing the cowl rotating angle amplitude. When the inlet cowl rotating angle amplitude reaches a large critical value which is called upper critical angle, the separation bubble disappears, and all the separation is swallowed by the mean flow. Therefore the design performance of the inlet can be recovered, which means that the flow mass capture coefficient, total pressure recovery coefficient, drag and the outlet Mach number go back to the design level. It also shows that within the range of the lower and upper critical angles, the larger the rotating angle amplitude is, the more rapidly the separation bubble reaches stable state.
       
  • Optimization of SD7003 airfoil performance using TBL and CBL at low
           Reynolds numbers
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Dj. Kamari, M. Tadjfar, A. Madadi Both blowing and suction crossing the boundary layer have been widely implemented on the airfoils top surface to control the flow field. These techniques have significant effects on the aerodynamic characteristics of the airfoil. Both methods were applied to Selig–Donovan 7003 (SD7003) airfoil at Reynolds number of 60,000. An optimization technique was used to find the optimum parameters of blowing/suction using genetic algorithm (GA). Considering that computational fluid dynamics CFD is time-consuming for determination of the objective function, an artificial neural network was coupled with GA in order to achieve this aim. We used aerodynamic performance, defined as lift to drag ratio (L/D), as the objective function to find the optimal configuration. Results showed that application of active flow control methods caused a reduction in flow separation zone which resulted in improvement of aerodynamic coefficients. Moreover, it was found that suction was more effective than blowing as a control mechanism.
       
  • Forced vibration analysis of the hard-coating blisk considering the
           strain-dependent manner of the hard-coating damper
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Feng Gao, Wei Sun, Junnan Gao This paper focuses on the passive vibration reduction of the blisk by the hard-coating damper, and investigates the nonlinear dynamics of the hard-coating blisk. Based on the discrete values obtained by the testing, the high-order polynomials are used to characterize the mechanical parameters of the hard-coating damper considering its strain-dependent manner. The boundary conditions and continuity conditions of the disk and the hard-coating blades are satisfied by introducing the artificial springs at their interface. The dynamic model of the hard-coating blisk is constructed by an analytical energy-based approach. An iterative solution procedure based on the Newton–Raphson method is developed to obtain dynamic characteristics of the hard-coating blisk. An academic blisk deposited NiCoCrAlY + YSZ hard coating is selected as the benchmark case to conduct the nonlinear numerical calculation, and the obtained results are compared with those obtained by the experimental test. In particular, the specific influence of the hard-coating damper and the unique strain-dependent manner on the vibration characteristics of the blisk are investigated respectively in terms of the resonant frequencies and corresponding responses.
       
  • Onboard mission allocation for multi-satellite system in limited
           communication environment
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Zixuan Zheng, Jian Guo, Eberhard Gill The purpose of this paper is to seek the suitable local objectives for each satellite to optimal the global mission allocation strategy with a global utility function. This paper uses a game-theoretical formulation for a multi-satellite system in which the satellites are viewed as a unique unit with their self-interests. To solve the problem, the first is to identify the utility functions for individual satellite, align them to form the global utility function which can represents the allocation requirements. The second is to design the suitable negotiation mechanisms that can be equipped on each satellite so they can pursue the optimization by their own interest. The Utility-based Regret play, the Smoke Signal play, and the Broadcast-based play are proposed as negotiation mechanisms for the team to cooperate under the distributed and decentralized system structure. The simulation results illustrate that using these mechanisms can help this multi-satellite system reaches a near-optimal allocation profile. The effectiveness of proposed mechanisms are demonstrated by comparing their simulation results with several existing mechanisms under different scale of participant number.
       
  • Influence of high fidelity structural models on the predicted mass of
           aircraft wing using design optimization
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Odeh Dababneh, Timoleon Kipouros This paper explores the necessary and appropriate level of detail that is required to describe the structural geometry of aircraft wings accurately enough to predict the mass of the main load-carrying wing structure to an acceptable level of accuracy. Four different models of increasing structural fidelity are used to describe the wingbox structure of a realistic real-world aircraft wing. The wingbox of the NASA Common Research Model served as a test model for exploring and analyzing the trade-off between the granularity level of the wingbox geometry description under consideration and the computational resources necessary to achieve the required degree of accuracy. The mass of metallic and composite wingbox configurations was calculated via finite element analysis and design optimization techniques. The results provided an insight into the competence of certain wingbox models in predicting the mass of the metallic and composite primary wing structures to an acceptable level of accuracy, and in demonstrating the relative merits of the wingbox structural complexity and the computational time and input efforts for achieving the required level of accuracy.
       
  • Disturbance observer based control for spacecraft proximity operations
           with path constraint
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Qi Li, Jianping Yuan, Bo Zhang, Huan Wang This paper investigates the application of a nonlinear feedback control strategy for driving a chaser spacecraft to rendezvous and dock with a target spacecraft in space. The nonlinear coupled models are established to describe the relative position and relative attitude dynamics, while a nonlinear disturbance observer is employed to estimate and compensate the external disturbances. Furthermore, a specific potential function is designed to prevent the chaser from entering into the forbidden zone or colliding with the target during the final phase of rendezvous and docking. Within the Lyapunov framework, the ultimate boundedness of the closed-loop system is guaranteed in the existence of external disturbances. Numerical simulations are performed to illustrate the feasibility and effectiveness of the proposed control strategy for motion synchronization as well as collision avoidance.
       
  • Experimental investigation on gliding arc discharge plasma ignition and
           flame stabilization in scramjet combustor
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Rong Feng, Jun Li, Yun Wu, Jiajian Zhu, Xiliang Song, Xipeng Li Ignition and flame stability in supersonic flow have always been the key problems of research in scramjet. In addition, ignition is difficult and the cavity flameholder is susceptible to support the flame stability under extreme conditions such as low equivalent ratio. In recent years, gliding arc plasma is recognized to expand ignition and extinction limit with lower energy consumption in the field of plasma assisted ignition due to its heating and chemical effects. In this paper, a gliding arc igniter has been designed and compared with the traditional spark plug in order to quantify the ignition ability. The igniter has the same size with the spark plug, using low-power AC gliding arc to carry out ethylene ignition test in Ma = 2.52 Ma supersonic flow. The average power of gliding arc discharge is 1199 W. A high-speed camera and CH⁎ chemiluminescence were used to make combustion diagnosis. Founded in the same discharge period, the lean ignition limit of the gliding arc is lower than the ignition limit of the spark. The average expansion of ethylene ignition limit is 17%. The ignition process is that gliding arc continues to generate the initial flame kernels during the discharge period, but it is extinguished continuously due to the strong convection. Until generating an initial flame kernel which can successfully propagate the flame. The ignition process can be divided into four stages. It continues to generate new flame kernels in flame propagation process. Gliding arc reignites the fuel and generates the new flame kernels after forming a stable flame, appearing intermittent ignition in the cavity. The high equivalent ratio can make ignition delay time shorter, generating initial flame kernels more frequently. The heating effect of the gliding arc and reignition character make the thermal product and ethylene occur intermittent combustion more often in the cavity, increasing the area of the combustion reaction. Gliding arc plasma can achieve combustion enhancement during the flame stabilization process. The shear layer of flame thickness increased by the average of 2 mm on S-B-1 and G-B-1 conditions. Compared with the traditional spark ignition, gliding arc broaden the lean blow-off limit in different stages may be the significant reason for broadening lean ignition limit. It concludes that gliding arc makes the flame's ignition limit closer to the flame's blow-off limit.
       
  • Fast and coupled solution for cooperative mission planning of multiple
           heterogeneous unmanned aerial vehicles
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Weinan Wu, Xiaogang Wang, Naigang Cui This paper studies a problem in which a fleet of heterogeneous fixed-wing unmanned aerial vehicles (UAVs) must identify the optimal flyable trajectory to traverse over multiple targets and perform consecutive tasks. To obtain a fast and feasible solution, a coupled and distributed planning method is developed that integrates the task assignment and trajectory generation aspects of the problem. With specific constraints and a relaxed Dubins path, the cooperative mission-planning problem is reformulated. A distributed genetic algorithm is then proposed to search for the optimal solution, and chromosomal genes are modified to adapt to the heterogeneous characteristic of UAVs. Then, a fixed-wing UAV model with 6 degrees of freedom (DOF) and a path-following method is used to verify this proposed mission-planning method. The simulation results show that the proposed approach obtains feasible solutions and significantly improves the operating rate, with the potential for use in a real mission.
       
  • An approach for estimating perpetual endurance of the stratospheric
           solar-powered platform
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Jun Li, Jun Liao, Yuxin Liao, Huafei Du, Shibin Luo, Weiyu Zhu, Mingyun Lv The high altitude solar-powered airships have been proposed for use as long endurance platforms, for a variety of military and civilian applications. The challenges of perpetual endurance flight require the airship to generate sufficient power over a wide range of operational latitudes so that the aerial vehicle can keep station through high wind events and maintain persistence. This paper provides a theoretical approach to analyzing the perpetual endurance performance of a high altitude solar-powered airship. According to the features of stratospheric airship and the theoretical model, a custom tool is developed using MATLAB computer program when the airship operates in the cruise condition. The effects of the operational latitudes, wind velocities and solar array areas on the energy ratio are numerically investigated in detail, and the required areas of solar array under the conditions of different minimum energy ratio were discussed. The results showed that the solar-powered airships faced severe operational limitations at high latitudes in the winter, especially in the high wind. In addition, a case study was analyzed to demonstrate the effectiveness of this approach to predicting the perpetual endurance region. The results demonstrated that the theoretical approach suggested a pathway towards planning the flight date and location for an airship.
       
  • Loosely-displaced geostationary orbits with hybrid sail propulsion
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Yuan Liu, Jeannette Heiligers, Matteo Ceriotti To overcome the congestion of geostationary orbit slots, previous work proposed to use vertically-displaced, non-Keplerian geostationary orbits by means of continuous low-thrust propulsion in the form of hybrid solar sail and solar electric propulsion (hybrid sail). This work extends and generalizes that concept by loosening the position constraint and introducing a station-keeping box. Sub-optimal orbits are first found with an inverse method that still satisfy the geostationary position constraint (i.e., no station-keeping box), which will be referred to as ideal displaced geostationary orbits. For these sub-optimal orbits, it is found that the hybrid sail saves propellant mass compared to the pure solar electric propulsion case: for solar sail lightness numbers of up to a value of 0.2 and the most favorable time during the year (i.e., at summer solstice), the hybrid sail saves up to 71.6% propellant mass during a single day compared to the use of pure solar electric propulsion. Subsequently, the sub-optimal orbits are used as a first-guess for a direct optimization algorithm based on Gauss pseudospectral transcription, which loosens the position constraint. This enables a more flexible trajectory around the ideal displaced geostationary orbit and lets the solar sail contribute more efficiently to the required acceleration. It therefore leads to a further propellant savings of up to 73.8%. Finally, the mass budget shows that by using by using far-term solar sail technology, the hybrid propulsion system enables an evident reduction in the required initial mass of the spacecraft for a given payload mass with a relatively long mission duration.
       
  • In-flight compound homing methodology of parafoil delivery systems under
           multiple constraints
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Hao Sun, Qinglin Sun, Shuzhen Luo, Zengqiang Chen, Wannan Wu, Jin Tao, Yingping He In order to realize accurate and secure homing control of the parafoil delivery systems under multiple constraints, an in-flight compound homing methodology is designed in this paper. It consists of the modeling of parafoil delivery systems, a trajectory optimization method based on quantum genetic algorithm, a control approach based on active disturbance rejection control. Firstly, the precise model of parafoil delivery system is established by the actual flight data. Then, in order to restrain the wind disturbance, a novel wind identification method is introduced into the trajectory optimization method. Combining the wind identification method and terrain-matching, the proposed trajectory optimization method highlights its improvement from the traditional homing approach. It can not only obtain an optimal trajectory in windy environment, but also maintain the essential advantage of the multiphase homing methodology – great realizability. Then, the ADRC controller is designed. It is applied to resist the varying wind and other disturbance. At last, the hardware-in-the-loop simulation results show that the proposed compound homing methodology can achieve excellent effects both in the trajectory optimization and trajectory tracking. In this paper, the proposed methodology is also compared with the trajectory optimization based on chaos particle swarm optimization method and the PID technology of the trajectory tracking. The results also present huge improvement and wide application prospect.
       
  • Experimental exploration of inlet start process in continuously variable
           Mach number wind tunnel
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Kaikai Yu, Jinglei Xu, Rui Li, Shun Liu, Xiaofei Zhang The flow structures of the inlet in continuously variable Mach number inflow are studied experimentally to evaluate accurately the performance of scramjet inlet during acceleration/deceleration in ground experiments. To break the limitation in which majority of supersonic wind tunnels operate at a fixed Mach number condition, a continuously variable Mach number wind tunnel has been built. The running Mach number of the wind tunnel varies continuously from 2.0 to 3.0 under suction mode. The experiments of the inlet at fixed and variable Mach number inflows are conducted successively in the continuously variable Mach number wind tunnel. In the fixed Mach number experiment, the typical flow structures of the inlet under the unstart/start conditions are captured. The pressure distributions on the lower wall of the inlet, which were obtained from the experiments, are consistent with numerical ones. Thus, the effectiveness and accuracy of the experiments and numerical simulations were verified. In the continuously variable Mach number wind tunnel experiment, we found the inlet suffers from four flow structures. With the exception of typical unstart/start flow structures, the inlet undergoes pseudo unstart/start conditions under the influence of the wind tunnel unstart. By analyzing the pressure and Schlieren result, variations in the flow structures are observed in detail, which can provide useful references for the subsequent experiments in continuously variable Mach number wind tunnels. In particular, pseudo unstart/start conditions must be distinguished from real ones in the case wrong experimental data are obtained in the following experiments.
       
  • Intermittent back-flash phenomenon of supersonic combustion in the
           staged-strut scramjet engine
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Shaohua Zhu, Xu Xu, Qingchun Yang, Yushu Jin The scramjet-powered hypersonic vehicle depends on the sustained and stable supersonic combustion processes, which requires a balance between the flame propagation velocity and the fluid speed. Flame propagation inside a kerosene-fueled staged-strut scramjet engine was experimentally studied in Mach 3.0 incoming flow with the stagnation temperature of 1899 K. The fuel mass flow rate was linearly controlled by an adjustable venturi during the dynamic injection experiment. Two inspection windows were installed on the side and top walls of the combustor respectively. A mirror was utilized to change the light path from the top window to be horizontal to capture the flame structure in the two windows simultaneously. A high-speed imaging camera was employed to capture the flame propagation process described in this short communication. Video imaging showed that the flame was mainly stabilized in the boundary-layer separation region when the upstream equivalence ratio was less than 0.2. In particularly, this short communication reported an intermittent back-flash phenomenon while the fuel equivalence ratio was turned up near to 0.2. The back-flash flame was suggested to be detonation wave by a primary C-J analysis.
       
  • Optimization of bounded low-thrust rendezvous with terminal constraints by
           interval analysis
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Hongliang Ma, Shijie Xu A new indirect resolution method of an optimal control problem is proposed in this paper. And the optimization of the spacecraft low-thrust rendezvous with the fuel-minimum index to a safe region under the collision avoidance constraints is investigated. The objective is to minimize the fuel consumption in a power-limited low-thrust system, which leads to a bounded continuous control. The number of thrust arcs is unknown and the terminal positions in the rendezvous' safe region are unfixed for this optimization problem. The indirect resolution method of the optimal control employs deterministic interval analysis and gradient-based method to obtain the initial guess of the co-state variables. The interval analysis is used to sufficiently split, contract and clip the initial search space. And the gradient-based method is to determine the initial guess for each remained sub-space. Aiming at a low-thrust control system with the upper bound of acceleration of 5e−4 m/s2, numerical results are given to validate the proposed optimization method.
       
  • Efficient coning algorithm design from a bilateral structure
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Chuanye Tang, Long Chen, Jianfeng Chen Many carriers in aerospace applications require high-precision strapdown inertial navigation system (SINS) for navigation. Under complex motion such as maneuver, vibration, etc., the performance of SINS algorithm needs to be paid special attention, since additional algorithm error can be induced due to complex motion. In order to improve the performance of SINS attitude algorithm, a bilateral coning algorithm is presented, which is based on a bilateral correction structure containing only one vector cross-product of which the undetermined coefficient is on both sides. In order to design the bilateral coning algorithm, the classical compressed algorithm coefficient is first given. Then the constraint relationship between the bilateral correction coefficient and the uncompressed correction coefficient is constructed. Further, it is shown that how to design the bilateral correction coefficient according to the constraint relationship. (The maneuver residual error based on the uncompressed correction structure is derived in Appendix A.) After the full analysis and simulation, the bilateral coning algorithm is verified to be very efficient in maneuver environment, for it has low algorithm throughput close to that of the compressed algorithm and high maneuver accuracy close to that of the uncompressed algorithm.
       
  • Multi-objective optimisation of aircraft departure trajectories
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Mengying Zhang, Antonio Filippone, Nicholas Bojdo A multi-objective trajectory optimisation has been developed to minimise multiple environmental impacts (noise and exhaust emissions) from commercial airplanes. Three different non-gradient algorithms are used. First, a parameterization method is established for airplane departure trajectories, with path constraints considered where necessary. Second, a method to parameterize movement in the lateral plane based on a Bézier curve has been proposed to decrease the number of free parameters. The environmental impacts on target areas have been simulated by a comprehensive flight mechanics program. Finally, two posterior selection strategies based on preference function and monetisation approaches are used to evaluate the resulting Pareto solution set. A case study for a departure of an Airbus A320-211 with population distribution of residential communities around Manchester Airport (ICAO code: EGCC) is carried out with three different optimisers. We demonstrate that this simulation framework is able to solve trajectory optimisation problems with multiple simultaneous environmental objectives.
       
  • Optimal morphing – augmented dynamic soaring maneuvers for unmanned air
           vehicle capable of span and sweep morphologies
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Imran Mir, Adnan Maqsood, Sameh A. Eisa, Haitham Taha, Suhail Akhtar This paper investigates autonomous dynamic soaring maneuvers for a small Unmanned Aerial Vehicle (sUAV) having the capability to morph. Dynamic soaring for UAVs have mostly been confined in literature to fixed configurations. In order to analyze the extent to which dynamic soaring is influenced by different morphologies, an innovative concept of integrating dynamic soaring with morphing capabilities is introduced. Moreover, optimal soaring trajectories are generated for two basic wing morphologies: variable sweep and variable span. Three-dimensional point-mass UAV equations of motion and nonlinear wind gradient profile are used to model the flight dynamics. Parametric characterization of the key performance parameters is performed to determine the optimal platform configuration during various phases of the maneuver. Results presented in this paper indicate 15% lesser required wind shear by the proposed span morphology and 14% lesser required wind shear by the proposed sweep morphology, in comparison to their respective fixed wing counterparts. This shows that the morphing UAV can perform dynamic soaring in an environment, where fixed configuration UAVs might not, because of lesser available wind shears. Apart from this, span morphology reduced drag by 15%, lift requirement by 11% and angle of attack requirement by 20%, whereas increased the maximum velocity by 6.2%, normalized energies by 9% and improved loitering parameters (approximately 10%), in comparison to fixed span configurations. Similarly, sweep morphology guaranteed 20% drag reduction, 16% lesser angle of attack requirement and improved loitering performance over the fixed sweep configurations. The results achieved from this study strongly support the idea of integrating dynamic soaring with morphing capabilities and its potential benefits.
       
  • Aerodynamic model-based robust adaptive control for close formation flight
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Qingrui Zhang, Hugh H.T. Liu This paper presents an aerodynamic model-based robust adaptive control algorithm for close formation flight. The leader aircraft is assumed to be at level and straight flight which characterizes the most common scenario for close formation flight. The formation aerodynamic effects are assumed to be unknown, but an online formation aerodynamic model is available to predict those effects. In light of the online formation aerodynamic model, a robust adaptive control algorithm is thereafter developed on the follower aircraft to counteract the unknown formation aerodynamic effects and obtain highly accurate formation tracking performance. The proposed control algorithm is composed of a baseline controller and an integrator-augmented robust adaptive controller, which can efficiently deal with both matched and mismatched formation aerodynamic effects and external disturbances. The major advantage of the proposed design is that it can achieve at least ultimate bounded tracking control with certain transient performance guaranty. The efficiency and robustness of the proposed control design are eventually validated via numerical simulations of close formation flight at two different scenarios.
       
  • Angular momentum of free variable mass systems is partially conserved
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Angadh Nanjangud, Fidelis O. Eke Variable mass systems are a classic example of open systems in classical mechanics with rockets being a standard practical example. Due to the changing mass, the angular momentum of these systems is not generally conserved. Here, we show that the angular momentum vector of a free variable mass system is fixed in inertial space and, thus, is a partially conserved quantity. It is well known that such conservation rules allow simpler approaches to solving the equations of motion. This is demonstrated by using a graphical technique to obtain an analytic solution for the second Euler angle that characterizes nutation in spinning bodies.
       
  • Flow separation control over an airfoil using dual excitation of DBD
           plasma actuators
    • Abstract: Publication date: August 2018Source: Aerospace Science and Technology, Volume 79Author(s): Abbas Ebrahimi, Majid Hajipour This paper investigates flow separation control over an airfoil using dual excitation of DBD plasma actuators as a novel approach. Large eddy simulation is adopted to capture vortical structures within the airfoil wake. Power spectral density and dynamic mode decomposition analyses have been utilized to identify local and global oscillatory behavior associated with flow structures of the wake. Three controlled cases are considered in the present study. In the first case, the wake mode frequency (i.e., the frequency of natural vortex shedding) is used to excite separated shear layers at both the upper surface and the trailing edge of the airfoil, simultaneously. In the second case, the excitation frequency of the trailing edge actuator is increased to sixth multiples of the wake mode, while the other actuator excites the flow same as the first case. In the third case, excitation with frequency of the wake mode is only applied to the upper surface separated shear layer and no excitation is exerted at the trailing edge. According to the results, actuations manipulate the shear layers instabilities and modify the wake patterns remarkably. In all controlled cases, breakdown of the upper surface shear layer takes place closer to the separation point and also less strong vortices shed from the trailing edge compared to the baseline flow. It is revealed that the coherency of vortices within the wake region is not quite the same for all cases and the least coherency of vortical structures is observed in the first case. The maximum values of lift-to-drag ratio and lift coefficient is achieved in the first and second cases, respectively.
       
  • Ethylene flame-holding in double ramp flows
    • Abstract: Publication date: Available online 12 July 2018Source: Aerospace Science and TechnologyAuthor(s): Eric Won Keun Chang, Sungmo Yang, Gisu Park, Hojin Choi In this work, ethylene flame-holding in supersonic flows was investigated using a shock tunnel. The experiments were conducted at flow stagnation temperatures ranging from 1270 to 1810 K. The two-dimensional test model consisted of a double-ramp inlet and a constant-area combustor with a recessed wall cavity. The two fuel injectors were located at the inlet and the other upstream of the cavity. Shadowgraph and flame chemiluminescence images were captured for optical visualization. The inlet injection images showed various flame-holding patterns. At 1270 K, the flame was not maintained. At 1540 K, the flame was maintained inside the cavity, and the condition provided continuous combustion during the steady flow. At 1810 K, strong flame signals were observed from the inlet to the cavity and downstream. At 1540 K, the inlet injection with a low fuel pressure showed a gradual flame quenching in the cavity during flow establishment. On the other hand, the same injection in the combustor showed flame-holding in the shear layer above the cavity. The results showed that the flame patterns are strongly influenced by the flow stagnation temperature and the location of fuel-injection.
       
  • Criteria for designing low-loss and wide operation range variable inlet
           guide vanes
    • Abstract: Publication date: Available online 12 July 2018Source: Aerospace Science and TechnologyAuthor(s): Hengtao Shi, Baojie Liu, Xianjun Yu Critical factors influencing the variable inlet guide vane (VIGV) profile loss at high incidence condition were studied by using numerical methods and a practical design criterion for designing wide low-loss operation range VIGVs in axial-flow compressor was proposed. At first, to acquire research samples, a series of airfoils with different shapes were generated for two selected representative VIGV cascade cases. Steady simulations based on Reynolds-Averaged Navier-Stokes method, carried out by commercial software CFX and validated with experimental data after grid independent study, were first conducted to predict the aerodynamic performances, the surface velocity distributions and the boundary-layer behaviors of the generated airfoils. Based on the simulated results, the influences of geometric parameters on airfoil performances were analyzed and the geometric features of low-loss VIGV airfoil were revealed. Further analysis indicated that the magnitude of airfoil loss at high incidence condition were mainly influenced by the scales of two boundary-layer separation regions: one at the leading edge caused by the high adverse pressure gradient induced by the suction spike and the other one caused by the adverse pressure gradient induced by the re-acceleration flow. To reveal the influence of the suction spike and the re-acceleration flow on the scales of separation regions, two practical parameters Dspike and Are were defined. It was found that there exists an optimized range of the Dspike and Are which could keep the separation flow to a small scale at high incidence condition and can be used as a surface velocity design criterion for designing wide low-loss operation range VIGVs. Moreover, the methods for choosing the airfoil geometric parameters to achieve the preferred surface velocity distribution were discussed. Finally, the developed design criterion was used to guide the airfoil modification of an axial-flow compressor VIGV and achieved an average of 19%, 52% and 73% loss coefficient reduction at three high stagger angle operating points, which confirms the applicability and effectiveness of the design criterion in three-dimensional environment.
       
  • Efficient uncertainty quantification for a hypersonic trailing-edge flap,
           using gradient-enhanced kriging
    • Abstract: Publication date: Available online 11 July 2018Source: Aerospace Science and TechnologyAuthor(s): Sudip Bhattrai, Jouke H.S. de Baar, Andrew J. Neely We present a numerical study on the uncertainty quantification (UQ) of aerodynamic forces acting on a hypersonic trailing-edge flap model, as a result of input uncertainties in the experimental boundary conditions. The complex fluid–thermal-structural interaction on aerodynamic surfaces of a hypersonic flight vehicle and fluctuations in flow conditions result in uncertainties in their aerodynamic characteristics. We run the numerical simulations in US3D to quantify these uncertainties. Altogether four input uncertain parameters—inlet flow velocity, density, temperature, and the model wall temperature—are considered. We obtain the aerodynamic forces from the primal solve, as well as gradient information from a dedicated sensitivity solver. We compare the surrogate-based UQ analysis using kriging as well as gradient-enhanced kriging (GEK), accounting for significant observation errors in the gradients, and quantify the accuracy of the output probability density function (PDF). The accuracy of the predicted output PDF converges faster for GEK than for kriging, implying the importance of the gradient information in order to reduce the computational cost—in the present case, the computational cost is reduced by a median speed-up of roughly 3.0 by exploiting the gradient information available from the sensitivity solver.
       
  • Dynamic surface control design of post-stall maneuver under unsteady
           aerodynamics
    • Abstract: Publication date: Available online 11 July 2018Source: Aerospace Science and TechnologyAuthor(s): Yongxi Lyu, Yuyan Cao, Weiguo Zhang, Jingping Shi, Xiaobo Qu This paper presents an efficient method that overcomes the problem of the control design of the post-stall maneuver under unsteady aerodynamics. On the basis of adequate data of the large amplitude oscillation experiment device in wind tunnel test, the unsteady aerodynamics model with nonlinearity, coupling and hysteresis is established by the improved Extreme Learning Machine (ELM) method. Considering the nonlinearity of the longitudinal model of the advanced fighter and the aerodynamics characteristics of the post-stall maneuver, the control law under large attack angle is designed combining the backstepping method and the daisy chain allocation method. The first order filter is adopted to prevent the “differential explosion” problem. The designed control allocation law guarantees that the conventional surfaces and the vector nozzle deflect coordinately within the position limits and the rate limits. The Radial Basis Function (RBF) network is applied to model the uncertainty, and the stability of the proposed control law which considering the uncertainty is also proved. Digital simulations of the typical “Cobra” maneuver under the unsteady aerodynamics are completed with comparisons under different conditions. Simulations results verify the validity of the proposed control law under unsteady aerodynamics and the aerodynamics uncertainty.
       
  • Rotorcraft comprehensive code assessment for blade-vortex interaction
           conditions
    • Abstract: Publication date: Available online 11 July 2018Source: Aerospace Science and TechnologyAuthor(s): Massimo Gennaretti, Giovanni Bernardini, Jacopo Serafini, Gianluca Romani The scope of this paper is the presentation of the computational methodologies applied in the comprehensive code for rotorcraft developed in the last years at Roma Tre University, along with the assessment of its prediction capabilities focused on flight conditions characterized by strong blade-vortex interactions. Boundary element method approaches are applied for both potential aerodynamics and aeroacoustics solutions, whereas a harmonic-balance/modal approach is used to integrate the rotor aeroelastic equations. The validation campaign of the comprehensive code has been carried out against the well-known HART II database, which is the outcome of a joint multi-national effort aimed at performing wind tunnel measurements of loads, blade deflection, wake shape and noise concerning a four-bladed model rotor in low-speed descent flight. Comparisons with numerical simulations available in the literature for the same test cases are also presented. It is shown that, with limited computational cost, the results provided by the Roma Tre aero-acousto-elastic solver are in good agreement with the experimental data, with a level of accuracy that is in line with the state-of-the-art predictions. The influence of the vortex core modeling on aerodynamic predictions and the influence of the inclusion of the fuselage shielding effect on aeroacoustic predictions are discussed.
       
  • Study of boundary layer transition on supercritical natural laminar flow
           wing at high Reynolds number through wind tunnel experiment
    • Abstract: Publication date: Available online 11 July 2018Source: Aerospace Science and TechnologyAuthor(s): Jiakuan Xu, Ziyuan Fu, Junqiang Bai, Yang Zhang, Zhuoyi Duan, Yanjun Zhang In order to achieve the goal of green aviation, energy conservation and emission reduction, laminar flow design technology has become a hot research topic. For transonic airliners, supercritical natural laminar flow wing design technology will significantly improve the aerodynamic performance(reduce flight drag, decrease fuel consumption and pollutant emissions). In this paper, airfoil optimization design system is applied to design the supercritical natural laminar flow airfoils based on high-precision boundary layer transition prediction technique. Then, three-dimensional layout of supercritical natural laminar flow wing is formed. Numerical simulations have been conducted to verify the laminar flow properties. In addition, the aerodynamic model with ratio of 1: 10.4 is processed to measure boundary layer transition phenomena in the high speed and low turbulence wind tunnel in Netherland. Temperature sensitive paint (TSP) technique is used to photograph laminar-turbulent distribution at different Mach numbers, Reynolds numbers and angels of attack. In the following content, boundary layer transition properties of the supercritical natural laminar flow wing are analyzed using TSP results and CFD simulations. Finally, key factors of supercritical natural laminar wing design and corresponding boundary layer transition properties are summarized. In addition, the research about transition properties of supercritical natural laminar flow wing at high Reynolds numbers have guiding significance for aircraft designers and transition researchers.
       
  • Numerical evaluation of station-keeping strategies for stratospheric
           balloons
    • Abstract: Publication date: Available online 11 July 2018Source: Aerospace Science and TechnologyAuthor(s): Sai Sudha Ramesh, Juanli Ma, Kian Meng Lim, Heow Pueh Lee, Boo Cheong Khoo The trajectory control of stratospheric balloons poses a great challenge, given their importance in scientific explorations and military applications. This has led to the investigation of several trajectory control methods, which aim to retain the balloon system within a specific region. In particular, the use of a control device tethered to the main balloon is required to provide sufficient lateral forces to counteract the air drag on the main balloon. The present study evaluates the performance of two kinds of balloon systems namely, the dual-balloon and balloon–stratosail systems that have a control device tethered to the main balloon. The study compares their performances in the context of realistic wind conditions, and presents the best working range for each of the system, which may be useful in improvising the design of control devices for future applications.
       
  • Nonlinear gain-scheduled flight controller design via stable manifold
           method
    • Abstract: Publication date: Available online 10 July 2018Source: Aerospace Science and TechnologyAuthor(s): Anh Tuan Tran, Noboru Sakamoto, Koichi Mori This research presents a nonlinear gain-scheduled flight controller design method via a stable manifold theory in order to handle the nonlinearities of the F-18 High Alpha Research Vehicle due to the change in the aerodynamic characteristics at different angles of attack and the airspeed variation. The designed longitudinal flight control system consists of a nonlinear gain-scheduled stabilization augmentation system which is designed using the stable manifold method, and a linear gain-scheduled control augmentation system which consists of proportional and integral gains. The nonlinear longitudinal flight controller is verified in a 6 degree-of-freedom simulator.
       
  • The optimization and flow diagnoses for a transonic fan with stage flow
           condition
    • Abstract: Publication date: Available online 10 July 2018Source: Aerospace Science and TechnologyAuthor(s): Huanlong Chen, Yong Qin, Ruoyu Wang The redesign and optimization of a low-aspect ratio transonic fan is implemented in this study. An advanced 3D aerodynamic optimization design system is adopted, while flow diagnostic methods are employed to discuss the transonic flow in the blade passages. On the basis of maintaining high aerodynamic efficiency, the study seeks to improve the pressure ratio and through-flow capability of the redesigned fan stage. Furthermore, the dynamic principle for the redistribution of passage flow due to geometry change is revealed. In comparison with the prototype, the total pressure ratio of the redesigned fan is increased by 7.54% at the design point, while its mass flow rate and adiabatic efficiency are raised by 6.30% and 1.25%, respectively. Additionally, a wider high-efficiency operation range is also achieved by the optimization. Under stage flow condition, the control of shock wave at the rotor tip and the removal of low momentum fluid in the stator corner are the two keys in improving the aerodynamic performance of the redesigned fan. Moreover, tangential lean of the stator blade has also succeeded in delaying corner flow separations. Further research for these design techniques would give potential to expand the design system for transonic fan/compressor with low-aspect ratios.
       
  • Interval analysis of the standard of adaptive cycle engine component
           performance deviation
    • Abstract: Publication date: Available online 10 July 2018Source: Aerospace Science and TechnologyAuthor(s): Min Chen, Jiyuan Zhang, Hailong Tang The deviation of engine component performance has great impact on the Adaptive Cycle Engine (ACE) overall performance and task adaptability. To make ACE performance reach the mission requirement, proper standard of component performance deviation (CPD) should be given in advance. In this paper, an approach based on the first order Taylor series expansion has been proposed and applied to set the standard of CPD without large amounts of calculation. This approach is an inversion process of the normal interval analysis and can take the distinction between the impacts of CPD indexes into consideration. Fifteen component performance parameters and four important operating conditions are investigated. The results show that the distinction between the impacts of CPD indexes and different operating conditions is obvious. Compared with setting uniform standard for all CPD indexes, this method can better utilize component characteristics and make the standard reasonable and economical. The standard of CPD can be derived within 10 times of off-design point calculation through this method, which is much less than 32768 times of calculation for the vertex method. This method is universal and can be applied to setting standard for the CPD of other type of gas turbine engines.
       
  • Efficient numerical algorithm of profust reliability analysis: An
           application to wing box structure
    • Abstract: Publication date: Available online 10 July 2018Source: Aerospace Science and TechnologyAuthor(s): Kaixuan Feng, Zhenzhou Lu, Chao Pang, Wanying Yun In aerospace engineering, the reliability analysis technique attracts increasing attention from many structure designers. Compared with the conventional reliability analysis, the probability and fuzzy state assumption (profust) reliability analysis is proposed as a more comprehensive and objective theory to evaluate the structural safety. Because of great computational burden of the existing methods in estimating profust failure probability, an efficient numerical algorithm is developed in this paper. The proposed method is based on an equivalent transformation of the profust failure probability, then the profust failure probability can be rewritten as the form of a series of conventional failure probabilities which have similar constructions. The subset simulation method is employed to compute all the conventional failure probabilities by using a set of samples repeatedly. Next, this method is applied to estimate the profust failure probability of a wing box structure. The calculation results indicate that the proposed method can reduce the computational cost dramatically with acceptable precision.
       
  • Aeroelastic analysis of functionally graded rotating blades reinforced
           with graphene nanoplatelets in supersonic flow
    • Abstract: Publication date: Available online 10 July 2018Source: Aerospace Science and TechnologyAuthor(s): Reza Bahaadini, Ali Reza Saidi In this study, the aeroelastic analysis of functionally graded (FG) multilayer graphene platelet reinforced polymer composite (GPLRPC) rotating blades under supersonic flow is investigated. It is considered that the graphene platelet (GPL) nanofillers are distributed in the matrix either uniformly or non-uniformly along the thickness direction. Four GPL distribution patterns namely, U-GPLRPC, Λ-GPLRPC, X-GPLRPC and O-GPLRPC are considered. The effective material properties of GPLRPC layers are obtained via the modified Halpin–Tsai micromechanics model and the rule of mixture. Based on the first-order shear deformation theory, the dynamic equations of thin-walled blades reinforced with GPL are obtained using extended Hamilton's principle. The aerodynamic pressure is assumed in accordance with the quasi-steady supersonic piston theory. The extended Galerkin method (EGM) is employed to transform the coupled equations of motion to a general eigenvalue problem. The influences of rotating speed, GPL distribution, GPL weight fraction, geometry of GPL nanofillers, geometric parameters and Mach number on the natural frequencies of the system are studied. The results indicate that the Λ-GPLRPC distribution pattern predicts the highest natural frequencies for the composite blade. Also, the natural frequencies of the composite blade significantly increase by adding a small amount of GPL to the polymer matrix.
       
  • Technology and opportunities of photon sieve CubeSat with deployable
           optical membrane
    • Abstract: Publication date: Available online 10 July 2018Source: Aerospace Science and TechnologyAuthor(s): Hyun Jung Kim, Shravan Hariharan, Matthew Julian, David Macdonnell A photon sieve (PS) is a revolutionary optical instrument that provides high resolution imaging at a fraction of the weight of typical telescopes, with an areal density of 0.3 kg/m2 compared to 25 kg/m2 for the James Webb Space Telescope. The photon sieve is a variation of a Fresnel Zone Plate consisting of many small holes arranged in a series of concentric rings. The sieve works by diffracting light of a certain wavelength to a specified focal point for imaging, so that only a specific wavelength can be imaged. Moreover, the better image contrast and higher signal-to-noise ratios come from suppressing higher diffracted orders by apodizing the number of pinholes in the outer rings. Finally, a photon sieve requires less supports and can withstand more deformation without a reduction in the imaging qualities.Due to these properties, various groups have created PS CubeSats for Earth and Sun imaging at a low cost and weight specifically using deployable technology. A team at the Air Force Research Laboratory created a design and prototype of a mechanism that deploys a 20 cm diameter photon sieve. The United States Air Force Laboratory used a similar design to create a CubeSat-based deployable photon sieve. The team at NASA Langley Research Center has researched photon sieves for conducting an Earth-observing experiment using LIDAR (Light Detection and Ranging) with a higher signal-to-noise ratio benefit from the PS. This paper provides a state of the art overview on existing PS CubeSat technology with deployable structures and applications. Especially, the paper introduces PS for LIDAR applications and discusses the CubeSat-based PS challenge being worked at the NASA Langley Research Center.
       
  • Switched propulsion force libration control for the low-thrust space tug
           system
    • Abstract: Publication date: Available online 10 July 2018Source: Aerospace Science and TechnologyAuthor(s): Xin Sun, Rui Zhong The number of micro-satellites launched by commercial rockets and designed by universities and institutions is experiencing rapid growth, inevitably increasing the amount of the space debris of the same size. This paper adopts a low-thrust tethered space tug system to achieve debris deorbit. A switched low-propulsion force control method using only two constant-thrust modes to achieve both deorbit and libration control is presented. This kind of control method benefits from its robustness and low demand on the output accuracy of the thruster. The harmonic-like libration dynamics of the tethered space tug system around the local horizontal configuration is discussed and the stability of the control method is proved. Moreover, the sufficient condition for the switching sustainability is presented. Afterwards, the control effects of such a system are illustrated using numerical simulations. A modified control law to adapt practical demands shows the flexibility of the switching control methodology.
       
  • Comparison of studies on flow and flame structures in different swirl
           combustors
    • Abstract: Publication date: Available online 3 July 2018Source: Aerospace Science and TechnologyAuthor(s): L.X. Zhou Swirling gas combustion and two-phase combustion (spray-air or particle-air combustion) are widely encountered in gas-turbine combustors and internal combustion engines. In experimental studies of practical combustors frequently it is difficult to get the detailed information inside the combustors. Most of numerical simulation is Reynolds-averaged (RANS) modeling, which cannot give detailed flow and flame structures. Some investigators reported their results using large-eddy simulation (LES) with different combustion models. The present authors did systematic LES studies on swirling gas combustion and two-phase combustion using second-order moment (SOM) and EBU combustion models. The statistic results are assessed by the measurement results. The instantaneous results show the flow and combustion behavior in different swirl combustors.
       
  • Verification and application of a mean flow perturbation method for jet
           noise
    • Abstract: Publication date: Available online 3 July 2018Source: Aerospace Science and TechnologyAuthor(s): Swagata Bhaumik, Datta V. Gaitonde, S. Unnikrishnan, Aniruddha Sinha, Hao Shen The stability properties of basic states are often elucidated by examining the evolution of small disturbances. Such studies have recently been successfully applied to mean turbulent states, obtained through averaging of experimental measurements or Large-Eddy Simulations (LES), for both wall-bounded as well as free shear flows. Typically, the equations are employed using the disturbance form of the equations. To circumvent the necessity to linearize the governing equations, an especially tedious task for viscous and turbulent closure terms, Touber and Sandham (2009) [21], proposed an approach that achieves the same purpose by solving the full Navier–Stokes (NS) equations, with a forcing term to maintain mean flow invariance. The method places no restrictions, such as slow streamwise variations, on the underlying basic state. The goals of the current work are to first verify this mean flow perturbation (NS-MFP) technique and then apply it to the problem of jet noise. For the first thrust, we show that when the basic state is appropriately constrained, the technique reverts to Linear, Parabolized and Global stability methods. The method is then verified by reproducing the growth of unstable modes in an inviscid Mach 6 entropy layer. The application to jet noise considers subsonic Mach 0.9 and perfectly expanded supersonic Mach 1.3 round jets. The results are compared with those from Parabolized Stability Equations (PSE) and LES solutions, respectively, considering monochromatic and multi-frequency perturbations. The NS-MFP method successfully reproduces key features of the modal response, including Strouhal number dependent directivity of noise radiation. Aspects related to the manner in which the mean basic state is obtained, whether from LES or Reynolds-averaged Navier–Stokes (RANS) equation are also explored. In particular, the sensitivity of the perturbation to whether the eddy viscosity is included or not, is examined in reference to maximum intensity of pressure fluctuation, directivity of noise radiation and the rate of fall-off of the spectra at higher Strouhal numbers. The results indicate that a closer match on the noise-radiation characteristics is obtained when effects of eddy-viscosity on the disturbances are neglected.
       
  • Design of mistuning patterns to control the vibration amplitude of
           unstable rotor blades
    • Abstract: Publication date: Available online 2 July 2018Source: Aerospace Science and TechnologyAuthor(s): Roque Corral, Oualid Khemiri, Carlos Martel Flutter onset is one of the major causes for increased vibration levels in low pressure turbine (LPT) rotor blades. This paper describes the design process and the experimental testing of intentional mistuning patterns specifically chosen to show the possibility to control the flutter characteristics of an LPT rotor. The Asymptotic Mistuning Model (AMM) methodology is used to select the intentional mistuning patterns. The AMM formulation incorporates elastic and aerodynamic data from detailed FEM and CFD computations, and measured values of the rotor blades intrinsic mistuning. The intentional mistuning patterns are implemented in the rotor by mounting small masses at the tip-shroud of the blades, and the effect of these small masses is also introduced in the AMM description. Two intentional mistuning patterns are selected. The classical alternate mistuning pattern, designed to fully suppress flutter, and a second intentional mistuning pattern that is designed with the idea of halving the vibration amplitude of the tuned unstable rotor. This second mistuning pattern demonstrates that, through the implementation of the appropriate intentional mistuning pattern, flutter cannot only be suppressed but also modulated. The two mistuned LPT rotors were tested in a free flutter experiment at a high speed rotating wind-tunnel, and the experimental results showed a good agreement with the AMM stability predictions. This is the first time, to our knowledge, that the possibility to control flutter through intentional mistuning has been experimentally validated in a rotating rig. The AMM is also applied to evaluate the effect of the aerodynamic coupling in the stability calculations of the mistuned rotors, and the AMM results are compared with high fidelity numerical calculations. It is shown that, despite its very reduced formulation, the AMM produces quite accurate stability predictions, and that it is essential to take into account the aerodynamic coupling; if it is not considered then the instability level of the mistuned rotors can be substantially underestimated.
       
  • Fuzzy adaptive non-affine attitude tracking control for a generic
           hypersonic flight vehicle
    • Abstract: Publication date: Available online 2 July 2018Source: Aerospace Science and TechnologyAuthor(s): Yuhui Wang, Mou Chen, Qingxian Wu, Jun Zhang A fuzzy adaptive non-affine attitude tracking control method is proposed for a generic hypersonic flight vehicle (HFV). Due to the complexities of the hypersonic flows and nonlinear dynamics, the aerodynamic coefficients of the HFV are dependent not only on the attack of angle, sideslip angle, angular rates, and Mach number, but also on the deflection angles of the control surfaces. This cause the attitude tracking control problem becomes a non-affine multi-input–multi-output (MIMO) one. By analyzing the characteristics of the aerodynamic coefficients, it can be found that the non-affine terms have a great influence on the attitude dynamics and should not be ignored. Then, a non-affine MIMO attitude tracking controller is designed using fuzzy sliding mode adaptive techniques with consideration of the non-affine nonlinear aerodynamic coefficients. The proposed controller has good practicability because it does not need to know the exact bound values of the uncertainties, unmodeled dynamics, and external disturbances. Finally, simulation results show that the attitude angles can track the desired signals robustly and asymptotically under the control.
       
  • Synthesis of attitude control for statically unstable hypersonic vehicle
           with low-frequency aero-servo-elastic effect
    • Abstract: Publication date: Available online 2 July 2018Source: Aerospace Science and TechnologyAuthor(s): Minnan Piao, Zhihong Yang, Mingwei Sun, Jian Huang, Zenghui Wang, Zengqiang Chen In this paper, an integrated attitude control scheme is proposed for a statically unstable hypersonic vehicle (HSV) with low-frequency aero-servo-elastic effect. Linear active disturbance rejection control (LADRC) is designed for the pitch angle to address the strong uncertainties and coupling effects. For the particular aero-servo-elastic effect with low frequency, a hybrid phase and gain stabilization technique is embedded into the LADRC framework to suppress the structural modes, which can reduce the phase loss around the crossover frequency. To achieve satisfactory tracking performance and robustness, a non-smooth H∞ optimization approach is applied to tune the controller gains, which simplifies the tuning and gain scheduling process. Monte Carlo simulation results demonstrate the effectiveness of the proposed control scheme.
       
  • Cooperative interception strategy for multiple inferior missiles against
           one highly maneuvering target
    • Abstract: Publication date: Available online 2 July 2018Source: Aerospace Science and TechnologyAuthor(s): Wenshan Su, Hyo-Sang Shin, Lei Chen, Antonios Tsourdos This paper proposes a novel cooperative guidance strategy, which aims to intercept one highly maneuvering target with multiple inferior missiles. In the scenario of interest, both the missiles and target are assumed to have bounded maneuverability, and the guidance goal is to make the joint reachable set of interceptors cooperatively cover the target maneuvering range. Under this guidance scheme, a preprogrammed covering strategy and an adaptive covering strategy are designed for the missile teams without and with communication capability respectively. The former attempts to specify different subsets of the target maneuvering range to different missiles as the expected reachable sets, while the latter aims to coordinate the expected reachable sets of different missiles dynamically according to the changing engagement situation. Considering the disadvantage of inferior maneuverability, the inherent limitations of the proposed guidance scheme are discussed. Numerical simulations with different target maneuvering modes demonstrate the prominent performance improvements of cooperative strategy over the traditional guidance laws.
       
  • Numerical investigations of ducted fan aerodynamic performance with
           tip-jet
    • Abstract: Publication date: July 2018Source: Aerospace Science and Technology, Volume 78Author(s): Jie Chen, Lei Li, Guoping Huang, Xin Xiang Tip-jet technology has the potential value for application in vertical take-off and landing or short take-off and landing concept aircraft. The main objective of this work is to present a rapid prototyping method to model the power of the tip-jet during the concept design phase, and to investigate the aerodynamic performance of a ducted fan with tip-jet in hover through numerical experiments. The calculated data of the rapid method was compared to the numerical results, while the comparative analysis of the performances of an open fan, a ducted fan and a ducted fan with tip-jet were carried out. The results indicate that the fan lift of the ducted fan with tip-jet was augmented by the jets which formed the Coanda effect on the suction surface of the blade to increase the circulation of the blade. The figure of merit of the ducted fan with tip-jet was reduced and slightly affected by the nozzle area. The flow field represents the same flow features when the nozzle works in subsonic to supersonic operational conditions.
       
  • Development and experimental validation of a multi-algorithmic hybrid
           attitude determination and control system for a small satellite
    • Abstract: Publication date: July 2018Source: Aerospace Science and Technology, Volume 78Author(s): Dae Young Lee, Hyeongjun Park, Marcello Romano, James Cutler Advanced missions of satellites are increasingly demanding more accurate and robust attitude maneuvering capabilities. However, it is difficult to achieve especially for small satellites due to limited hardware resources of sensors, actuators, and processors. In this paper, to achieve the desired performance, a multi-algorithmic hybrid attitude determination and control system (ADCS) that utilizes a family of control and estimation algorithms is developed and implemented in numerical simulations and experiments for a small satellite. The hybrid automaton framework of the ADCS is designed to accomplish the desired performance with the limited hardware capability by switching the control and estimation algorithms effectively for given situations in space. The performance of the hybrid ADCS is evaluated through numerical and hardware-in-the-loop simulations that are based on a three-dimensional air-bearing testbed, CubeSat Three-Axis Simulator (CubeTAS). Simulation and experimental results demonstrate the effectiveness of the multi-algorithmic hybrid ADCS. The significance of this paper is in demonstrating that the hybrid automaton framework can be an effective approach to handle operational situations in space. It also provides a design reference for a small satellite ADCS.
       
  • An improved propeller design method for the electric aircraft
    • Abstract: Publication date: July 2018Source: Aerospace Science and Technology, Volume 78Author(s): Song Xiang, Yuan-qiang Liu, Gang Tong, Wei-ping Zhao, Sheng-xi Tong, Ya-dong Li In this paper, an improved propeller design method for the electric aircraft was presented. For a given operative condition and profile distribution along the blade, the present method can determine the chord and pitch angle distribution of the blade, together with its efficiency and its torque and thrust coefficients of the maximum efficiency propeller. According to the flight velocity, thrust and rotate speed of cruise condition, the propeller of an electric aircraft was designed using the present method. Wind tunnel test of scaled model of propeller (diameter 0.96 m) was carried out. The test results show that present method was suitable to design the propeller of the electric aircraft.
       
  • A layered fluctuation model of electron density in plasma sheath and
           instability effect on electromagnetic wave at Ka band
    • Abstract: Publication date: July 2018Source: Aerospace Science and Technology, Volume 78Author(s): Bo Yao, Xiaoping Li, Lei Shi, Yanming Liu, Bowen Bai The effects of plasma sheath on communication signals are not only power attenuation but also multiplicative noise addition because of the sheath's instability. The fluctuation properties of time-varying electron density are crucial to comprehensively understand the blackout problem. In this paper, the fluctuation laws of time-varying electron density are first comprehensively revealed in space–time–frequency domain. A layered fluctuation model of time-varying electron density is then proposed based on these fluctuation laws. The effects of dynamic plasma sheath on electromagnetic (EM) waves at Ka band are calculated by Monte Carlo quasistatic EM numerical method. Results show that the amplitude and phase of time-varying transmission coefficient both follow Gaussian distribution, whereas the spectrum curves follow a bi-Gauss function because of the effect of second mode instability in the hypersonic boundary layer. Furthermore, the means of amplitudes increase with the increasing of the incident EM wave frequency and the decreasing of the peak electron density, while the standard deviations decrease with the increasing of incident EM wave frequency, the decreasing of the peak electron density and the decreasing of electron density standard deviation.
       
  • Buckling analysis of two-directionally porous beam
    • Abstract: Publication date: July 2018Source: Aerospace Science and Technology, Volume 78Author(s): Haishan Tang, Li Li, Yujin Hu In this paper, buckling analysis of two-directionally porous beam is conducted. Based on the available results of Young's modulus and mass density via Gaussian random field theory, a new two-directionally porous beam model is developed. With the help of Euler–Bernoulli beam theory and minimum total potential energy principle, the equilibrium equations for nonlinear and linear buckling are derived. The numerical solutions of critical buckling loads for different porosity distribution patterns can be obtained by generalized differential quadrature method. The final numerical results exhibit that more porosities near the middle surface or the two edges of beam can lead to a larger critical buckling load when the same total volume fraction of porosity is in different porosity distribution patterns. The effect of porosity distribution in thickness direction is more dominated on the critical buckling load than that of the axial porosity distribution. Moreover, the critical buckling load becomes more sensitive to aspect ratio of beam and total volume fraction of the porosity when increasing mode number. The critical buckling load of two-directionally porous beam depends not only on bending coefficient (like the one-directionally porous beam), but also on first and second derivatives of the bending coefficient.
       
  • Numerical and experimental investigation of fitting tolerance effects on
           damage and failure of CFRP/Ti double-lap single-bolt joints
    • Abstract: Publication date: July 2018Source: Aerospace Science and Technology, Volume 78Author(s): Yuejie Cao, Zengqiang Cao, Yangjie Zuo, Lubin Huo, Jianping Qiu, Duquan Zuo CFRP/Ti bolted joints are increasingly used in aircraft structures. Optimizing the joint design is vital for overall composite structure designs. Therefore, a progressive damage model was developed for investigating the effects of clearance and interference sizes on the damage and failure of CFRP/Ti double-lap, single-bolt joints under quasi-static loads, in which the improved three dimensional Hashin failure criterion and Tan degradation rules were used through an ABAQUS user-define-field (USDFLD) subroutine. The corresponding quasi-static tensile tests and fatigue tests were also conducted. Joints strength were evaluated and failure mechanism was discussed. Numerical results showed that the matrix compression failure dominated the joint failure mode. Joint ultimate strength decreased gradually with the increase of clearance sizes, while joint bearing strength and stiffness exhibited an increase with interference sizes at first and then decreased rapidly due to the initial installation damage. Moreover, the maximum strength was achieved at the interference size of 0.5%. Those results were in well agreement with corresponding experimental results. In addition, interference sizes were also revealed a correlation with the fatigue life of the joints. The study presented here will be useful for optimization of composite structure designs.
       
  • Virtual-command-based model reference adaptive control for abrupt
           structurally damaged aircraft
    • Abstract: Publication date: July 2018Source: Aerospace Science and Technology, Volume 78Author(s): Jing Zhang, Xiaoke Yang, Lingyu Yang Although a high-gain learning rate can offer ideal tracking performance in adaptive control in theory, it can also lead to high-frequency oscillations in practice due to the unmodeled dynamics of the system. In aircraft structural damage scenarios, the strong uncertainty and the safety-critical nature of the problem make this conflict critical. In this paper, a novel virtual-command-based model reference adaptive control (MRAC) scheme for flight control is proposed. In the new framework, the direct relationship between the learning law and the actual tracking error is broken; instead, a virtual command is introduced as the input to the standard MRAC controller. The key feature is that even when the virtual tracking error is large, the actual tracking error can be maintained within a small range; thus, the MRAC learning rate does not necessarily need to be large to suppress the virtual transient tracking error, which is greatly beneficial for the robustness of the MRAC controller. The proposed method is illustrated by the attitude control of the 6-DOF nonlinear Generic Transport Model in a scenario with a broken left wing tip.
       
  • Dynamic analysis of functionally graded carbon nanotubes-reinforced plate
           and shell structures using a double directors finite shell element
    • Abstract: Publication date: July 2018Source: Aerospace Science and Technology, Volume 78Author(s): A. Frikha, S. Zghal, F. Dammak The present paper aims at the study of the dynamic behavior of functionally graded carbon nanotubes-reinforced composite shell structures (FG-CNTRC) via forced vibration analysis. The governing equations of motion are developed using a linear discrete double directors finite element model. The elaborated model is based on high-order-distribution of displacement field and uses a cubic variation of the vector position along the thickness direction. A zero transverse shear stress at top and bottom surfaces is also imposed. Four types of distributions of carbon nanotubes (CNTs) such that uniformly and three functionally graded distributions are considered. The extended rule of mixture is used to estimate the effective material properties of carbon nanotube-reinforced composite (CNTRC) shell. The applicability and the performance of the present model are illustrated by three numerical examples of FG-CNTRC square plates, spherical caps and annular ring plates. The transient center deflections of the studied shell structures are computed and depicted for different volume fractions and profiles of CNTs, various boundary conditions and other geometrical parameters in order to show the effect of these parameters on dynamic behavior of FG-CNTRC shells.
       
  • Numerical analysis of supersonic flows over an aft-ramped open-mode cavity
    • Abstract: Publication date: July 2018Source: Aerospace Science and Technology, Volume 78Author(s): Zhaoxin Ren, Bing Wang, Bowen Hu, Longxi Zheng The characteristics of supersonic cavity flows were investigated using large eddy simulation together with the acoustic analogy method. A fifth-order hybrid compact-weighted essentially non-oscillatory scheme was applied to calculate the convective flux, and a sixth-order compact scheme was used for the viscous flux. Farassat's Formula 1A was used to solve the Ffowcs William–Hawkings equations to obtain the far-field acoustic pressure fluctuations. The effects of cavity configuration and flow Mach number on the pressure waves generated by the interaction of shear vortices and cavity were compared. The ramped rear-step of the cavity can increase the more-organized level of flow coherent structures, and decrease the static pressure distribution on the cavity bottom-wall. The attenuation of the interactions between the shear layer vortex and the aft-ramped wall of the cavity can reduce the feedback of pressure waves upstream. The energy of the main frequency significantly decreases for the far-field acoustics in the upstream flow over the ramped rear-step cavity. Thus, the effectiveness of noise reduction by the rear-ramp is considerable for the area upstream of the cavity for the present conditions, but it is not the case opposite to and downstream of the cavity. The present conclusions are valuable for evaluating the performance of noise suppression by cavities embedded in supersonic inflows in engineering applications.
       
  • A novel ambiguity search algorithm for high accuracy differential GNSS
           relative positioning
    • Abstract: Publication date: July 2018Source: Aerospace Science and Technology, Volume 78Author(s): Yang Li It is well understood that the key to high accuracy differential global navigation satellite system (DGNSS) relative positioning is the resolution of the integer ambiguities within the carrier phase measurements and the continuous tracking of them. The resolution process is usually converted into an integer least square optimization problem, e.g., among them is the most notable Least-squares Ambiguity Decorrelation Adjustment (LAMBDA) algorithm. This paper adds additional statistical constraints to the existing LAMBDA approach to improve the performance of ambiguity resolution process when the LAMBDA ratio is below a certain predefined threshold. In order to fix the integer ambiguity as soon as possible, a novel ambiguity search algorithm is proposed, which is like the threshold based algorithm but explicitly exploits the correlation structure of the double difference covariance model and the measurement accuracy difference. To do that, the relationship between global navigation satellite system (GNSS) pseudorange measurement accuracy and the resolution of the integer ambiguity of carrier phase measurements is analyzed based on the GNSS distance measurement equations. Analytic statistical models of the single and double differences of the distance measurements are presented. Based on the analysis, it is found that the conventional choice of the highest elevation satellite as the reference satellite may not be a superior selection in single epoch algorithms. In fact, code phase measurements are used for ambiguity resolution, and the covariance of baseline vector is independent with reference satellite selection when the least square problem is optimally weighted. The novel ambiguity search algorithm is presented to fix the ambiguity as soon as possible. Simulation and field test data validate the analysis and the ambiguity search algorithm.
       
  • Fault detection and isolation of satellite gyroscopes using relative
           positions in formation flying
    • Abstract: Publication date: July 2018Source: Aerospace Science and Technology, Volume 78Author(s): Amir Shakouri, Nima Assadian A fault detection and isolation method for satellite rate gyros is proposed based on using the satellite-to-satellite measurements such as relative position beside orbit parameters of the primary satellite. By finding a constant of motion, it is shown that the dynamic states in a relative motion are restricted in such a way that the angular velocity vector of primary satellite lies on a quadratic surface. This constant of motion is then used to detect the gyroscope faults and estimate the corresponding scale factor or bias values of the rate gyros of the primary satellite. The proposed algorithm works even in time variant fault situations as well, and does not impose any additional subsystems to formation flying satellites. Monte-Carlo simulations are used to ensure that the algorithm retains its performance in the presence of uncertainties. In presence of only measurement noise, the isolation process performs well by selecting a proper threshold. However, the isolation performance degrades as the scale factor approaches unity or bias approaches zero. Finally, the effect of orbital perturbations on isolation process is investigated by including the effect of zonal harmonics as well as drag and without loss of generality, it is shown that the perturbation effects are negligible.
       
  • Modeling of incomplete combustion in a scramjet engine
    • Abstract: Publication date: July 2018Source: Aerospace Science and Technology, Volume 78Author(s): Jae Won Kim, Oh Joon Kwon In the present study, an empirical theoretical split chemistry model was developed to describe the phenomenon of incomplete combustion for scramjet engines. The model was developed by decoupling flow into two distinct regions, namely, unburned and burned, as in real scramjet flows. The conservation equations for the combustor and the rate equations for the supersonic nozzle were calculated independently for these two regions using the split ratio of the volume occupied by the fuel–air mixture to the overall volume. The split chemistry model was implemented in a one-dimensional flow solver by assuming that the combustion efficiency is known. The effect of incomplete combustion on the performance of a hydrocarbon-fueled scramjet engine was investigated by performing a parametric study along the entire flow path through the scramjet engine, including the inlet, isolator, combustor, and supersonic nozzle. The results showed that, for a combustion efficiency of 0.5 with a global equivalence ratio of 0.5, the overall temperature and the thrust performance along the flow path through the combustor and the nozzle significantly decrease owing to incomplete combustion. It was also observed that the chemical composition of the fuel-only region varies, regardless of the change in combustion efficiency, because efficiency is a function of the extent of the combustion reaction and the split ratio. It was found that the present split chemistry model is useful to describe incomplete combustion, and it can be effectively utilized for the preliminary design and analysis of scramjet engines.
       
  • Dual-polarized GPS antenna array algorithm to adaptively mitigate a large
           number of interference signals
    • Abstract: Publication date: July 2018Source: Aerospace Science and Technology, Volume 78Author(s): Kwansik Park, Dongkook Lee, Jiwon Seo Intentional or unintentional interference experienced by the Global Positioning System (GPS) is a significant concern for GPS-based critical infrastructures and services including aviation. An effective way to mitigate GPS interference is to utilize a GPS antenna array capable of electronically changing its gain pattern. Although a conventional GPS antenna array consists of single-polarized antenna elements, a dual-polarized antenna array has the potential to mitigate approximately twice the number of interference signals in the spatial domain as a single-polarized array because of the additional degrees of freedom provided. This paper proposes an adaptive beamforming algorithm using a dual-polarized GPS antenna array for mitigation of interference signals with various polarizations. In this paper, a dual-polarized antenna element specifically refers to two co-located crossed linearly polarized dipole antennas. The proposed minimum-variance-distortionless-response (MVDR)-based space–time adaptive processing (STAP) method utilizes a novel constraint vector that is specially designed for a dual-polarized GPS array. As the proposed constraint vector considers realistic radiation patterns of the antenna, the performance of the proposed method in terms of the signal-to-interference-plus-noise power ratio (SINR) is noticeably superior to that of previous methods under a representative interference scenario. The performance of the proposed method is compared with three previous methods utilizing dual-polarized antenna arrays.
       
  • Influences of anisotropic fiber-reinforced composite media properties on
           fundamental guided wave mode behavior: A Legendre polynomial approach
    • Abstract: Publication date: July 2018Source: Aerospace Science and Technology, Volume 78Author(s): Cherif Othmani, Anouar Njeh, Mohamed Hédi Ben Ghozlen The guided wave technique has been widely used for evaluating different structures. Recently, these acoustic waves have been implemented in non-destructive testing (NDT). Accordingly, these waves make up a set of motivated means for detecting defects because of their effectiveness for quickly testing a long series of specimens. On that account, the present article introduces a Legendre polynomial approach, for modeling guided dispersion curves solutions in anisotropic fiber-reinforced composite media. This polynomial approach offers a higher computational efficiency and simplicity in comparison to traditional methods. The validity of the proposed Legendre polynomial approach is illustrated by comparison with available data. The convergence of this method is discussed. Consequently, the computation time of the Legendre polynomial approach increases linearly when the number of truncation order M increases. In the same context, the computation time of this polynomial approach is compared to the ordinary differential equation (ODE) approach in terms of efficiency. In addition, the influence on the fundamental guided wave dispersion curves due to reductions in the material properties such as C11, C12, C13, C22, C23, C33, C44, C55, C66 and mass density were analyzed for anisotropic fiber-reinforced single-layered composite media with different propagation angles. The studies were performed by obtaining the behavior guided wave dispersion curves for each single-layered type. This was done by reducing the material properties mentioned above by 50% from the original value. Since the guided wave dispersion curves in a single-layered composite media varies with the propagation direction, the layers were analyzed at 0°, 45° and 90° propagation angles, with all the aforementioned variations. The computer programs in this work are written by using Matlab software.
       
  • Parametric study of supersonic film cooling in dual bell nozzle for an
           experimental air–kerosene engine
    • Abstract: Publication date: July 2018Source: Aerospace Science and Technology, Volume 78Author(s): Siba Prasad Choudhury, Abhilash Suryan, J.C. Pisharady, A. Jayashree, Khalid Rashid Numerical analysis is performed on a dual bell nozzle designed for an experimental semi-cryogenic rocket engine application to predict the effect of film injection on nozzle flow characteristics and transitional behavior. Both start-up and high-altitude operation regimes are simulated to predict actual flight conditions of a dual bell nozzle. Coolant is injected at two locations and at different operating conditions to study the effect of various parameters on flow behavior. Changes in shock interaction and shock patterns during startup flow with and without the injection of coolant are analyzed. An empirical relation for conventional nozzles has been applied to determine the transition pressure ratio. Actual transition flow from base to extension nozzle is found to be different from the calculated transition pressure ratio and flow transition occurs early in case of secondary injection. A large reduction in wall temperature is observed with the film flowing along the nozzle wall and it does not have any adverse effect on flow transition. Instead of efficiency, a film cooling effectiveness for high temperature flow is used to understand the effect of coolant temperature on reduction of heat flux and mixing characteristics. Mass flow rate of coolant is seen to have significant effect on mixing and flow separation.
       
  • Unsteady aerodynamic effects in landing operation of transport aircraft
           and controllability with fuzzy-logic dynamic inversion
    • Abstract: Publication date: July 2018Source: Aerospace Science and Technology, Volume 78Author(s): C. Edward Lan, Ray C. Chang Aircraft landing in strong wind has been a safety problem for all types of aircraft. The specific issues involve hard landing, roll oscillation and runway veer-off. These issues are related to atmospheric disturbances, and/or dynamic ground effect. As a result, the aerodynamics will be different from those in steady flow concept. In this paper, some of the pertinent stability and control derivatives based on a small-disturbance concept will be presented. How these local stability and control characteristics affect global controllability will be examined with Fuzzy-Logic Dynamic Inversion. Controllability is judged from whether necessary control deflections exceed the imposed limits. Specific examples involving a twin-jet transport with hard landing, rolling oscillation before touchdown and runway veer-off event due to varying crosswind after touchdown are illustrated.
       
  • Cable fracture simulation and experiment of a negative Gaussian curvature
           cable dome
    • Abstract: Publication date: July 2018Source: Aerospace Science and Technology, Volume 78Author(s): Jiamin Guo, Guangen Zhou, Dai Zhou, Weigang Chen, ZhiXin Xiong, Shilin Dong This paper describes a newly developed negative Gaussian cable-strut structure. It focuses on the fracture of a member using an experimental model and the corresponding vector form intrinsic finite element (VFIFE) model. First, this study considered the VFIFE algorithm for bars, cables, and beams. Next, an experimental model of a negative Gaussian curvature cable dome with its supporting system and the corresponding VFIFE model were built. Then, the given ridge cable was fractured using a shear force, and the structural dynamic response during fracture was tested. Finally, to further study the influence of fracture on the structure, different sections of three main ridge cables were selected, and their fractures were successively simulated using the VFIFE model. The results indicated that the VFIFE was an efficient and accurate way to simulate the member fracture of a negative Gaussian curvature cable dome. Furthermore, the results confirmed that members in a section with a negative curvature not only have a much greater effect on the structure but also are much more sensitive to member fracture.
       
  • Robust fault-tolerant controller design for aerodynamic load simulator
    • Abstract: Publication date: July 2018Source: Aerospace Science and Technology, Volume 78Author(s): Abdolah Shamisa, Zahra Kiani Load simulator is one of the main mechanisms for stability and performance evaluation of the rotational/translational actuators in the laboratory. The movement of (under testing) actuator generates a large disturbance on the load simulator known as “extraneous torque”. Elimination of this large surplus disturbance is the main concern of the dynamic load simulator design. The faults are unavoidable events in system operation. Sensor or actuator faults frequently occur in flight systems. The design method based on Quantitative Feedback Theory (QFT) can be used as a passive Fault-Tolerant Control (FTC) of the plants with sensor or actuator faults. In this paper, a QFT-FTC is proposed for the electric load simulator (ELS) in presence of sensor and actuator faults. For this purpose, a particular type of faults is used, which the sensor and actuator faults are considered as semi-deterministic jumps that occurring at random intervals with random amplitudes. In the first step, the faults are converted to parameter uncertainties and disturbance is transferred to the input and output of the plant. Then, a QFT controller is designed for this uncertain plant. Proposed QFT-FTC attenuates the large disturbance even if the control effort is limited. Under these circumstances, an adequate bandwidth is achieved. Furthermore, semi-deterministic jumping faults on sensor and actuator are applied during the simulations and high robust tracking performance is obtained in presence of the saturated control. Compared to H-infinity Controller, the proposed controller has a simpler structure and its tracking performance is better than H-infinity method.
       
  • Flow control mechanisms of a combined approach using blade slot and vortex
           generator in compressor cascade
    • Abstract: Publication date: July 2018Source: Aerospace Science and Technology, Volume 78Author(s): Jiaguo Hu, Rugen Wang, Danqin Huang Experiments proved the performance gains in a high-load cascade using a new combined flow control approach, but lack of clear explanations on flow interactions between the configurations and the cascade flow. A detailed discussion is conducted here to further reveal the flow control mechanisms based on experimental and numerical results. An overview of experimental studies is firstly presented to conclude the flow control benefits and to put forward the questions for the simulations. Cascade flow fields observed by experiments show that the combined approach works by two aspects: the slot produces high-speed jets to re-energize the suction side separated flows and reattach them to the suction surface; the vortex generator (VG) creates a counter-rotating vortex into cascade passage to further reduce the end-wall cross flows. Thus, both the two main sources of separations in cascade flow are considerably suppressed. The corner separation is suppressed by delaying the passage vortex (PV): The VG counter-balances and deflects the PV while the slot jet further limits its pitch-wise width. Coupling the effects of two devices, the cascade flow structure is improved and main vortices are significantly reduced in size and intensity, result in greater separation control effects than the individuals in the high-load cascade.
       
  • Method for simulating the performance of a boundary layer ingesting
           propulsion system at design and off-design
    • Abstract: Publication date: July 2018Source: Aerospace Science and Technology, Volume 78Author(s): C. Goldberg, D. Nalianda, D. MacManus, P. Pilidis, J. Felder Boundary layer ingestion has emerged as a potential propulsion concept on novel aircraft configurations for the future. As these concepts progress, preliminary design tools are required that enable the simulation of these aircraft and the rapid analysis of multiple configurations. Simulation tools for boundary layer ingesting propulsion systems tend to focus on proving performance benefits at design point. However, the simulation of aircraft configurations that utilise boundary layer ingestion requires a method to simulate the propulsion system at a range of flight conditions other than design point. A tool is therefore required to enable simulations at off-design. This research presents a work flow to simulate a boundary layer ingesting propulsion system at design and off-design. The process is intended as a tool for design space exploration and the rapid analysis of concepts at the conceptualisation phase. Boundary layer calculations have been combined with conventional 1-D gas turbine performance methods to predict performance of a propulsion system at design point. This method is then extended to enable simulations at off-design conditions for a range of flight conditions or propulsion system power settings. The formulation provides a thrust-drag representation that supports conventional aircraft simulation tools. A case study of an aircraft configuration which utilises an array of boundary layer ingesting propulsors is used to demonstrate the process. The performance of individual propulsors in the array is compared at off-design. Simulations found that, although each propulsor was sized for the same propulsive force at design point, off-design performance diverged depending on operating conditions. In addition, the performance of the propulsor array as a whole was predicted as a function of altitude and Mach number. The case study is used to draw general conclusions on the performance characteristics of a boundary layer ingesting propulsor.
       
  • Characteristics of unsteady total pressure distortion for a complex
           aero-engine intake duct
    • Abstract: Publication date: July 2018Source: Aerospace Science and Technology, Volume 78Author(s): Geoffrey Tanguy, David G. MacManus, Eric Garnier, Peter G. Martin Some types of aero-engine intake systems are susceptible to the generation of secondary flows with high levels of total pressure fluctuations. The resulting peak distortion events may exceed the tolerance level of a given engine, leading to handling problems or to compressor surge. Previous work used distortion descriptors for the assessment of intake-engine compatibility to characterise modestly curved intakes where most of the self-generated time-dependent distortion was typically found to be dominated by stochastic events. This work investigates the time-dependent total pressure distortion at the exit of two high off-set diffusing S-duct intakes with the aim of establishing whether this classical approach, or similar, could be applied in these instances. The assessment of joint probability maps for time dependent radial and circumferential distortion metrics demonstrated that local ring-based distortion descriptors are more appropriate to characterise peak events. Extreme Value Theory (EVT) was applied to predict the peak distortion levels that could occur for a test time beyond the experimental data set available. Systematic assessments of model sensitivities to the de-clustering frequency, the number of exceedances and sample time length were used to extend the EVT application to local distortion descriptors and to provide guidelines on its usage.
       
 
 
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