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Aerospace Science and Technology
Journal Prestige (SJR): 0.796
Citation Impact (citeScore): 3
Number of Followers: 341  
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1270-9638
Published by Elsevier Homepage  [3162 journals]
  • Optimal control based guidance law to control both impact time and impact
    • Abstract: Publication date: January 2019Source: Aerospace Science and Technology, Volume 84Author(s): Xiaotian Chen, Jinzhi Wang A new guidance law with both impact time and impact angle constraints is proposed in this paper. We first simplify missile dynamics under small heading error approximation, and derive an optimal guidance law with impact angle constraint against a stationary target. By adding a feedback controller to the obtained optimal guidance law, both impact time and angle requirements are achieved and the singularity problem is tackled. The proposed guidance law can be used to perform a simultaneous formation cooperative attack. Numerical simulations are demonstrated to illustrate the effectiveness of the proposed method.
  • A hybrid reduced-order modeling technique for nonlinear structural dynamic
    • Abstract: Publication date: Available online 10 November 2018Source: Aerospace Science and TechnologyAuthor(s): Chen Yang, Ke Liang, Yufei Rong, Qin Sun Thin-walled structures are always subjected to a large range of extreme loading cases leading to obvious geometric nonlinearities in structural dynamic response, such as vibration with large amplitudes in aeronautics and astronautics field. Various dynamic reduced-order models have been investigated from detailed finite element models, to largely reduce the computational burden of the structural dynamic responses. However, to construct these low-order models,applying a series of nonlinear static simulations to the full-order model is necessary. This paper aims to develop a hybrid reduced-order modeling method by combining the dynamic and static reduced-order models together, to estimate the dynamic transient response caused by geometrically nonlinear finite element models. A few free-vibration modes of interest are selected to reduce basis vectors of dynamic reduced-order model. Based on Koiter asymptotic expansion theory, the constructed static reduced-order model is applied to the nonlinear static analyses. Therefore, not only does the proposed method make it possible to calculate the nonlinear dynamic response far more efficiently than full-order modeling methods, but computational burdens in construction of dynamic reduced-order model are also largely reduced compared to existing approaches. Various engineering numerical examples with hardening and/or softening nonlinearities are carefully tested to validate the good quality and efficiency of the proposed method.
  • Large-eddy simulation of shock-wave/boundary-layer interaction control
           using a backward facing step
    • Abstract: Publication date: Available online 9 November 2018Source: Aerospace Science and TechnologyAuthor(s): Weipeng Li, Hong Liu A new passive flow control method, putting a backward facing step ahead of the shock interaction position, is numerically investigated, aiming to control the shock-wave/boundary-layer interaction in a rocket-based combined-cycle scramjet engine. The height of the step is designed to be smaller than the boundary layer thickness. Implicit large-eddy simulations of an oblique shock wave impinging on a supersonic turbulent boundary layer are performed to examine the efficiency of this flow control method. Results show that with the flow control the length of shock-induced separation bubble is increased, but its height is reduced. The upstream extending of the reflected shock is suppressed, which indicates that the flow control method is able to relieve or avoid the adverse effects caused by the inner going of the reflected shock into the air-intake of the engine. The mechanism and the influence of the applied control method on instantaneous, mean and statistical flow-fields are discussed.
  • Numerical investigation of the effects of different parameters on the
           thrust performance of three dimensional flapping wings
    • Abstract: Publication date: January 2019Source: Aerospace Science and Technology, Volume 84Author(s): Chunlin Gong, Jiakun Han, Zongjing Yuan, Zhe Fang, Gang Chen After billions of years of evolution, many creatures employing flapping wing in nature tend to have excellent flight capabilities. To understand the bionic wings flow mechanism will be helpful to design high performance underwater vehicles and new conception aircrafts. The geometric parameters, kinematic parameters and flow parameters have great effects on the bionic wings thrust performance. Facing the diverse parameters, it's very difficult to explore the three-dimensional (3D) bionic flapping wing flow mechanism with traditional numerical simulation method. In this paper, a general large-scale parallel solver using Immersed Boundary-Lattice Boltzmann Method (IB-LBM) was developed. The evolution procedures of the 3D flapping wing leading edge vortex and wake flow vortex structures were analyzed in detail. Our study explained the 3D flapping wing thrust performance variation with different wing shapes, aspect ratios and pitch-bias angles of attack. Using Chinese supercomputer TianHe-II presents a wide range of possibilities for the further development of parallel IB-LBM, employing tens of millions grids will help us to obtain more complete and accurate 3D flapping wing flow field information. It's indicated that the obtuse wing has the best thrust performance compared with other sharp wing shapes. With the increase of the aspect ratio, the thrust coefficient of flapping wing increases firstly and then decreases, and with pitch-bias angles of attack increases, the thrust coefficient decreases quickly or even shown resistance phenomenon at the large pitch-bias angel of attack. The discussion of these parameters will provide a theoretical basis for improving flapping-like vehicles propulsive performance.
  • Time-optimal trajectory generation for aerial coverage of urban building
    • Abstract: Publication date: January 2019Source: Aerospace Science and Technology, Volume 84Author(s): Peng Yao, Yangguang Cai, Qian Zhu This paper presents a hierarchical architecture for generating the cooperative trajectories of multiple unmanned aerial vehicles (UAVs) attached with camera sensors, which aim to cover buildings with optimal time in 3D urban environment. It incorporates the centralized high-level layer performing the mission analysis and task allocation functions yielding instructions that are transmitted to the UAVs, as well as the decentralized low-level fashion that the UAVs perform the trajectory generation function in turn. First, the mission features especially the theoretical coverage time of building envelope are extracted quantitatively, and the buildings are then allocated to the UAVs in order to convert the cooperative control problem into multiple single-vehicle control problems. Then, each UAV visits and scans its allocated buildings sequentially, and the corresponding coverage trajectories are obtained by the parallel circle strategy (PCS) and the time-optimal guidance vector field (TOGVF) transition method, as well as the interfered fluid dynamic system (IFDS) method for obstacle avoidance. Finally, our proposed method is verified in various scenarios, and the simulation results show its high efficiency with least time to solve the cooperative coverage problem.
  • Surrogate model of complex non-linear data for preliminary nacelle design
    • Abstract: Publication date: January 2019Source: Aerospace Science and Technology, Volume 84Author(s): Alexander Heidebrecht, David G. MacManus Most response surface methods typically work on isotropically sampled data to predict a single variable and fitted with the aim of minimizing overall error. This study develops a metamodel for application in preliminary design of aircraft engine nacelles which is fitted to full-factorial data on two of the eight independent variables, and a Latin hypercube sampling on the other six. The specific set of accuracy requirements for the key nacelle aerodynamic performance metrics demand faithful reproduction of parts of the data to allow accurate prediction of gradients of the dependent variable, but permit less accuracy on other parts. The model is used to predict not just the independent variable but also its derivatives, and the Mach number, an independent variable, at which a certain condition is met. A simple Gaussian process model is shown to be unsuitable for this task. The new response surface method meets the requirements by normalizing the input data to exploit self-similarities in the data. It then decomposes the input data to interpolate orthogonal aerodynamic properties of nacelles independently of each other, and uses a set of filters and transformations to focus accuracy on predictions at relevant operating conditions. The new method meets all the requirements and presents a marked improvement over published preliminary nacelle design methods.
  • Numerical analysis of transonic buffet flow around a hammerhead payload
    • Abstract: Publication date: Available online 7 November 2018Source: Aerospace Science and TechnologyAuthor(s): Yi Liu, Gang Wang, Hongyu Zhu, Zhengyin Ye During ascent of launcher, the unsteady aerodynamic loads associated with transonic buffet flow have become of considerable concern. To study the unsteady dynamics of buffet flow, delayed detached-eddy simulations of a hammerhead configuration have been conducted at transonic Mach numbers. The results, including mean Cp, Cprms, PSD and Schlieren visualizations, were validated by the measurements obtained from the wind-tunnel experiments. Nevertheless, to perform a good validation for unsteady loads, the numerical data needed to be filtered according to the data acquisition used in the experiments. The studies were performed by means of instantaneous, statistical, spectral and cross-spectral analysis of the numerical data, which identify the fluid dynamic mechanism that produces a relatively strong buffet environment. The mechanism involves a sequence of vortex, which is shed downstream, merges together, and ultimately impinges on the wall leading to large fluctuations. Besides, the cross-spectral analysis also revealed that the subsequent large scale and low frequency vortex shedding of the developed shear layer provides a strong influence on the flows around cone-cylinder conjunction. The fluctuations in this area are highly sensitive to Mach numbers, and the peak of Cprms appears at Ma ≈ 0.81.
  • A spline ROM of blade aerodynamic force to upstream wake
    • Abstract: Publication date: Available online 7 November 2018Source: Aerospace Science and TechnologyAuthor(s): Li Li-zhou, Yang Minglei, Luo Xiao, Zhang Jun, Yuan Mei-ni All related research nowadays are devoted to build ROM of aerodynamic forces induced by vibration of blades or wings. There is no discussion of ROMs of the aerodynamic forces of the blades corresponding to upstream wakes, which is more important to turbine machines' safety. In this paper, a spline Volterra ROM method is proposed to predict the blades' aerodynamic forces induced by the upstream wakes to fasten the blade-wake interaction analysis in turbine machine design. Traveling wave method is applied to simplify the inputs representing the upstream wakes. The kernels of the Volterra ROM are expressed in spline to reduce the number of parameters to be identified. The coefficients of the spline kernels are identified by minimizing the difference between ROM results and CFD data. The ROM method is used to predict a blade's aerodynamic forces under an actual wake. The results show that the ROM can capture most information of the aerodynamic forces due to the wake.
  • Solution-Based Adaptive Mesh Redistribution Applied to Harmonic Balance
    • Abstract: Publication date: Available online 7 November 2018Source: Aerospace Science and TechnologyAuthor(s): Reza Djeddi, Kivanc Ekici A primary source of inaccuracy in numerical simulations is due to errors that are introduced into the solution via the discretization of the continuous governing equations over the computational domain. By increasing the grid resolution in regions with high flow gradients and large curvatures using a solution-adaptive approach, these discretization errors can be reduced. In this paper, an adaptive mesh technique is presented that can efficiently cluster the grid nodes in sensitive regions by redistribution and relocation of the grid nodes. This adaptive technique is specifically important to unsteady periodic flow cases where the length scales of the flow features (such as shocks, boundary layer, and separation zones) can differ between time instances. The proposed technique is developed – for the first time in the literature – for a harmonic balance method to efficiently model unsteady periodic flows. To study the performance of the proposed technique in improving the accuracy of the flow solver, steady and unsteady flow cases are studied. Numerical results show that the adaptive mesh redistribution technique is capable of efficiently increasing the accuracy of the numerical solver with a relatively low computational overhead.
  • Skin Friction Drag Reduction over Staggered Three Dimensional Cavities
    • Abstract: Publication date: Available online 6 November 2018Source: Aerospace Science and TechnologyAuthor(s): Erwin R. Gowree, Chetan Jagadeesh, Christopher J. Atkin The effect of three-dimensional staggered circular cavities on a zero-pressure gradient incompressible turbulent boundary layer was studied. Two key parameters were varied, being the ratio of the diameter, d, to the depth, h, of the cavity, d/h and the Reynolds number based on the diameter of the cavity, Rd. Velocity profile measurements showed that for the cases of d/h>1 an increase in skin friction drag was experienced with respect to a smooth surface, but for d/h≤1 the drag increment was almost negligible and in some cases it was lower than that of a smooth surface by up to 10%. Measurements along the spanwise plane showed the presence of organised transverse velocity components which bear some resemblance with the flow over riblets. The skin friction drag appears to be a strong function of Rd, where for Rd>5500 a drag increment is experienced which could potentially be due to shear layer breakdown and more production of turbulence.
  • Parametric study of a VLS based on 2-D FSI analysis
    • Abstract: Publication date: Available online 6 November 2018Source: Aerospace Science and TechnologyAuthor(s): HyunShig Joo, Haeseong Cho, Younghun Lee, SangJoon Shin, Jack J. Yoh, Jae-Cheol Shin Vertical launching system(VLS) is useful in operating and sheltering high-speed rockets. The aft closure in the plenum plays a significant role in protecting the interiors from the exhaust gas induced by the ignition of adjacent or in-positioned canisters. During the aft opening/closing event, a complex flow is propagated into the VLS . By presence of such structural components, it is necessary to analyze the interaction between the deforming aft closure and a highly pressurized plume.This paper presents a two-dimensional fluid-structure interaction(FSI) simulation under high pressure loading condition for preliminary design of VLS. A quadrilateral 9-node element based on co-rotational (CR) framework is used to predict the geometrically/materially nonlinear deformation of the aft closure while supersonic impinging jet plume is predicted by fully Eulerian modeling. A contact mechanism is also utilized to apply reaction forces between the structures and inclined plenum using a penalty term. The interface and boundary conditions are obtained by the hybrid particle level-set method via the Ghost framework. Furthermore, a parametric study is conducted by changing the thickness of the aft closure and the inclined angle of the plenum. It is expected that the magnitudes of pressure and temperature can be decreased by the introduction of appropriate thickness of the aft closure and inclined angle in the plenum.
  • Barrier Lyapunov function-based robust flight control for the ultra-low
           altitude airdrop under airflow disturbances
    • Abstract: Publication date: January 2019Source: Aerospace Science and Technology, Volume 84Author(s): Zikang Su, Chuntao Li, Honglun Wang This paper investigates the anti-disturbance constrained trajectory flight control for the ultra-low altitude airdrop under airflow disturbances, by innovatively integrating the finite time convergent high-order sliding mode observer and barrier Lyapunov function-based back-stepping technique. The dynamics of transport aircraft during the airdrop are established based on the fixed-wing aircraft's 6 DOF nonlinear model and are transformed into the affine nonlinear form for the convenient control design. These dynamics include the complex influence of the flow disturbances, the ground effect, the consecutive movement and abrupt extraction of the heavy cargo. Then, the flight controller is divided into several cascade subsystems via back-stepping technique. The items reflect the disturbances during the drop in each subsystem, as well as the items which are independent of the predefined virtual control variables, are taken as components of the “lumped disturbances” which are estimated and compensated by the specially designed finite time convergent high order sliding mode observer. On this basis, a barrier Lyapunov function-based back-stepping flight controller is proposed for the robust and safe flight control of the ultra-low altitude airdrop. And the closed-loop stability is discussed via the Lyapunov stability theorem. Simulation comparisons are conducted to verify the robustness and effectiveness of the proposed airdrop flight control method.
  • Model reference adaptive state-dependent Riccati equation control of
           nonlinear uncertain systems: Regulation and tracking of free-floating
           space manipulators
    • Abstract: Publication date: January 2019Source: Aerospace Science and Technology, Volume 84Author(s): Saeed Rafee Nekoo This work proposes a model reference adaptive state-dependent Riccati equation (SDRE) controller for nonlinear time-invariant systems considering uncertainty in the plant. The SDRE is vulnerable to uncertainty of nonlinear model, hence the adaptive structure is to compensate for the difference between a reference model and a real uncertain system. The application of the proposed method is dedicated to controlling a free-floating space manipulator (FFSM), a robotics system with a base in two modes: an inactive (no actuation or thrust) state, and a base reaction torque mode. A non-actuated heavy base FFSM probably performs a regulation or a tracking task precisely though that might not be a good solution. A new design is proposed for FFSM control: a heavy base is selected for base of a reference model and the uncertain system with proper weight of base will follow the reference system; and considering three motors for rotating back the base when it reorients from initial position. The new design has improved the precision of the FFSM and reduced the weight of the robot. A planar two degree-of-freedom and a 3D Stanford arm were modeled, simulated and analyzed to assess the performance of the proposed structure and adaptive SDRE controller; that successfully confirmed the claimed expectations.
  • Adaptive super-twisting sliding mode control of 6-DOF nonlinear and
           uncertain air vehicle
    • Abstract: Publication date: January 2019Source: Aerospace Science and Technology, Volume 84Author(s): Ali-Reza Babaei, Maryam Malekzadeh, Davood Madhkhan In this paper, to control the six degree-of-freedom non-linear unmanned aerial vehicle, two strategies are implemented using adaptive super-twisting sliding mode control approach. The first one is a single-channel controller that is designed on the basis of decoupled equations of motion. The other one is a three-channel controller that is designed based on the coupling equations of motion along with an adaptive super-twisting observer. The stability of the closed loop system of the controller-observer is proven. The comparison between the single-channel controller and the three-channel could lead us to select between a little lower efficiency and less complexity versus efficiency and more complexity. To examine the performance and robustness of these two control loops, their performances are analyzed in the presence of combined uncertainties, including aerodynamics, mass, inertial moment, sensor, and actuator disturbances and parametric uncertainties in the stage separation phase. The explosive bolt separation mechanism is assumed to perform the stage separation, and its forces, moments and disturbances are modeled as needed. Finally, the responses are compared with the classic PID controller.
  • Characteristics of entropy layer for cones and cylinders in supersonic
    • Abstract: Publication date: Available online 5 November 2018Source: Aerospace Science and TechnologyAuthor(s): Wang Gang, Zhang Wen-xi, Xie Zhu-xuan, Yang Yan-guang An analytic method is presented to study the distribution of vorticity downstream the shock wave and the characteristics of the entropy layer for various cones and cylinders in supersonic flows. The relations of shock-shape, the distribution character of various parameters within the shock layer, and the entropy increment were combined to obtain the characteristics of vorticity and the entropy gradient. Numerical simulation are performed at the Mach number of 3, 5 and 10. The results indicate that the distribution of entropy and vorticity is connected with shock shape directly. Due to the differences of the shape of shock, the vorticity and the extreme value of entropy gradient for blunt-nosed cylinders are both larger than the cases for flat cylinders. As the shock-shape of flat-nosed cylinders is more liable to be affected than blunt-nosed cylinders with increasing Mach number, the position of the extreme value moves to the surface as the Mach number increases for flat-nosed cylinders, while it remains the identical value for blunt-nosed cylinders. The vorticity is regarded as the criterion of the edge of entropy layer in the normal direction, and two methods are proposed and discussed to estimate the edge.
  • Near time-optimal controller based on analytical trajectory planning
           algorithm for satellite attitude maneuver
    • Abstract: Publication date: Available online 5 November 2018Source: Aerospace Science and TechnologyAuthor(s): Li You, Ye Dong Near time-optimal controller based on analytical trajectory planning algorithm for satellite attitude maneuver is proposed in this paper. The attitude maneuver issue is constructed as three successive attitude maneuvers and the desired trajectory is derived by calculating the minimum rotate angle, meanwhile each maneuver process is optimized by Bang-Bang control logic so that the system could have near time optimal character. The constraint on control torque is discussed and the relationship between system upper bound and control parameters is given. A special case of attitude maneuver is discussed and system acceleration and deceleration process is optimized inspired by Hohmann transfer of orbit control. The analytical solution of desired trajectory is given hence the computation is largely reduced. The attitude tracking controller is designed so that system could maneuver along the designed trajectory. System stability is proved by Lyapunov method and system performance is demonstrated by numerical simulation.
  • Principles of non-intrusive diagnostic techniques and their applications
           for fundamental studies of combustion instabilities in gas turbine
           combustors: A brief review
    • Abstract: Publication date: Available online 3 November 2018Source: Aerospace Science and TechnologyAuthor(s): Can Ruan, Feier Chen, Weiwei Cai, Yong Qian, Liang Yu, Xingcai Lu Combustion instabilities are often manifested in modern fuel-lean gas turbine combustors. Investigating the mechanisms and developing control strategies for combustion instabilities in such systems are of practical importance and give rise to interesting scientific issues as large-amplitude pressure and heat release perturbations can lead to catastrophic and irreversible consequences on costly gas turbine hardware. In recent years, tremendous efforts have been made to achieve a deeper understanding of the periodic combustion oscillations in gas turbine engines with both advanced numerical simulations and experimental diagnostics. In the latter case, state-of-the-art, non-intrusive diagnostic techniques have been well adopted to conduct fundamental studies on combustion instabilities in gas turbine model combustors. For example, simultaneous time-resolved measurements with planar laser-induced fluorescence (PLIF) for characterizing flame structure and particle image velocimetry (PIV) for imaging flow field significantly contribute to the understanding of the role of flame-flow-acoustics coupling in the events of combustion instabilities, and to the development and validation of advanced numerical models. However, planar measurements can be restrictive when flames are not axisymmetric or exhibit complex large-scale three-dimensional (3D) dynamics, which are commonly encountered in practical combustion system when combustion instabilities occur. Therefore, more recently, new volumetric imaging techniques for combustion diagnostics have attracted considerable research efforts. This paper categorizes different advanced non-intrusive combustion diagnostic techniques, including their basic principles and especially applications for the study of combustion instability. Some of the recent progresses in the diagnostic techniques, such as computed tomography of chemiluminescence (CTC), volumetric laser induced fluorescence (VLIF), rainbow-PIV, etc., are also discussed. These volumetric combustion diagnostic techniques offer the advantage to measure both spatial and temporal characteristics of the flame/flow of interest, which will enable deeper insights into the nature of unsteady combustion in the future. This brief review is intended to be useful for both researchers and engineers to design and conduct further fundamental experiments on combustion instabilities in gas turbine engines.
  • Aerodynamic design of multi-propeller/wing integration at low Reynolds
    • Abstract: Publication date: January 2019Source: Aerospace Science and Technology, Volume 84Author(s): Kelei Wang, Zhou Zhou, Xiaoping Zhu, Xiaoping Xu Based on the detailed flow characteristics analyses of a base four-propeller/wing integration at a low Reynolds number of 3.0×105, new multi-propeller/wing integrated aerodynamic design philosophy and methodology have been developed and validated numerically. The core of the present design philosophy is to make good use of coupling effects between two adjacent propellers to realize the low-Reynolds-number flow-field reconstruction, thus to improve the aerodynamic performance of the multi-propeller/wing integration at the operating power-on state. The multi-reference frame (MRF) technique which quasi-steadily solves the Reynolds-averaged Navier–Stokes (RANS) equations coupled with transition model is used to design the example four-propeller/wing integration at a low Reynolds number of 3.0×105. As a result, the designed multi-propeller/wing integration yields a maximum lift-to-drag ratio of 72.81, which represents a 21.08% increase compared to the base four-propeller/wing integration.
  • Fixed-time autonomous shipboard landing control of a helicopter with
           external disturbances
    • Abstract: Publication date: January 2019Source: Aerospace Science and Technology, Volume 84Author(s): Yanting Huang, Ming Zhu, Zewei Zheng, Mir Feroskhan This paper presents a new fixed-time control algorithm to enable autonomous landing of a helicopter onto the ship's deck in the presence of parametric uncertainties and external disturbances. A nonsingular terminal sliding control is implemented as an integral part of the fixed-time control scheme, that guarantees the convergence of system errors to zero in a fixed settling time, however, without the consideration of disturbances. Subsequently, a fixed-time disturbance observer is incorporated into the control structure to efficiently estimate the lumped disturbances including modeling inaccuracies and external perturbations, while reducing the undesired chattering in the control inputs effectively as well. By establishing a relative motion model between the helicopter and the ship, the shipboard landing problem is converted from a general trajectory tracking problem to a more favorable stabilization problem. Based on the fixed-time control scheme in the relative motion model, a relative position controller (RPC) and a relative attitude-altitude controller (RAC) are formulated to guide the helicopter in a dual-phase landing sequence. The RPC will first be implemented to direct the helicopter from its initial position to a hover position above the ship. The next phase involves the application of RAC to guide the helicopter to descend steadily on the ship. Numerical comparative simulations are also carried out to validate the remarkable performance of the proposed control approach.
  • Modeling and vibration control of aero two-blade propeller with input
           magnitude and rate saturations
    • Abstract: Publication date: Available online 30 October 2018Source: Aerospace Science and TechnologyAuthor(s): Xueyan Xing, Jinkun Liu, Lijun Wang In this paper, the dynamic modeling and vibration control of a two-blade propeller system of an aircraft are investigated in the presence of input magnitude and rate constraints and external disturbances. To avoid discretizing the original system, a partial differential equation (PDE) model preserving all system modes is developed. Based on the proposed PDE model, boundary control laws are derived to restrict the bending and twist deformations of the two-blade propeller under disturbances. To meet the input magnitude and rate constraints, a backstepping controller is designed. The closed-loop system stability is proved by using the Lyapunov's direct method. Numerical simulations are presented to demonstrate the effectiveness of the proposed control method.
  • Comparison of Filtering Techniques For Relative Attitude Estimation of
           Uncooperative Space Objects
    • Abstract: Publication date: Available online 29 October 2018Source: Aerospace Science and TechnologyAuthor(s): Vincenzo Pesce, Muhammad Farooq Haydar, Michèle Lavagna, Marco Lovera Nowadays, one of the most active research fields in space engineering is autonomous relative navigation around uncooperative objects. A common approach used to tackle this problem is through vision-based pose determination techniques. This paper investigates the possibility of using non-linear filtering techniques to improve the attitude estimation performance of vision-based methods. Furthermore, a simulation study is presented to compare the proposed nonlinear techniques with the multiplicative extended Kalman filter for attitude estimation. First-order and second-order nonlinear filters are adapted, implemented and tested for relative attitude estimation. Finally, the consequences of uncertainty in the knowledge of the target inertia matrix are investigated.
  • The efficiency of a pulsed detonation combustor–axial turbine
    • Abstract: Publication date: November 2018Source: Aerospace Science and Technology, Volumes 82–83Author(s): Carlos Xisto, Olivier Petit, Tomas Grönstedt, Andrew Rolt, Anders Lundbladh, Guillermo Paniagua The paper presents a detailed numerical investigation of a pulsed detonation combustor (PDC) coupled with a transonic axial turbine stage. The time-resolved numerical analysis includes detailed chemistry to replicate detonation combustion in a stoichiometric hydrogen–air mixture, and it is fully coupled with the turbine stage flow simulation. The PDC–turbine performance and flow variations are analyzed for different power input conditions, by varying the system purge fraction. Such analysis allows for the establishment of cycle averaged performance data and also to identify key unsteady gas dynamic interactions occurring in the system. The results obtained allow for a better insight on the source and effect of different loss mechanisms occurring in the coupled PDC–turbine system. One key aspect arises from the interaction between the non-stationary PDC outflow and the constant rotor blade speed. Such interaction results in pronounced variations of rotor incidence angle, penalizing the turbine efficiency and capability of generating a quasi-steady shaft torque.
  • The trailing vortices generated by a reverse delta wing with different
           wing configurations
    • Abstract: Publication date: November 2018Source: Aerospace Science and Technology, Volumes 82–83Author(s): T. Lee, S.M. He The effects of cropping, anhedral, Gurney flaplike strips and winglets on the vortex flow and aerodynamic properties of a reverse delta wing (RDW) were investigated at Re = 3.81 × 105. The cropping led to a minor change in the RDW vortex flow property and aerodynamics while the anhedral produced inferior aerodynamics but strengthened vortices compared to the baseline wing. The Gurney flaplike strips increased both the lift and drag and vortex strength. Meanwhile, the winglets kept the vortex flow properties mainly unchanged. The lift force predicted based on the vortex strength was found to be within 4% to 14% difference compared to the force balance data, which suggests that although the outboard location of the RDW trailing vortices appeared to imply their irrelevance to the lift production, their strength, however, represented a significant portion of the lift. Finally, the lift-induced drag computed based on the vorticity flowfield was also found to account for 17–27% of the total drag. The present measurements will serve as a comparison for next-phase ground effect study.
  • Dispersion curves for a natural fibre composite panel: Experimental and
           numerical investigation
    • Abstract: Publication date: November 2018Source: Aerospace Science and Technology, Volumes 82–83Author(s): Giuseppe Petrone The design of orthotropic panels, in which some mechanical properties are associated to high degrees of uncertainty, such as for the natural fibres, is very arduous and often techniques that give local information are needed. In this paper a unidirectional flax–polyethylene panel is experimentally and numerically investigated. Experimentally, for a given distance source–receiver, the group velocities are obtained by processing the guided waves time-transient signals via a time-frequency transform leading to an estimation of the dispersion curves for different fibre directions and frequencies. Test results are then compared and used to validate numerical ones, obtained by means of both Finite Element and Wave Finite Element models.
  • Experimental study on the accretion and release of ice in aviation jet
    • Abstract: Publication date: November 2018Source: Aerospace Science and Technology, Volumes 82–83Author(s): Mathias Schmitz, Gerhard Schmitz Ice formations in aircraft fuel systems pose a serious safety threat with potentially disastrous consequences, when restricting the fuel flow towards the engines. This is an ongoing challenge in the aerospace industry. In this work experimental studies have been performed to investigate the effects of temperature, flow rate and surface properties on the accretion and release of ice in flowing fuel. A test rig with a glass-windowed pipe has been employed to quantitatively measure the transient icing process under controlled conditions. The accreted ice exhibited soft and fluffy characteristics and was most likely the result of impinging solid ice particles that were entrained in the fuel flow. The ice particles were most sticky in a temperature range between −6°C and −20°C. The thickness of accreted ice decreased with roughness on aluminium surfaces and there was a significant reduction on polytetrafluoroethylene (PTFE) and polymethyl methacrylate (PMMA) in comparison to aluminium, copper or stainless steel surfaces. Comparison of the thickness of accreted ice with the ice adhesion strength reported in the literature showed a clear correlation. The experimental results will help to gain better understanding of the ice accretion process in flowing fuel and may serve as basis for design guidelines to minimize ice formation within an aircraft fuel system.
  • Multidisciplinary optimisation of bipropellant rocket engines using H2O2
           as oxidiser
    • Abstract: Publication date: November 2018Source: Aerospace Science and Technology, Volumes 82–83Author(s): Adam Okninski, Jan Kindracki, Piotr Wolanski Today's rocket chemical propulsion systems for in-orbit use rely on toxic liquid rocket propellants. The need for environmentally-friendly spacecraft and upper-stage high-performance engines can be seen. This paper covers the topic of optimisation of Geostationary Transfer Orbit apogee bipropellant rocket engines, using highly concentrated hydrogen peroxide as oxidiser and kerosene as fuel. Performance, structural and heat transfer analyses are described. In particular a detailed mass model for hydrogen peroxide/kerosene rocket propulsion systems is discussed. Special care is given to bipropellant rocket systems using staged combustion configurations where a catalyst bed is utilised. The optimisation process was conducted using Matlab software. The ultimate goal of this work was the development of a tool for hydrogen peroxide/hydrocarbon bipropellant rocket propulsion system optimisation in terms of given requirements and design constraints. The presented software may enable the development of advanced, environmentally-friendly satellites and highly-efficient architectures utilising storable green propellants, including small upper-stage propulsion systems.
  • Aerodynamic characterization of a transonic axial flow compressor stage
           – with asymmetric tip clearance effects
    • Abstract: Publication date: November 2018Source: Aerospace Science and Technology, Volumes 82–83Author(s): S. Satish Kumar, Dilipkumar Bhanudasji Alone, Shobhavathy M. Thimmaiah, Janaki Rami Reddy Mudipalli, Ranjan Ganguli, S.B. Kandagal, Soumendu Jana This manuscript discusses the performance of a single-stage transonic axial flow compressor with non-uniform/asymmetric rotor tip clearance. Detailed steady and unsteady experimental measurements are carried out for a compressor with non-uniform clearance over the rotor. Measurements are focused at the peak clearance region of the compressor annulus where stall inception is likely to occur. A sector-based steady-state CFD simulation is performed on the compressor stage with uniform averaged rotor running clearance obtained from the blade growth estimates at design speed using structural analysis. The role of the tip leakage vortex on the stall dynamics of the compressor is elucidated. The stall events/disturbances occurring at every two rotor revolutions are shown using hotwire measurements. Varied flow features of the transonic compressor stage are discussed for different compressor speeds investigated. The level of clearance eccentricity/asymmetry existing in this compressor due to its complex spread does not degrade the overall compressor performance behavior.
  • Disturbance observer-based finite-time attitude maneuver control for micro
           satellite under actuator deviation fault
    • Abstract: Publication date: November 2018Source: Aerospace Science and Technology, Volumes 82–83Author(s): Jianzhong Qiao, Dafa Zhang, Yukai Zhu, Peixi Zhang Precise and fast attitude maneuvers are a requirement in many future space missions. However, the actuator deviation fault of micro satellite is inevitable, which affects the precision of spacecraft pointing. To overcome this difficulty, this paper presents a novel attitude control scheme to compensate the actuator deviation fault and achieve the finite-time attitude maneuver. Moreover, the proposed control scheme is constituted by an outer attitude tracking loop and an inner angular velocity tracking loop according to dynamic features of micro satellite. In the outer loop, a novel virtual control law, namely a desired angular velocity command, is developed, under which the finite-time attitude tracking can be achieved. Furthermore, in the inner loop, an effective composite controller which consists of a terminal sliding mode controller and a finite-time disturbance observer (FTDO) is proposed. The aim of composite controller is to ensure that the angular velocity can track the virtual control law in finite time, where the FTDO is designed to estimate and compensate the actuator deviation fault in the feed-forward channel. Finally, simulation results are conducted to demonstrate the effectiveness of the proposed control scheme.
  • Multi-phase smoothed particle hydrodynamics modeling of supercooled large
           droplet dynamics for in-flight icing conditions
    • Abstract: Publication date: November 2018Source: Aerospace Science and Technology, Volumes 82–83Author(s): Vahid Abdollahi, Wagdi G. Habashi, Marco Fossati Understanding the dynamics of a single large water droplet is needed for accurate simulations of the in-flight icing phenomenon. Obtaining information on the ratio of ejected to deposited water and the post-impact droplet distribution should improve the numerical modeling of the bulk of impinging droplets. In this study, a weakly compressible multi-phase Smoothed Particle Hydrodynamics (SPH) method with shifting algorithm and surface tension model is presented to simulate the single droplet dynamics. The validity of the approach has been proved by modeling the classical problems of Rayleigh–Taylor instability, dam break, and droplet formation by comparing against other numerical and experimental data in the literature. Finally, droplet impingement on a liquid film and dry solid surface has been simulated and compared against the experimental data. The effect of impact angle and film thickness on the crown formation is studied to demonstrate the importance of modeling SLD impingement for in-flight icing conditions.
  • Adaptive fault-tolerant cooperative guidance law for simultaneous arrival
    • Abstract: Publication date: November 2018Source: Aerospace Science and Technology, Volumes 82–83Author(s): Guofei Li, Yunjie Wu, Pengya Xu The problem of simultaneous arrival is investigated in this paper for multiple interceptors under partial actuator effectiveness. A fault-tolerant cooperative guidance is presented, in which an adaptive law is designed for disposing of the uncertainty. The convergence analysis demonstrates that the simultaneous arrival could be achieved in fixed-time interval under the actuation failures. The upper bound of convergence time is not dependent on the initial conditions of interceptors. The simulation results validate the effectiveness of proposed cooperative guidance law satisfactorily.
  • Computational aerodynamics analysis of a light sport aircraft: Compliance
           study for stall speed and longitudinal stability certification
    • Abstract: Publication date: November 2018Source: Aerospace Science and Technology, Volumes 82–83Author(s): S. Piedra, E. Martinez, C.A. Escalante-Velazquez, S.M.A. Jimenez The present work reports an aerodynamics analysis conducted to analyze the compliance of flight requirements of a new light sport aircraft (LSA) design in accordance with the ASTM F2245 and COAV-27/12. This new design is termed Halcon II and is property of the Horizontec aircraft company. At the conceptual design stage, vortex lattice method (VLM) calculations are implemented to compute the polar curves of the isolated wing and the complete aircraft. After the conceptual design of the aerodynamic surfaces is almost completed, the computational fluid dynamics simulations (CFD) are implemented in OpenFoam to characterize the flow around the aircraft. The CFD simulations consider steady state conditions and a RANS model is used to describe turbulent fluid flow. Next, detailed calculations are performed to quantify aerodynamic forces and the pitching moment. The results obtained from the CFD simulations strongly support the results yielded by the VLM calculations. Moreover, it is found that the aircraft is statically stable at the most critical velocities during stall and cruise flight conditions.
  • Trajectory optimization for accompanying satellite obstacle avoidance
    • Abstract: Publication date: November 2018Source: Aerospace Science and Technology, Volumes 82–83Author(s): Qinglei Hu, Jingjie Xie, Xinfu Liu This paper aims at the trajectory optimization problem of an accompanying satellite in the space station under multi-obstacles by model predictive control (MPC) with successive linearization. This optimization problem is reformulated as a mixed integer second-order cone programming (MISOCP) problem by considering the obstacles avoidance, and various physical constraints. More specifically, a novel variation weight cost function is established with the distance information of the accompanying satellite and obstacles, such that a multi-objective optimization performance is achieved by incorporating fuel consumption and time expenditure further. Through the successive linearization of the MPC scheme, the satisfaction of the multiple constraints is established. These results lead to a feasible solution with harsh constraints as well as the fast convergence to the optimal solution. The obstacles avoidance constraints are first implemented through the appropriate selection of initial values, and then solved by successive approximation with the MPC framework for the convergence of solution. Numerical simulation has been conducted to demonstrate the effectiveness and applicability of the proposed method.
  • Characteristics of the combustion chamber of a boron-based solid
           propellant ducted rocket with a chin-type inlet
    • Abstract: Publication date: November 2018Source: Aerospace Science and Technology, Volumes 82–83Author(s): Binbin Chen, Zhixun Xia, Liya Huang, Likun Ma The scope of this study is to improve combustion performance of a boron-based solid propellant ducted rocket (SPDR). A numerical approach for the internal reaction flow in SPDR was built, and an improved ignition and combustion model of boron particles was used. Many integrated physical processes of boron ignition and combustion, such as the balance of (BO)n on particle surface at ignition stage, the evaporation and boiling processes of boron at combustion stage, were considered. A new configuration of SPDR with swirling flow was proposed. Moreover, numerical and experimental investigations were conducted, and the effects of equivalence ratio and swirling flow on combustion performance were analysed. Validation of the developed numerical approach showed good agreement between the approach's results and available experimental data in open literature and also those in this study. Experimental results indicated that combustion efficiencies increase from 88% to 95% with swirling flow.
  • Optimization strategy for a single-stage axisymmetric hub endwall in axial
           compressor by a modified transonic area rule
    • Abstract: Publication date: November 2018Source: Aerospace Science and Technology, Volumes 82–83Author(s): Zhiping Li, Yafei Zhang, Tianyu Pan, Hanan Lu, Miao Wu, Jian Zhang The secondary loss is the primary factor limiting the performance of highly loaded compressors. As inspired by the transonic area rule used in optimization of airplane fuselage, considering the similarities of the blockage effect induced by wing to fuselage and the blockage induced by blade to flow channel, the idea of using the transonic area rule method in compressor hub profile modification has been proposed and discussed. Some related analyses are investigated due to the failure of a direct application of the transonic area rule, which includes flow field analyses, the study of related parameters and a sensitivity evaluation of eleven control parameters on the adiabatic efficiency of the compressor. Then, two parameters (rotor maximum concave displacement ratio ΔZ‾R and magnification ratio of rotor hub leading edge l¯1R) which have great influence on the compressor efficiency are chosen to modify the transonic area rule and to establish a new optimization guideline in the optimization of compressor hub profile. After all, the developed optimization method is applied to the first stage of a four-stage embedded compressor with an achievement of 0.97% peak efficiency rise without any penalty of total pressure ratio. Based on the numerical results, the main reasons for the peak efficiency rise are also presented and discussed.
  • Numerical study of pore-scale flow and noise of an open cell metal foam
    • Abstract: Publication date: November 2018Source: Aerospace Science and Technology, Volumes 82–83Author(s): Chen Xu, Yijun Mao, Zhiwei Hu This paper studies numerically the three-dimensional pore-scale flow inside a single cell structure of an open cell metal foam and its aeroacoustic features. Since the Reynolds number based on the pore diameter is very low, the Navier–Stokes equations are solved directly to simulate the unsteady pore-scale flow. The permeability and pressure drop obtained from numerical simulations are compared with existing reference results. Numerical results reveal that the flow drag of the pore-scale structure is dominated by the pressure drag which is mainly caused by the flow separation, while the friction drag is much smaller than the pressure drag despite a very high surface area–volume ratio of the metal foam. The unsteady flow separation contributes primarily to the pressure drag and causes the self-noise of the metal foam, therefore suppressing the unsteady flow separation, e.g., by optimizing the cell structure of the metal foam, would reduce the drag and aerodynamic noise. The aeroacoustic features, such as noise sources, spectra and the directivity pattern, are investigated, and the results reveal a high correlation between the noise generation and the flow separation. The direction of the maximum sound pressure for the studied cell is parallel to the flow, which is different to flow separation from a cylinder where the direction of maximum radiation is perpendicular to the flow.
  • Aircraft icing safety analysis method in presence of fuzzy inputs and
           fuzzy state
    • Abstract: Publication date: November 2018Source: Aerospace Science and Technology, Volumes 82–83Author(s): Jiaqi Wang, Zhenzhou Lu, Yan Shi For lack of safety measure under the widely existing fuzzy inputs and fuzzy state in the aircraft icing process, a safety analysis model is established to quantify the safety degree of aircraft icing under the fuzzy inputs and fuzzy state. Three-fold contribution is included in the established model. Firstly, by analyzing the recognition capability and properties, the failure credibility model possessing wide recognition capability and self-duality property is selected to measure the safety degree under the fuzzy inputs and binary state. Secondly, by a strictly mathematical derivation, an easily extended definition of the failure probability under random inputs and fuzzy state is proved, on which the failure credibility model under the fuzzy inputs and fuzzy state is established finally. After a numerical example is used to illustrate the feasibility of the established failure credibility model under the fuzzy inputs and fuzzy state in view of different perspectives, a real application of the established model is completed for the safety analysis of an aircraft icing problem.
  • Investigation on self-pressurization and ignition performance of nitrous
           oxide fuel blend ethylene thruster
    • Abstract: Publication date: November 2018Source: Aerospace Science and Technology, Volumes 82–83Author(s): Xuesen Yang, Xin Hong, Wei Dong In this paper, a novel method is developed to analyze the thermal parameters of Nitrous Oxide Fuel Blend Ethylene and establish the saturated vapor pressure relationship with temperature from −80 to 30 °C based on Peng–Robinson equation of state, vapor/liquid phase equilibrium relation and Helmholtz equation. The experiments were conducted to validate the reliability of thermodynamic model. The self-pressurization flow model and sectionalized–centralized parameter gasification model of pipeline are established and validated. A chemical reaction mechanism with 129-species 900-reaction of Nitrous Oxide Fuel Blend Ethylene is established and the flame kernel parameters and laminar flame speed are obtained by steady-state, quasi-one-dimensional reacting flows simulations. Laminar flame speed of nitrous oxide fuel blend ethylene was measured and compared with calculated flame characteristics.
  • Neural network based online predictive guidance for high lifting vehicles
    • Abstract: Publication date: November 2018Source: Aerospace Science and Technology, Volumes 82–83Author(s): Zhenhua Li, Xiangdong Sun, Chen Hu, Gang Liu, Bing He In this paper, a data-driven online entry guidance framework is proposed. Based on the proposed framework, a novel neural network based online predictive guidance algorithm for high lifting vehicles is developed, which combines the benefits of the existing predictive guidance and the neural network predictor. By introducing the neural network predictor, the proposed algorithm can effectively overcome the long-standing contradiction between guidance accuracy and real-time guidance of existing numerical predictive guidance methods. Take the augmented predictor–corrector guidance algorithm as guidance pattern, a large number of sample trajectory data can be generated by performing full envelop trajectory simulations with different perturbation terms. Based on the sample data, the mapping relationship between the real-time flight states of high lifting vehicles and guidance commands is approximated by multi-layer feedforward neural network. By substituting the off-line trained neural network predictor for the trajectory integrations of each guidance cycle in the augmented algorithm, the proposed algorithm can successfully realize the online precision guidance for high lifting vehicles. The simulation results for nominal and dispersed cases show that the proposed algorithm has better performance on real-time capability and robustness than the existing numerical predictive guidance methods, and it is suitable for engineering practice.
  • A hybrid control scheme for attitude and vibration suppression of a
           flexible spacecraft using energy-based actuators switching mechanism
    • Abstract: Publication date: November 2018Source: Aerospace Science and Technology, Volumes 82–83Author(s): Milad Azimi, Ghasem Sharifi A novel energy-based switching logic scenario to design a hybrid thruster/reaction wheel (RW) system is investigated for active vibration suppression of a flexible spacecraft embedded with collocated and Non-collocated configuration of Piezoelectric patches. The system model is obtained using Lagrangian formulation and the finite element method. The control system includes the attitude and vibration controller, designed by Extended Lyapunov Design (ELD)/Strain Rate Feedback (SRF) control technique to take advantage of the globally stabilized feedback control strategy. An attractive feature of the proposed dual-stage system is the switching time, which is model-based and depends on the rigid-flexible body dynamics including PZT actions. Based on this approach, the Multi-objective Genetic Algorithm (MGA) determines the switching point concerning fuel consumption, settling time and vibration energy. The obtained results using a comparative study show the capabilities of the combination of the RWs and thrusters for cost-effective, high precise attitude control and residual vibration suppression of flexible spacecraft in future missions.
  • Equivalent and simplification of nickel-based single crystal plates with
           film cooling holes
    • Abstract: Publication date: November 2018Source: Aerospace Science and Technology, Volumes 82–83Author(s): Zhixun Wen, Yamin Zhang, Zhenwei Li, Zhufeng Yue The mechanical properties of orthotropic material thin-walled plate with close-packed film cooling holes were studied based on the equivalent solid material concept. The equivalent principals of plane stress conditions, plane strain conditions, generalized plane strain conditions and general stress conditions were considered. A simplification method for square and triangular penetration patterns was presented. Extensive numerical simulation results covering different ligament efficiencies, penetration patterns and stress conditions were provided for the directionally solidified superalloy and nickel-based single crystal superalloy to verify the feasibility of equivalent principals and simplification method. Three crystal orientations [001], [011] and [111] of nickel-based single crystal superalloy were analyzed. The stress concentration factors were obtained for the mechanical behavior analysis of cooled blade. The values of equivalent error are all less than 10% when the ligament efficiency is larger than 0.4. The tensile deformation, Mises equivalent stress and stress distribution under the same stress level show the crystal orientation correlation. The tensile deformation of three crystal orientations is: [001]> [011]> [111]. The maximum Mises equivalent stress of [001] orientation and [011] orientation around the film cooling hole are basically the same, and they are all less than [111] orientation. The maximum and minimum values of stress concentration factors are 3.49 and 1.82 respectively.
  • Cooperative aerial lift and manipulation (CALM)
    • Abstract: Publication date: November 2018Source: Aerospace Science and Technology, Volumes 82–83Author(s): Hossein Rastgoftar, Ella M. Atkins This paper proposes a novel paradigm for aerial payload transport and object manipulation by an unmanned aerial vehicle (UAV) team. This new paradigm, called cooperative payload lift and manipulation (CALM), applies the continuum deformation agent coordination approach to transport and manipulate objects autonomously with collision avoidance guarantees. CALM treats UAVs as moving supports during transport and as stationary supports during object manipulation. Constraints are formulated to assure sufficient thrust forces are available to maintain stability and follow prescribed motion and force/torque profiles. CALM uses tensegrity muscles to carry a suspended payload or a manipulation object rather than cables. A tensegrity structure is lightweight and can carry both the tension and compression forces required during cooperative manipulation. During payload transport, UAVs are categorized as leaders and followers. Leaders define continuum deformation shape and motion profile while followers coordinate through local communication. Each UAV applies input–output (IO) feedback linearization control to track the trajectory defined by continuum deformation. For object manipulation, the paper proposes a new hybrid force controller to stabilize quadcopters when smooth or sudden (impulsive) forces and moments are exerted on the system.
  • An analytical study of sound transmission through stiffened double
           laminated composite sandwich plates
    • Abstract: Publication date: November 2018Source: Aerospace Science and Technology, Volumes 82–83Author(s): Tao Fu, Zhaobo Chen, Hongying Yu, Zhonglong Wang, Xiaoxiang Liu The main objective of this research work is focused on sound transmission loss analysis of stiffened double laminated composite sandwich plate structures subjected to plane sound wave excitation, wherein the laminated composite plates are composed of perfectly bonded functionally graded carbon nanotubes (CNTs) reinforced composite layers, and in each layer, the carbon nanotubes is uniform or functionally graded along with the thickness direction of structures, and three types of the CNTs distributions are studied. The extended rule of mixture is employed to determine the properties of the composite material. The compatibility of displacements on the interface between the plate and the stiffeners is employed to derive the governing equation of each stiffener. Then fluid–structure coupling is considered by imposing velocity continuity condition at fluid–structure interfaces. By using the space harmonic approach and virtual work principle, the sound transmission loss is described analytically. Since no existing results of sound insulation can be found for such composite material plate structure, comparison studies can only be made with the isotropic and laminated case. Good agreement is found from these comparison studies. Based on the developed theoretical mode, the influences of the volume fractions of CNTs, distribution type of CNTs, structural damping, lamination angle and the number of layers on sound transmission loss are subsequently presented.
  • Fixed-time extended state observer based non-singular fast terminal
           sliding mode control for a VTVL reusable launch vehicle
    • Abstract: Publication date: November 2018Source: Aerospace Science and Technology, Volumes 82–83Author(s): Liang Zhang, Changzhu Wei, Rong Wu, Naigang Cui This paper is devoted to developing an extended state observer based non-singular fast terminal sliding mode control with fixed-time convergence for a vertical take-off and vertical landing (VTVL) reusable launch vehicle. The six-degree-of-freedom dynamic model of the VTVL is developed, and then the error tracking state equation is established as well. A novel fixed-time extended state observer is presented to estimate the error state and the total disturbances in the presence of nonlinear, couplings, uncertain parameters and external disturbances. Based on the estimation of the error state, a novel non-singular fast terminal sliding mode surface is designed, and the corresponding fixed-time controller is also designed via the estimation of the total disturbances and the proposed sliding mode surface. The stability analysis for the fixed-time extended state observer and the proposed controller are provided. Numerical simulation results are carried out to illustrate the effectiveness of the proposed control scheme.
  • Microstructural characterization and mechanical performance of
           Al–Cu–Li alloy electron beam welded joint
    • Abstract: Publication date: November 2018Source: Aerospace Science and Technology, Volumes 82–83Author(s): Li Zhao, Shaogang Wang, Yang Jin, Yuan Chen Al–Cu–Li alloy with the thickness of 4 mm is welded by electron beam welding (EBW). Microstructure and mechanical properties of welded joint are systematically investigated. The formation mechanism of weld porosity is fully discussed. Orthogonal experiment results show that welding parameters have great effect on the generation of weld gas pore, and welding speed is the main factor affecting the porosity, followed by electron beam scanning mode, electron beam current is the minimal one. Microstructure analysis demonstrates that weldment is mainly equiaxed grains, and some dendrites exist too. Mechanical properties of welded joints indicate that, under the following welding parameters, electron beam current 13 mA, welding speed 600 mm/min, circular electron beam scanning, a welded joint with good mechanical performance can be obtained. Tensile strength of welded joint is 368.4 MPa, which is about 68% of that of the base metal (BM). SEM analysis shows that there are many fine dimples distributed on the fracture surface of welded joint, and it obviously presents the characteristic of ductile fracture.
  • Damage mechanisms of 3-D rectangular braided composite under multiple
           impact compressions
    • Abstract: Publication date: November 2018Source: Aerospace Science and Technology, Volumes 82–83Author(s): Xingzhong Gao, Baozhong Sun, Bohong Gu This paper reports the damage mechanisms of 3-D carbon fiber/epoxy braided composite under multiple impact compressions along out-plane direction. The multiple compression tests were conducted on a split Hopkinson pressure bar (SHPB) apparatus. The compressive deformations and damages were photographed with high speed camera and compared with those from finite element analyses (FEA). We found that the initial compressive damages are fiber/resin interface damage and resin fragmentation. Then the braided preform was in a severe shear damage which accompanied with further damages of interface and resin under the followed impact compressions. The energy absorptions by the reinforcement and epoxy resin at the multiple impacts were decomposed. The braided composite has the highest energy absorption capability at the first impact. The yarn orientation in braided preform leads to non-uniform stress and strain distribution. This non-uniformity easily induced the local damage and furthermore the catastrophic failure under the multiple compressions.
  • Impact of solar wind fluctuations on Electric Sail mission design
    • Abstract: Publication date: November 2018Source: Aerospace Science and Technology, Volumes 82–83Author(s): Lorenzo Niccolai, Alessandro Anderlini, Giovanni Mengali, Alessandro A. Quarta The Electric Solar Wind Sail (E-sail) is a propellantless propulsion system that generates thrust by exploiting the interaction between a grid of tethers, kept at a high electric potential, and the charged particles of the solar wind. Such an advanced propulsion system allows innovative and exotic mission scenarios to be envisaged, including non-Keplerian orbits, artificial Lagrange point maintenance, and heliostationary condition attainment. In the preliminary mission analysis of an E-sail-based spacecraft, the local physical properties of the solar wind are usually specified and kept constant, while the E-sail propulsive acceleration is assumed to vary with the heliocentric distance, the sail attitude, and the grid electric voltage. However, the solar wind physical properties are known to be characterized by a marked variability, which implies a non-negligible uncertainty as to whether or not the solutions obtained with a deterministic approach are representative of the actual E-sail trajectory. The aim of this paper is to propose an effective method to evaluate the impact of solar wind variability on the E-Sail trajectory design, by considering the solar wind dynamic pressure as a random variable with a gamma distribution. In particular, the effects of plasma property fluctuations on E-sail trajectory are calculated with an uncertainty quantification procedure based on the generalized polynomial chaos method. The paper also proposes a possible control strategy that uses suitable adjustments of grid electric voltage. Numerical simulations demonstrate the importance of such a control system for missions that require a precise modulation of the propulsive acceleration magnitude.
  • Semi-analytical prediction of macroscopic characteristics of open-end
           pressure-swirl injector
    • Abstract: Publication date: November 2018Source: Aerospace Science and Technology, Volumes 82–83Author(s): A. Kebriaee, Gh. Olyaei After proposing a semi-analytical solution for swirl laminar flow, macroscopic characteristics of open-end pressure-swirl injector including discharge coefficient and spray cone angle are calculated. In the presence of air core of the axial region inside the injector, the laminar rotational flow equations are simplified, and with the assumption of the quasi-developed axial flow along the nozzle, the equations are iteratively solved employing separation of variables method. The accuracy of the proposed semi-analytical solution is compared by some numerical and experimental results on an open-end injector. The validity of quasi-developed flow defined in the present work is confirmed based on the results of numerical simulations in different axial cross-sections. Moreover, findings demonstrate that the spray cone angle is predicted with an accuracy of about 3.7% for different operating conditions of experimental tests. The calculation of pressure distribution along the liquid film illustrates that viscous effect is negligible in pressure drop in the injector and the discharge coefficient is dominantly dependent on the flow inlet condition in the nozzle. Calculation of discharge coefficient presented in this paper shows an acceptable agreement with observations for different tests. Deviation of the theoretical discharge coefficient is less than 4.37% for various case studies with empirical results.
  • Postbuckling analyses and derivations of Knockdown factors for hybrid-grid
           stiffened cylinders
    • Abstract: Publication date: November 2018Source: Aerospace Science and Technology, Volumes 82–83Author(s): Chang-Hoon Sim, Jae-Sang Park, Han-Il Kim, Ye-Lin Lee, Keejoo Lee In this work, postbuckling behaviors of grid-stiffened cylinders under compressive loads are examined in an attempt to establish an analytical method to derive the shell Knockdown factor for space launch vehicle structures. Two grid systems using stiffeners – traditional orthogrid and hybrid-grid systems – are considered for the stiffened cylinders. The hybrid-grid system consists of major and minor stiffeners, which have two different cross-sectional sizes. Additionally, the baseline and minimum weight models are considered for each grid-stiffened cylinder model. The single perturbation load approach is used to represent the geometrical imperfection of cylinders. A commercial finite element analysis code, ABAQUS, is used for the postbuckling analyses. The present numerical simulations investigate the global and local instabilities for both stiffened cylinders using orthogrid and hybrid-grid systems. The global buckling load for the hybrid-grid stiffened cylinder is higher than that for the traditional orthogrid stiffened cylinder for both the baseline and minimum weight models. However, the postbuckling behaviors for the hybrid-grid stiffened cylinders are more complex, as compared to those for the orthogrid stiffened cylinders. Additionally, the shell Knockdown factors are derived using obtained numerical analysis results for the grid-stiffened cylinders. Since the shell Knockdown factor of the hybrid-grid stiffened cylinder is higher than that of the traditional orthogrid stiffened cylinders for both the baseline and minimum weight models, the hybrid-grid stiffened cylinder is more efficient in terms of the buckling design when compared to a traditional orthogrid stiffened cylinder. Furthermore, the derived Knockdown factors in the present work are higher than the values by NASA's buckling design criteria.
  • Experimental study on the effect of equivalence ratio and injector
           position on flow structure and flame development in the scramjet combustor
    • Abstract: Publication date: November 2018Source: Aerospace Science and Technology, Volumes 82–83Author(s): Ye Tian, Xuejun Zeng, Shunhua Yang, Fuyu Zhong, Jialing Le In order to understand the combustion characteristic clearly in the scramjet combustor, the effect of equivalence ratio and injector position on flow structure and flame development in a hydrogen fueled scramjet combustor was investigated experimentally in the present paper, various measurements included schlieren, shadow, differential interferometry, flame emission and OH*-PLIF were made during the experiments in an attempt to better understand the combustion flow field. The results were obtained under the inflow condition of Ma2.0, total temperature and total pressure were 950 K and 0.82 MPa, respectively. The combustion induced backpressure had not spread into the isolator when the equivalence ratio was 0.1, the flow structure was stable and the flame was located in the cavity shear layer in a line shape. But the backpressure of the cases when the equivalence ratio was 0.3 had spread into the isolator, the flow structure was unstable and the flame existed both in the cavity and in the core flow in a shredded paper shape. The hydrogen injected from the upstream injector burnt more intensively than that injected from the downstream injector under the same equivalence ratio condition. The above mentioned non-intrusive measuring methods had their own limitations, but the synchronous measurement method could well show a more comprehensive coupling information of the flow structure and combustion characteristics.
  • Assessment of transition regimes in a dual-bell nozzle and possibility of
           active fluidic control
    • Abstract: Publication date: November 2018Source: Aerospace Science and Technology, Volumes 82–83Author(s): Vladeta Zmijanovic, Luc Leger, Mohamed Sellam, Amer Chpoun Dual-bell axisymmetric propulsive nozzle, as the most prominent altitude compensating nozzle concept has been investigated for transition modes and effects. Experimental and numerical investigations show that dual-bell nozzle can be very effective for desired large envelope launcher stage trajectories. Transition regimes are studied in the high altitude simulation wind-tunnel and supported by the numerical simulations. Analysis of the employed diagnostics shows an existing particular hysteresis between the transitioning modes and pinpoints to possibilities to control the early transition. Further numerical investigation on active flow control indicates the promising potentials of the proposed fluidic injection system.
    • Abstract: Publication date: Available online 25 October 2018Source: Aerospace Science and TechnologyAuthor(s): E.A. Salgansky, N.A. Lutsenko, V.A. Levin, L.S. Yanovskiy A novel mathematical model and a numerical method for studying the gasification of solid fuel in a combined charge of a low-temperature gas generator for high-speed flying vehicle with a sequential arrangement of a propellant and a fuel for generation of hydrocarbon gases are proposed. This scheme assumes the organization of cooling of the ramjet engine by means of a convective flow of gasification products of evaporable solid fuel. The calculations of the operating regimes of the gas generator with the characteristics of solid fuel as in polymethylmethacrylate are carried out. The operating time of ramjet engine of high-speed flying vehicle is estimated. It is shown that the operating time of the ramjet engine with a low-temperature gas generator increases with a decrease in the temperature of the gaseous combustion products of the propellant, the coefficient of interphase heat transfer, the fuel permeability coefficient and the inlet pressure in the gas generator.
  • Least squares support vector machine for class imbalance learning and
           their applications to fault detection of aircraft engine
    • Abstract: Publication date: Available online 24 October 2018Source: Aerospace Science and TechnologyAuthor(s): Peng-Peng Xi, Yong-Ping Zhao, Pei-Xiao Wang, Zhi-Qiang Li, Ying-Ting Pan, Fang-Quan Song Imbalanced problems often occur when the size of majority class is bigger than that of the minority one. The Least squares support vector machine (LSSVM) is an effective method for solving classification problem on balanced datasets. However, LSSVM has bad performance on minority class facing with class imbalance learning for the classification boundary skewing toward the majority class. In order to overcome the drawback, LSSVM for class imbalance learning (LSSVM-CIL) is proposed. LSSVM-CIL utilizes two different regularization parameters C+ and C− that evaluate different misclassification costs. Furthermore, a method of combining reduced technique and recursive strategy is proposed to reduce the size of support vectors and retain representative samples. In addition, decomposition of the matrices via Cholesky factorization is employed as a solution to enhance the computational stability. Furthermore, the effectiveness of the two algorithms presented in this paper is confirmed with experimental results on various real-world imbalanced datasets. Fault detection of aircraft engine can be regarded as a CIL problem and has the demand for the real time. Finally, experiments on aircraft engine indicate that the two algorithms can be selected as candidate techniques for fault detection of aircraft engine.
  • Integrated strapdown missile guidance and control based on neural network
           disturbance observer
    • Abstract: Publication date: Available online 24 October 2018Source: Aerospace Science and TechnologyAuthor(s): Bin Zhao, Siyong Xu, Jianguo Guo, Ruimin Jiang, Jun Zhou This paper investigates one integrated guidance and control (IGC) method for missiles with strapdown seeker. The IGC model considering the field-of-view (FOV) constraint is built by employing the strapdown decoupling method, based on which the strict feedback state equation with unmatched uncertainties is derived. The system uncertainties are tackled by neural network (NN) disturbance observer. To handle state constrain issue, the integral Barrier Lyapunov function (iBLF) is employed with the dynamic surface control (DSC) method to deal with the unmatched uncertainties. Then, the uniform ultimately boundedness of the system is proved and the FOV constraint is also guaranteed. Numerical simulation results demonstrate the effectiveness of the proposed control scheme.
  • Application of endwall contouring in a high-subsonic tandem cascade with
           endwall boundary layer suction
    • Abstract: Publication date: Available online 24 October 2018Source: Aerospace Science and TechnologyAuthor(s): Longxin Zhang, Songtao Wang, Wei Zhu A proper combination of active and passive flow control methods would be a promising way to further enhance the compressor performance. This numerical investigation presents a new attempt of application of endwall contouring in a high subsonic tandem cascade with the endwall boundary layer suction implemented in the forward blade. The study aims to further improve the corner flow in the rear blade at design and lower incidences. The planar endwall is redesigned using the optimization method. Nonuniform rational B-spline surface is employed to parameterize the endwall surface. A multi-points optimization strategy is selected to minimize the aerodynamic loss generated in the cascade. In the optimization, the suction strategy remains unchanged. To clarify the impacts of endwall contouring on the cascade performance, flow details in both mainflow passage and suction flow path at design and off-design incidences are analyzed.As a result, the total loss decreases by 8.4% at the design incidence via the endwall contouring. Furthermore, a more prominent loss reduction can be achieved at lower incidences. However, the control effects of endwall contouring is weakened towards higher positive incidences. Worse still, even a deterioration in the cascade performance can be detected at I = 5° due to the presence of a small-scale corner stall in the forward blade. The results indicate that, as the gap flow is not strong enough to counteract the endwall secondary flow, the endwall contouring could be employed to further enhance the flow control ability of the previous proposed compound flow control method, while its negative impact on the cascade performance at higher positive incidences still remains to be addressed.
  • Modeling for solar array drive assembly system and compensating for the
           rotating speed fluctuation
    • Abstract: Publication date: Available online 24 October 2018Source: Aerospace Science and TechnologyAuthor(s): Yuteng Cao, Dengqing Cao, Jin Wei, Wenhu Huang A dynamic model of the solar array drive assembly (SADA) system consisting of a stepper motor and two flexible solar arrays is investigated. The fluctuation compensation of the rotating speed and vibration suppression is studied by integrating the sliding mode control (SMC) method and input shaping (IS) technique. The dynamic equations of the system are derived by the Hamiltonian Principle. The linearized form of the nonlinear dynamic equations with boundaries conditions is adopted to obtain the natural frequencies and global modes of the solar arrays. Based on the electromechanical dynamics model of the stepper motor, a cooperative compensation scheme is designed to achieve the stability of solar arrays and the suppression of system vibration. Numerical results show that the driving speed is significantly influenced by the harmonic torque and the structural vibration of payload. The SMC method compensates for the rotating speed fluctuation much better than the pure feed-forward operation used in the traditional stepper motor. The system with SMC method and IS technique performs much better than the case without vibration suppression.
  • Trajectory optimization for a TBCC-powered supersonic vehicle with
           transition thrust pinch
    • Abstract: Publication date: Available online 24 October 2018Source: Aerospace Science and TechnologyAuthor(s): Jialin Zheng, Juntao Chang, Shengbo Yang, Xinyue Hao, Daren Yu Transition thrust pinch is a critical issue of Turbine-Based-Combined Cycle engines when vehicles operate at trajectories with constant dynamic pressures. The insufficiency of the net thrust might cause that the vehicle fails to accelerate over mode transition from a turbine engine to a scramjet engine and then lead to mission abortion. Existed solutions to this problem mainly focus on increasing thrust of propulsion systems by using auxiliary power units when transition thrust pinch occurs. Without bothering to develop new propulsion systems, this paper turns to trajectory optimization to change the thrust and drag status of the vehicle to gain an additional net thrust. Additionally, the gravity-assist strategy is also used to make up for the thrust pinch in optimized trajectories. The transition thrust pinch issue is abstracted into an optimal control problem with the maximum terminal speed as the cost function, which is then solved via the Gauss pseudospectral method. Firstly, the effectiveness of this strategy is demonstrated by several cases with transition thrust pinch issues. Then, the upper-limit of this method is analyzed. Finally, this study indicates that the limited capacity can be broaden by loosening the constraint on the minimum dynamic pressure.
  • Cooperative load transportation using multiple UAVs
    • Abstract: Publication date: Available online 24 October 2018Source: Aerospace Science and TechnologyAuthor(s): Behzad Shirani, Majdeddin Najafi, Iman Izadi The aim of this paper is cooperative task assignment to multiple unmanned aerial vehicles (UAV) for load transportation. The main goal is to transport a slung load safely with minimal swing. To this end, for each UAV, which is regarded as an agent, a distributed controller is proposed. The proposed controller guarantees a fixed formation, which in turn achieves the main objective. A model of the system is obtained using the Udwadia–Kalaba method for an arbitrary number of UAVs and one slung load with ropes. This method leads to a novel multi-agent system model with interactions between neighbor and non-neighbor agents. The control law is then proposed based on sub-optimal LQR-PID for the extended system. Simulation results are presented to verify the ability of the proposed method to keep the formation of the agents, and to guide the load in the desired direction.
  • An aerothermodynamic design optimization framework for hypersonic vehicles
    • Abstract: Publication date: Available online 24 October 2018Source: Aerospace Science and TechnologyAuthor(s): Simone Di Giorgio, Domenico Quagliarella, Giuseppe Pezzella, Sergio Pirozzoli In the aviation field great interest is growing in passengers transportation at hypersonic speed. This requires, however, careful study of the enabling technologies necessary for the optimal design of hypersonic vehicles. In this framework, the present work reports on a highly integrated design environment that has been developed in order to provide an optimization loop for vehicle aerothermodynamic design. It includes modules for geometrical parametrization, automated data transfer between tools, automated execution of computational analysis codes, and design optimization methods. This optimization environment is exploited for the aerodynamic design of an unmanned hypersonic cruiser flying at M∞=8 and 30 km altitude. The original contribution of this work is mainly found in the capability of the developed optimization environment of working simultaneously on shape and topology of the aircraft. The results reported and discussed highlight interesting design capabilities, and promise extension to more challenging and realistic integrated aerothermodynamic design problems.
  • Nonlinear filtering in unknown measurement noise and target tracking
           system by variational Bayesian inference
    • Abstract: Publication date: Available online 24 October 2018Source: Aerospace Science and TechnologyAuthor(s): Xingkai Yu, Jianxun Li, Jian Xu This paper considers a class of nonlinear filtering algorithms based on variational Bayesian (VB) theory to settle the unknown measurement noise problem in target tracking system. When the unknown measurement noise is conditionally independent of states, based on the variational idea, estimate of probability density function of state is converted into approximation two probability density functions for both unknown noise and nonlinear states. Then, an iterative algorithm is established to jointly estimate the state and the unknown measurement noise using variational Bayesian inference. Thus, the unknown measurement noise could be estimated as hidden state. The convergence result of the proposed nonlinear probability density function approximation algorithm is also given. The simulation results of typical examples show that the proposed VB based methods have superior performance to these classic algorithms in target tracking problems.
  • Nonlinear Supersonic Flutter for the Viscoelastic Orthotropic Cylindrical
           Shells in Supersonic Flow
    • Abstract: Publication date: Available online 23 October 2018Source: Aerospace Science and TechnologyAuthor(s): B.A. Khudayarov, F.J. Turaev On the example of an orthotropic shell, the problems of the dynamics of thin-walled structures under aerodynamic loading are studied, taking into account the viscoelastic properties of material and geometric nonlinearity. The aerodynamic pressure is determined using the AA. Ilyushin's piston theory. Equations of motion relative to displacements are described by a system of integro-differential equations in partial derivatives. Using the Bubnov–Galerkin method, based on the polynomial approximation of deflections, the problem is reduced to a system of ordinary integro-differential equations, where time is an independent variable. Solutions of integro-differential equations are determined by a numerical method based on the elimination of the singularity in the relaxation kernel of the integral operator. Computational algorithms and applied programs have been developed to solve the problems on the nonlinear flutter for viscoelastic elements of an aircraft. The critical flutter speed for the viscoelastic orthotropic cylindrical shells is determined. It is established that an account of viscoelastic properties of shell material leads to a decrease in the critical flutter.
  • Flexible all-plastic aircraft models built by additive manufacturing for
           transonic wind tunnel tests
    • Abstract: Publication date: Available online 23 October 2018Source: Aerospace Science and TechnologyAuthor(s): Weijun Zhu, Xiaoyu Zhang, Dichen Li Wind tunnel testing is considered as a reliable tool, especially for the high-order non-linear aerodynamic problems of large aircraft with high-aspect-ratio wings at transonic speeds. Thanks to its capacity to manufacture complex structures quickly, the introduction of the additive manufacturing (AM) technique into the design and fabrication of testing models can improve the testing performance significantly. However, these AM-built models so far are limited to low-speed testing due to the low strength and modulus of non-metal materials, epoxy resins mostly, used in popular AM processes for aircraft models. The easy-deformation properties are usually considered as the major weakness and many methods are adopted to strengthen the plastic models for high speed tests. Taking advantage of the properties, however, this paper proposes a plastic flexible testing model with a specific pre-deformation that can be deformed into the desired state during wind tunnel tests. To obtain the pre-deformation quantitatively, an optimization formulation was developed based on the coupling of computational fluid dynamics (CFD) and computational structural dynamics (CSD). As a case study, testing models with the DLR (German Aerospace Center) F4 configuration were designed and fabricated by stereolithography (SL), a popular AM process. After the strength calibration, the plastic models were tested in a transonic wind tunnel. All the models performed normally in the harsh condition when the Mach number reached 0.85, and the resulting lift coefficients (CL) obtained by the plastic models showed good consistence with their metallic counterparts. This indicates that the plastic models of large aircraft made by SL could be used in wind tunnel tests at transonic speeds. However, the all plastic models can only be used in a single combination of testing condition. Further studies should be conduct to extend the scope of application of the models. In conclusion, due to AM's capacity to manufacture complex structures with low-modulus materials, flexible models could be designed and built quickly in an economic way. The method could be used in the conceptual design for configuration screening of high-aspect-ratio aircraft, and the paper would provide a new test scheme that is fast and reliable for aircraft design.
  • RANS investigation of the effect of pulsed fuel injection on scramjet
           HyShot II engine
    • Abstract: Publication date: Available online 22 October 2018Source: Aerospace Science and TechnologyAuthor(s): Song Chen, Dan Zhao Effective and efficient fuel–air mixing plays a critical role in the successful operation of scramjet engines. To enhance the fuel–air mixing in supersonic combustion systems with a short flow residence time, the pulsed fuel injection strategy in a realistic scramjet combustor flow condition provided by the HyShot II is numerically studied in this work. For this, 2D and 3D simulations of the hydrogen fueled HyShot II scramjet with pulsed fuel injections are performed. Emphasis is placed on the cold flow field characteristics and fuel–air mixing performance in the combustor. Reynolds-Averaged Navier–Stokes equations are solved with the implementation of the two equation k–ω SST turbulence model via using the ANSYS FLUENT v17.1. The pulsed fuel injection is numerically achieved by implementing a time-dependent total pressure pulse with the shape of a square wave. The total pressure peak is maintained as same as the one that chokes the fuel injector in steady operations. The numerical model is validated first by comparing the results with the experimental data available in the literature. It is then used to study the effect of the pulse injection with different frequencies. It is found that complicated waves structures are formed inside the fuel injector in pulsed fuel injections due to the total pressure pulse. These waves transport outside the fuel injector and lead to the fuel streams with wavy patterns and the unsteady shock structures in the combustion chamber. Fuel penetration depths are not found to be increased for pulsed injections in this study, but much high turbulent kinetic energy (TKE) levels are observed especially inside the fuel injector. With the help of increased TKE, mixing efficiency is found to be improved for all of the pulsed fuel injection by up to 30%. This mixing improvement also strongly depends on the frequency applied.
  • Assessment of S-76 rotor hover performance in ground effect using an
           unstructured mixed mesh method
    • Abstract: Publication date: Available online 22 October 2018Source: Aerospace Science and TechnologyAuthor(s): Je Young Hwang, Oh Joon Kwon In the present study, the aerodynamic performance of an S-76 rotor in hover was numerically investigated by using an unstructured mixed mesh flow solver. The study was made for the rotor for both OGE (out-of-ground-effect) and IGE (in-ground-effect) conditions, and the results are compared against each other. In the present mixed mesh methodology, body-fitted prismatic/tetrahedral mesh was adopted in the near-body flow domain to treat complex geometries easily and to capture the viscous layer on the solid surface more accurately, while in the off-body region away from the blades Cartesian mesh was used. To better resolve the flow characteristics and to prevent excessive numerical dissipation, a high-order accurate weighted essentially non-oscillatory (WENO) scheme was employed in the off-body flow region. An overset mesh topology was adopted to handle blade rotation and to exchange the flow variables between the two different mesh regions. The calculations were made for three different blade configurations, having swept-tapered, rectangular, and swept-tapered-anhedral tip shapes, and the results are compared with experimental rotor performance data in terms of thrust, torque and figure of merit. The predictions were obtained for a collective pitch angle sweep from 5 to 10 degrees at a tip Mach number of 0.60 for both with and without ground effects. The detailed flow characteristics, such as vorticity contours and tip-vortex trajectory, were also investigated.
  • Multiphysics modeling and experimental validation of low temperature
           accumulator for cryogenic space propulsion systems
    • Abstract: Publication date: Available online 17 October 2018Source: Aerospace Science and TechnologyAuthor(s): S. Torras, J. Castro, J. Rigola, S. Morales-Ruiz, J. Riccius, J. Leiner Within the framework of Low Thrust Cryogenic Propulsion (LTCP) systems, a low-temperature accumulator acting as thermal energy storage tank is an interesting option for cyclical processes under intermittent firings avoiding the use of turbopumps in the cryogenic stages. Thus, liquid propellant (oxygen, hydrogen or methane) can be gasified under a fast transient evaporation process cooling the accumulator. On the other hand, the same accumulator can be heated by solar collectors, electrical heaters or by means of evaporated propellants recovering heat losses from fuel cells. To obtain a very high thermal energy storage density, the thermal energy stored in the accumulator is performed using a Phase Change Material (PCM) rounding the different fluid flow tubes which heat or cool the storage tank during periodical cycles. The energy management due to the mismatch between intermittent firings, together with optimum design based on minimum weight with maximum heat transfer capacity has led to developing a numerical simulation model. Thermal and fluid dynamic behavior of multi-physics phenomena in the accumulator is based on coupling the two-phase flow inside tubes working under cryogenic conditions with sensible and latent heat transfer through the tank. The numerical model is divided into: 1) a one-dimensional and transient resolution of the governing equations (conservation of mass, momentum, and energy) for the fluid flow inside ducts; 2) a multi-dimensional and transient resolution of the governing equations in the region occupied by the PCM, incorporating a turbulence model to solve the convection phenomena involved; and 3) a multidimensional and transient treatment of the thermal conduction equation for the solid tubes. The numerical results are validated by means of an experimental cylindrical accumulator test facility, instrumented with 25 thermocouples around the vertical tube which goes through the tank and four multilevel thermocouples columns at different distances radially far from the vertical tube located at the center. The comparative analysis shows a good agreement between both numerical results and experimental data for a wide range of different working conditions showing detailed phenomena analysis, together with the possibilities of this model for design optimization purposes.
  • A novel distributed extended Kalman filter for aircraft engine gas-path
           health estimation with sensor fusion uncertainty
    • Abstract: Publication date: Available online 17 October 2018Source: Aerospace Science and TechnologyAuthor(s): Feng Lu, Tianyangyi Gao, Jinquan Huang, Xiaojie Qiu This paper is concerned with state estimation approach to track aircraft engine gas-path health condition in an advanced distributed architecture. The sensor measurements are divided into several subsets by installation position along gas path, and they are integrated to estimate engine health state changes with sensor fusion uncertainty. The uncertain sensor fusion is characterized by time delay and packet dropout in the fusion behavior of sensor measurements, and the delay steps occur randomly. A novel distributed extended Kalman filter with the data buffer bank (DEKF) is developed, and self-tuning buffer strategy of recursive fusion estimation is combined to the DEKF to form the self-tuning DEKF (SDEKF) algorithm for improving state estimation performance. The lengths of data buffer bank related to the local filters of SDEKF are different, and they are independently adaptive to the information loss level and local estimation accuracy. Local states are calculated using the measurements collected at the latest steps in self-tuning buffer banks, and then sent to master filter to yield global state and covariance by fusion estimation. The contribution of this study is to propose a novel EKF algorithm for state estimation in the distributed framework with sensor fusion uncertainty, and it achieves better trade-off between the estimation accuracy and computational efforts. The systematical comparisons of basic EKF, constant buffer DEKF and SDEKF algorithms are carried out for aircraft engine gas-path health estimation with sensor fusion uncertainty. The simulation results show the superiority of the SDEKF, and it confirms our viewpoints in this paper.
  • Research on control-oriented coupling modeling for air-breathing
           hypersonic propulsion systems
    • Abstract: Publication date: Available online 16 October 2018Source: Aerospace Science and TechnologyAuthor(s): Dong Zhang, Shuo Tang, Lin Cao, Feng Cheng, Fan Deng A control-oriented coupling hypersonic propulsion system model is proposed to enable the rapid development of a propulsion model for air-breathing hypersonic flight vehicles (ABHV) in early stages of the design process and facilitate design control and analysis. An airframe/propulsion coupling hypersonic inlet model was established based on oblique shock wave theory. An isolator model in which the effects of the back pressure of the combustion chamber were adjusted by the static pressure ratio of the isolator was established. A hypersonic combustion model was also established, taking into account the fuel flow, cross-sectional area, wall friction, combustion efficiency, and exothermic reactions based on quasi-1D flow theories. Nozzle/afterbody modeling was established based on identification of the free boundary (i.e., the location of the shear layer) by Newton collision theory, and flow parameters were determined according to the influence coefficient method. The mass flow rates of air in the design state and two typical non-design states were determined geometrically based on the application of oblique shock wave theory. A propulsion coupling model that reflects the coupling of propulsion system and aerodynamics, as well as the physical mechanisms of the propulsion mechanism, was then established based on air flow rates obtained and the momentum theorem. Simulation results of airframe/propulsion integrated module air-breathing hypersonic flight vehicles (ABHVs) by the proposed model were compared to results achieved by numerical 3D Computational Fluid Dynamics (CFD) models. Results indicated that the efficacy and accuracy of the proposed models met the established requirements of control-oriented modeling, thus facilitating dynamic modeling and control in the early stage of the design process.
  • Adaptive control for hypersonic vehicle with input saturation and state
    • Abstract: Publication date: Available online 16 October 2018Source: Aerospace Science and TechnologyAuthor(s): Hai-Yan Qiao, Hao Meng, Meng-Jun Wang, Wei Ke, Jing-Guang Sun The tracing control problem of hypersonic vehicle subject to external disturbances, parametric uncertainties, input saturation and state constraints. Firstly, the longitudinal model of the hypersonic vehicle is converted to the velocity subsystem and altitude subsystem based on the functional decomposition. Secondly, two adaptive anti-saturation controllers are proposed for the velocity subsystem and altitude subsystem with the unknown upper bound of external disturbances. By using the asymmetric barrier Lyapunov function, the two controllers can make flight path angle, angle of attack and pitch angle rate keep within the certain ranges. Meanwhile, the auxiliary system is introduced to deal with the problem of input saturation and a low-pass filter is designed to avoid the “explosion of terms” in traditional backstepping control caused by the complicated differentiations of the virtual control signals. Finally, the effectiveness of the presented control strategy is verified by the Lyapunov stability theory and numerical simulations results.
  • Method and numerical simulation for evaluating the effects of water film
           on the performance of low-speed axial compressor
    • Abstract: Publication date: Available online 15 October 2018Source: Aerospace Science and TechnologyAuthor(s): Lu Yang, Jie Zhou, Shuangming Fan, Qun Zheng, Hai Zhang Numerical simulations for a low-speed axial compressor under water ingestion are performed to evaluate the aerodynamic performance degradation due to the formation of water film. The water film thickness on a blade surface is calculated by a self-compiled program developed by the authors. In addition, the blade surface is divided into several regions, which can be roughened separately, to elucidate the characteristics of the nonuniform water film. The equivalent sand roughness corresponding to the root-mean-square water film thickness are specified for the blade surface to simulate the aerodynamic losses of the blade row caused by water deposition. The results show that the water film thickness is positively correlated with the water content, and negatively correlated with the compressor outlet pressure. The overall compression performance presents a downtrend after water ingestion. When the water content increased from 0.37% to 4.02%, the compression efficiency deteriorated by 1%–3% compared with the dry condition. The distribution of the static pressure coefficient on the blade surface is also changed, wherein the deviation degree at the tip region is greater than that at the hub region. Unfortunately, considering the limitations of the current water film models and computational methods, the water film formed on the tip region cannot be simulated. Therefore, the calculated results near the stall point are different from the experimental results. However, rough surface treatment can still be considered as a feasible method for evaluating the effects of water film on compressor performance.
  • Fuzzy multiobjective cooperative surveillance of multiple UAVs based on
           distributed predictive control for unknown ground moving target in urban
    • Abstract: Publication date: Available online 13 October 2018Source: Aerospace Science and TechnologyAuthor(s): Chaofang Hu, Zelong Zhang, Na Yang, Hyo S. Shin, Antonios Tsourdos In this paper, a fuzzy multiobjective path planning method based on distributed predictive control is proposed to deal with the problem of cooperative searching and tracking of unknown ground moving target by multiple unmanned aerial vehicles (UAVs) in urban environment. Firstly, extended Kalman filter (EKF) is combined with probability estimation to predict the states of the unknown target. Secondly, the line of sight occlusion of buildings, and energy consumptions of UAVs and sensors are considered in path planning. The objective functions are designed as target coverage degree, control input cost of UAV and sensor energy consumption respectively. The cooperative surveillance path planning problem is transformed into multiobjective optimization with different importance levels. Thirdly, distributed predictive control is used to obtain the local optimal path of each UAV. The predictive states of UAVs in finite horizon are exchanged to build the collision avoidance constraint, and the minimum turning radius constraint is also addressed. Then, all the objectives are fuzzified to handle the different importance level requirement. The sensor energy consumption function with switch value is equivalently converted using Sigmoid function and sign function. According to the principle that the objective with higher priority has higher satisfactory degree, preemptive priorities are transformed into the relaxed order of satisfactory degrees. The best path satisfying the requirement of multiobjective optimization and importance levels can be obtained. Finally, the simulation results show the effectiveness of the proposed method by comparing with traditional multiobjective weighted algorithm.
  • Persistent standoff tracking guidance using constrained particle filter
           for multiple UAVs
    • Abstract: Publication date: Available online 12 October 2018Source: Aerospace Science and TechnologyAuthor(s): Hyondong Oh, Seungkeun Kim This paper presents a new standoff tracking framework of a moving ground target using UAVs with limited sensing capabilities and motion constraints. To maintain persistent track of the target even in case of target loss for a certain period, this study predicts the target existence area using the particle filter and produces control commands that ensure that all predicted particles can stay within the field-of-view of the UAV sensor at all times. To improve target position prediction and estimation accuracy, the road information is incorporated into the constrained particle filter where the road boundaries are modelled as inequality constraints. Both Lyapunov vector field guidance and nonlinear model predictive control-based methods are applied, and the characteristics of them are compared using numerical simulations.
  • Two-time-scale control of a multirotor aircraft for suspended load
    • Abstract: Publication date: Available online 11 October 2018Source: Aerospace Science and TechnologyAuthor(s): Emanuele L. de Angelis, Fabrizio Giulietti, Goele Pipeleers This paper presents a trajectory control strategy for a multirotor aircraft carrying a suspended load. The load is modeled as a pendulum connected by a rigid link to the center of gravity of the vehicle. Starting from the dynamic equations describing the motion of the coupled vehicle slung-load systems, a nonlinear controller is proposed that simultaneously performs trajectory tracking and payload swing damping. Controller gains are chosen so that the system exhibits a two-time-scale behavior, with fast dynamics for the pendulum and slow dynamics for the positioning task. Under these conditions, the basic results of singular perturbation theory are evoked for both the proof of stability and the preliminary design of control gains. Results of numerical simulations are provided in order to assess the stability and performance of the considered approach.
  • Analytical entry guidance for coordinated flight with multiple no-fly-zone
    • Abstract: Publication date: Available online 11 October 2018Source: Aerospace Science and TechnologyAuthor(s): Wenbin Yu, Wanchun Chen, Zhiguo Jiang, Wanqing Zhang, Penglei Zhao This paper addresses the problem of coordinating a group of Hypersonic Glide Vehicles (HGVs) for the goal of simultaneous arrival in the presence of multiple No-Fly Zones (NFZs). Firstly, a high-precision analytical solution of flight time is derived from the nonlinear entry dynamics model built over a spherical and rotating Earth. Next, an entry guidance considering multi-NFZs and flight-time constraints is designed based on the new analytical flight-time formula as well as the existing 3-D analytical gliding-trajectory formulae. In the longitudinal part of the guidance, the flight-time and downrange formulae are used jointly to plan the longitudinal reference profile by considering both energy-management and flight-time requirements. In the lateral part, the downrange and crossrange formulae are used to plan the bank-reversal sequence according to the NFZ constraints. Additionally, in order to improve the accuracy of terminal time, speed, and altitude, a multi-objective iterative planning scheme employing onboard trajectory simulation is put forward and enabled at a time between the last two bank reversals to fine-tune the remaining short trajectory. In this scheme, the quasi-Newton method is improved by the use of directional derivatives such that the number of the trajectory simulations required to calculate the Jacobian matrix is reduced from 3 to 2 in each iteration, which greatly reduced the amount of calculation. Finally, a flight-time coordination scheme is developed for multiple HGVs to determine the starting times of entry flight, which can further determine the launch times once the boost guidance is specified. The superior performance of the guidance is demonstrated by Monte-Carlo simulations in stochastic disturbed circumstances.
  • Optimum attitude planning of near-space solar powered airship
    • Abstract: Publication date: Available online 9 October 2018Source: Aerospace Science and TechnologyAuthor(s): Weiyu Zhu, Jun Li, Yuanming Xu The attitude of Near-space airship including yaw, roll and pitch angle is important to the output performance of airship solar array. The yaw angle of airship can be controlled without affecting airship mission execution in the quasi-zero wind layer of near-space. This paper aims to improve solar energy system of near-space airship by optimizing airship yaw angle. Based on the solar radiation model and solar array energy model, a MATLAB program is established to calculate the output power. For model validation, solar radiation and output power are simulated and compared with experimental results. The optimum yaw angle for a whole year is obtained with optimization model based on genetic algorithm. The effect of airship shape parameters including the slenderness ratio and the ratio of forebody length to total length (L1/L) is elaborated. The results show that the effect of yaw angle on output power is greater at higher latitude than that at lower latitude and the solar array output energy can be remarkable increased after adjusting yaw angle of airship according to the optimization result. Although the optimal yaw angle is different with the change of working date and latitude, the optimum values mainly lie in 0° and 180°. Moreover, the optimal yaw angle is barely changed, when the slenderness ratio and L1/L of airship are greater than 0.3 and 0.25, respectively. The result has great valuable engineering reference in attitude planning of near-space airship and other aerospace vehicle for energy improvement.
  • Continuous finite-time extended state observer based fault tolerant
           control for attitude stabilization
    • Abstract: Publication date: Available online 9 October 2018Source: Aerospace Science and TechnologyAuthor(s): Bo Li, Qinglei Hu, Yongsheng Yang This work investigates the challenging problem of fast robust fault tolerant attitude control for spacecraft to handle external disturbances, actuator failures and misalignments. More specially, a novel nonsingular terminal sliding mode based finite-time extended state observer is first designed to estimate and compensate for the lumped system faults or uncertainties. And the proposed extended state observer is analysed and proved to be stable in the sense of fast finite-time uniformly ultimately bounded stability. Then, utilizing the techniques of super-twisting and terminal sliding mode control synthetically, a novel continuous attitude control algorithm is developed. The finite-time stability of the closed-loop attitude control system is proved by using a continuously-differentiable, homogeneous and strict Lyapunov function. And also the proposed control scheme is continuous with the property of chattering restraining. Finally, some numerical simulation results are shown to verify the effectiveness and superior performances of the spacecraft attitude stabilization control system driven by the proposed fast robust fault tolerant attitude control scheme.
  • Bird-striking damage of rotating laminates using SPH-CDM method
    • Abstract: Publication date: Available online 9 October 2018Source: Aerospace Science and TechnologyAuthor(s): Yadong Zhou, Youchao Sun, Wenchao Cai Bird strike represents a major hazard to civil aviation. In this paper, impact damage under high velocity is numerically investigated by means of non-linear explicit finite element analysis. We mainly focus the influence of rotational speeds on damage modes and energy variations of bird impact on a circular laminated plate. The Smoothed Particle Hydrodynamics method and an equation of state were employed for the bird projectile. A Continuum Damage Mechanics approach has been applied to simulate failure initiation and damage evolution in unidirectional composite laminates. Hashin's failure initiation criteria have been employed to be able to distinct lamina failure modes. Two damage regimes are identified with respect to the rotational speeds, i.e. impact-dominated damage and rotation-dominated damage. A threshold rotational speed exists for the rotating thin plate in terms of damage regimes. The results can serve as design guidelines in future full-scale or part-scale study of rotating laminated structures.
  • Non-destructive evaluation of Through-thickness permeability in 3D woven
           fabrics for composite fan blade applications
    • Abstract: Publication date: Available online 4 October 2018Source: Aerospace Science and TechnologyAuthor(s): Ma Ali, R. Umer, Ka Khan, S. Bickerton, W.J. Cantwell In this study, we propose a non-destructive modelling framework, with an ability to obtain computational models for numerical prediction of resin flow through 3D fabrics (commonly used in engine fan blade applications) at multiple fiber volume fractions using a single experiment. The work involves extracting real-time geometrical features of two types of 3D reinforcements during an in-situ compaction experiment using micro CT. The 3D image slices obtained at four different thicknesses were converted to computational models. The fiber tows and inter-tow gaps were modeled as distinct phases. The gap analysis and geometrical measurements revealed significant differences in the preform microstructure investigated at different thicknesses. This was followed by a detailed flow analysis using two different commercial software packages. The exported mesh was analyzed in GeoDict® and Ansys Fluent® for through-thickness permeability computations. The governing fluid dynamics equations were solved to obtain the flow field within the inter-tow gaps for representative volume elements. The predicted through-thickness permeability values were in very good agreement with the experimental data.
  • A Comprehensive Analytical Study on Functionally Graded Carbon
           Nanotube-Reinforced Composite Plates
    • Abstract: Publication date: Available online 4 October 2018Source: Aerospace Science and TechnologyAuthor(s): Behrouz Karami, Davood Shahsavari, Maziar Janghorban This paper presents a model which is effective and simple based upon Second Order Shear Deformation Theory (SSDT) to comprehensive study of Functionally Graded Carbon Nanotube Reinforced Composite (FG-CNTRC) plates including size effects for the first time. Also it is the first time that the size-dependent static, stability and dynamic response of FG-CNTRC plates considering Winkler-Pasternak elastic foundation effects are investigated. It is assumed that the material properties of FG-CNTRC are varied through the thickness direction using four different distributions of carbon nanotubes (CNTs). In order to include the size effects in our modeling, the nonlocal elasticity theory presented by Eringen is utilized. The influences of different parameters such as volume fraction of carbon nanotubes, nonlocality and elastic foundation effects on the response of FG-CNTRC plates are studied. Numerical results prove high accuracy and reliability of the present method in comparison with other available numerical or analytical methods.
  • Investigating bulk metallic glasses as ball-and-cone locators for
           spacecraft deployable structures
    • Abstract: Publication date: Available online 4 October 2018Source: Aerospace Science and TechnologyAuthor(s): Douglas C. Hofmann, Punnathat Bordeenithikasem, Zachary Dawson, Lee Hamill, Robert P. Dillon, Bryan McEnerney, Steven Nutt, Samuel C. Bradford Ball-and-cone locators are the standard latching mechanism for spacecraft with deployable structures. Similar to other spacecraft components, the locators require the use of materials with low density and high performance. Bulk metallic glasses (BMGs) and their composites are alloys with superior mechanical properties with potential for spacecraft applications. In this study, Ti-based BMGs and their composites were prototyped for next-generation ball-and-cone locator inserts.
  • Investigations on the aerothermoelastic properties of composite laminated
           cylindrical shells with elastic boundaries in supersonic airflow based on
           the Rayleigh-Ritz method
    • Abstract: Publication date: Available online 2 October 2018Source: Aerospace Science and TechnologyAuthor(s): Yuyang Chai, Zhiguang Song, Fengming Li This paper is devoted to investigate the aerothermoelastic flutter and thermal buckling characteristics of composite laminated cylindrical shells with elastic boundary conditions. In the structural modeling, Donnell's shell theory is employed, and the supersonic piston theory is applied to evaluate the aerodynamic pressure. The elastic boundary constraints for the cylindrical shell are simulated by a series of distributed artificial springs. The shape functions of the laminated cylindrical shell with elastic boundary conditions are composed of characteristic orthogonal polynomials which are derived by the Rayleigh-Ritz method. The equation of motion of the structural system is established using Hamilton's principle. The high accuracy of the present method is verified by comparing the natural frequencies and flutter bounds with published results. Based on the frequency domain method, the aerothermoelastic properties of the laminated cylindrical shell with elastic boundary conditions are analyzed. The influences of different types of spring stiffnesses on the flutter and thermal buckling bounds are studied in detail. In addition, the influences of several parameters including the length to radius ratio, ply angle and boundary condition on the aerothermoelastic behaviors of the laminated cylindrical shell with elastic boundary conditions are researched.
  • Iterative Learning Control and Initial Value Estimation for Probe-Drogue
           Autonomous Aerial Refueling of UAVs
    • Abstract: Publication date: Available online 2 October 2018Source: Aerospace Science and TechnologyAuthor(s): Xunhua Dai, Quan Quan, Jinrui Ren, Kai-Yuan Cai In a probe-drogue aerial refueling system, the drogue is affected not only by wind disturbances but also by strong disturbances from the tanker vortex and receiver forebody bow wave. Along with the aerodynamic disturbances acting on the receiver aircraft, it is difficult for the probe to capture the moving drogue in the docking stage. This paper studies the model of the probe-drogue aerial refueling system under aerodynamic disturbances, and proposes docking control method based on iterative learning control to compensate for the docking errors caused by aerodynamic disturbances. For receiver aircraft with different maneuverability, three control strategies are proposed to achieve a trade-off between safety and control precision. Furthermore, a practical method is proposed to predict the initial value of the learning controllers, which can significantly improve the iterative learning speed of the proposed methods. Finally, simulations demonstrate that the proposed control methods are simple and efficient for the docking control of autonomous probe-drogue aerial refueling.
  • Buckling of spinning functionally graded graphene reinforced porous
           nanocomposite cylindrical shells: An analytical study
    • Abstract: Publication date: Available online 2 October 2018Source: Aerospace Science and TechnologyAuthor(s): Y.H. Dong, L.W. He, L. Wang, Y.H. Li, J. Yang This paper investigates the buckling behavior of functionally graded graphene reinforced porous nanocomposite cylindrical shells with spinning motion and subjected to a combined action of external axial compressive force and radial pressure. The weight fraction of graphene platelet (GPL) nanofillers and porosity coefficient are constant in each concentric cylindrical shell but vary layer-wise through the thickness direction, resulting in position-dependent elastic moduli, mass density and Poisson's ratio along the shell thickness. The first-order shear deformation theory incorporated with the von Kármán's geometrical nonlinearity is employed to describe the pre-buckling deformation. The governing equations of the cylindrical shell are established by using the minimum potential energy principle where the centrifugal effect due to the spinning motion of the cylindrical shell is considered. The pre-buckling deformation is derived by adopting the Galerkin method, then the axial critical buckling force, radial critical buckling pressure and critical buckling hydrostatic pressure are obtained with the effect of pre-buckling deformation being taken into account. Special attention is given to the effects of the porosity coefficient, the weight fraction, the dispersion pattern, the geometrical size of the GPL and spinning speed of the cylindrical shell on the pre-buckling deformation and different types of critical buckling loads of the porous nanocomposite cylindrical shell.
  • A survey on moving mass control technology
    • Abstract: Publication date: Available online 28 September 2018Source: Aerospace Science and TechnologyAuthor(s): Jianqing Li, Changsheng Gao, Chaoyong Li, Wuxing Jing Moving mass control is a control mechanism dedicated to regulating attitude of airborne vehicles by using motion of internal moving masses. This paper surveys the contemporary progress and problems of moving mass control technology in various capacities including spacecraft, spinning projectiles, underwater vehicles, unmanned aerial vehicles, and re-entry vehicles, special attention is paid to the moving mass configurations and its corresponding layout design methods. In addition, technological difficulties and developmental perspectives in dynamic analysis and attitude control problems of the underlying subject are also analyzed, and suggestions for future augmentation are proposed in the named field.
  • Experimental investigation of fuel composition and mix-enhancer effects on
           the performance of paraffin-based hybrid rocket motors
    • Abstract: Publication date: Available online 28 September 2018Source: Aerospace Science and TechnologyAuthor(s): Yi Wu, Xilong Yu, Xin Lin, Sen Li, Xiaolin Wei, Chuan Zhu, Linlin Wu Experimental investigations have been performed for a lab-scale hybrid rocket motor with hydrogen peroxide and paraffin-based propellants. A new paraffin-based solid fuel with favorable mechanical strength, consisting of 50 wt% paraffin, 20 wt% PE wax, 18 wt% EVA, 10 wt% SA and 2 wt% carbon, was proposed. The thermal properties of the proposed paraffin-based fuel and its components were firstly evaluated using TG/DTG measurements. It was found that the decomposition rates of each of the components of this paraffin-based fuel follow the order SA> pure paraffin> paraffin-based fuel blends> PE> EVA. Measurements of the regression rate of this paraffin-based fuel were performed and compared with results found in the literature. This showed that the regression rate of this paraffin-based fuel is much higher than that of traditional polymer solid fuels such as HTPB fuels. Finally, by adding a protrusion, a cavity and swirl blades at the end and in the middle of the combustion chamber, experimental investigations into the effects of a mix-enhancer on the paraffin-based hybrid rocket motor were performed. These investigations are discussed in detail.
  • Comprehensive Optimization of Aerodynamic Noise and Radar Stealth for
           Helicopter Rotor Based on Pareto Solution
    • Abstract: Publication date: Available online 28 September 2018Source: Aerospace Science and TechnologyAuthor(s): Zeyang Zhou, Jun Huang, Mingxu Yi To reduce the aerodynamic noise and radar cross section (RCS) of the helicopter rotor without sacrificing its aerodynamic characteristic, a comprehensive optimization method (COM) based on Pareto solutions is presented. An initial model of the rotor is created by full factorial design (FFD) and meshed by unstructured grid techniques to participate in the calculation and analysis of flow field and electromagnetic scattering field. The aerodynamic characteristics of the rotor flow field are simulated by computational fluid dynamics (CFD) method based on Navier–Stokes (N–S) equations and k–ε standard viscous model. According to the aerodynamic performance constraints of not reducing rotor lift, the thickness noise and the loading noise solved by Farassat 1A formula and the RCS value calculated by physical optics (PO) method and physical theory of diffraction (PTD) are designed as the comprehensive optimization goals. With the progress of the comprehensive balance analysis of these stealth indicators for the rotor models to be optimized, an excellent model with high comprehensive stealth performance and aerodynamic characteristic is generated by the proposed optimization method based on Pareto solutions. In addition, the effects of the models and parameters of each part of the rotor on these characteristics including aerodynamic lift, RCS, thickness noise and loading noise are analyzed in detail. It is effective and impactful of the comprehensive optimization method to deal with the multidisciplinary optimization problems of aerodynamic noise and radar stealth for helicopter rotor.
  • Differentiator based full-envelope adaptive control of air-breathing
           hypersonic vehicles
    • Abstract: Publication date: Available online 27 September 2018Source: Aerospace Science and TechnologyAuthor(s): Hao An, Qianqian Wu, Changhong Wang Despite the exciting improvement in air-breathing hypersonic vehicles (AHVs), most of the developed control strategies are only for cruise flight. This paper considers the longitudinal maneuver flight of AHVs, whose main purpose is to propose a low-dimension full-envelope adaptive control. In contrast to the existing adaptive back-stepping designs for AHVs, the proposed control synthetically handles the time-varying uncertain coefficients of aerodynamic force and moment that are inevitable during a full-envelope hypersonic flight, while accommodating actuator faults and flexible dynamics as well as circumventing over-parametrization and “explosion of complexity”. The above superiorities are attributed to the combination of the bound estimate mechanism and the sliding mode differentiator in a dynamic surface control scheme. The effectiveness of the proposed control is verified by a simulation study.
  • Finite-time sliding mode and super-twisting control of fighter aircraft
    • Abstract: Publication date: Available online 27 September 2018Source: Aerospace Science and TechnologyAuthor(s): Kaushik Raj, Venkatesan Muthukumar, Sahjendra N. Singh, Keum W. Lee The development of two nonlinear robust higher-order flight control systems for roll-coupled maneuvers of fighter aircraft with uncertain parameters is discussed in this article. The objective is to independently control the output variables (roll angle, pitch angle and sideslip angle), using aileron, elevator and rudder control surfaces. For a nominal model of aircraft, first, finite time stabilizing (FTS) control law based on the notion of geometric homogeneity is designed. Then, for robust control in the presence of parameter uncertainties, (i) a discontinuous sliding mode (DSM) control law and (ii) a super-twisting (STW) continuous control law is designed. It is shown that in the composite closed-loop system consisting of either (a) the FTS and DSM control laws or (b) the FTS and STW control systems, the output trajectory tracking error and its first-order derivative converge to the origin in finite time. Digital simulation results for a swept-wing fighter aircraft including the two composite control systems are obtained. These results show that each of the designed flight controllers accomplishes precise simultaneous large longitudinal and lateral maneuvers, despite uncertainties in the aerodynamic and inertia parameters, turbulence, and partial loss of control surface effectiveness.
  • Development of a Radiation Based Heat Model for Satellite Attitude
    • Abstract: Publication date: Available online 27 September 2018Source: Aerospace Science and TechnologyAuthor(s): A. Labibian, S.H. Pourtakdoust, A. Alikhani, H. Fourati This paper is focused on the development and verification of a heat attitude model (HAM) for satellite attitude determination. Within this context, the Sun and the Earth are considered as the main external sources of radiation that could effect the satellite surface temperature changes. Assuming that the satellite orbital position (navigational data) is known, the proposed HAM provides the satellite surface temperature with acceptable accuracy and also relates the net heat flux (NHF) of three orthogonal satellite surfaces to its attitude via the inertial to satellite transformation matrix. The proposed HAM simulation results are verified through comparison with commercial thermal analysis tools. The proposed HAM has been successfully utilized in some researches for attitude estimation, and further studies for practical implementations are still ongoing.
  • Characterization of induction and transition methods of oblique detonation
           waves over dual-angle wedge
    • Abstract: Publication date: Available online 27 September 2018Source: Aerospace Science and TechnologyAuthor(s): Bikalpa Bomjan, Sudip Bhattrai, Hao Tang The oblique detonation wave (ODW) induction and initiation lengths can be reduced significantly by the use of a dual-angle wedge with two subsequent, high and low, angles. In this study, the dual-angle wedge is deflected to different angles at different positions along the wedge and the resulting effects on the shock-to-detonation transition are observed. One-dimensional analytical modeling of flow conservation equations with finite-rate multi-step reaction is carried-out to obtain reactive flow properties over plain and dual-angle wedges. Numerical study was carried out in OpenFOAM to observe the induction and shock-to-detonation transition characteristics. Two different transition mechanisms were observed over dual-angle wedges. The first is an abrupt-type transition from an oblique shock wave (OSW). While the second mechanism involves a brief induction process followed by an intermediate span of shock-induced combustion, which leads to a smooth transition into an ODW. The ODW is formed over the second wedge-angle in both cases. The ODW induction and initiation lengths can be reduced significantly by initially inclining the wedge at a higher angle over only a very short span of the wedge. The second wedge-angle primarily affects the ODW initiation length and downstream flow properties. The position of wedge deflection was identified as a critical geometric parameter which can affect the ODW induction, transition and formation properties.
  • Experimental study of stall control over an airfoil with dual excitation
           of separated shear layers
    • Abstract: Publication date: Available online 26 September 2018Source: Aerospace Science and TechnologyAuthor(s): Abbas Ebrahimi, Majid Hajipour, Kamran Ghamkhar This paper investigates the stall control over an airfoil employing dual excitation of separated shear layers with dielectric barrier discharge plasma actuators. This novel approach is studied experimentally on the NACA 0015 airfoil at the angle of attack and Reynolds number of 14° and 0.3×106, respectively. To analyze the baseline flow, Time-averaged pressure distributions on the airfoil surfaces are evaluated with 40 pressure taps. Further, the dominant natural frequencies associated with flow structures in the airfoil wake are examined utilizing a hot-wire anemometer. Two plasma actuators, one on the suction side just upstream the separation point and the other on the pressure side at the trailing edge, are exploited to control the baseline flow. Based on the active actuators, three controlled cases are considered in the present study. In the first case, the frequency of natural vortex shedding and its different harmonics are employed to excite the suction side separated shear layer. In the second case, plasma actuation is applied to the shear layer at the trailing edge. Further, in the third case, both of the actuators are utilized to excite the separated shear layers on the suction side and the trailing edge, simultaneously. The results of the pressure coefficient distributions, as well as the aerodynamic coefficients, are compared for all cases. Moreover, the actuators energy consumption is evaluated for the controlled cases and a new efficiency parameter is presented. Accordingly, the first case prevents the stall phenomena only at the wake mode frequency and its first super-harmonic. In addition, using the plasma actuator at the trailing edge solely is an ineffective flow separation control strategy. However, dual excitation is promising for a full stall control in a wide range of excitation frequencies. Analyses of the lift-to-drag ratio and the efficiency parameter reveal that the dual excitation case is the most efficient stall control technique.
  • Influence of fillet shapes on secondary flow field in a transonic axial
           flow turbine stage
    • Abstract: Publication date: Available online 25 September 2018Source: Aerospace Science and TechnologyAuthor(s): K. Ananthakrishnan, M. Govardhan Numerical experiments were conducted to investigate the effect of leading edge modifications via fillet shapes near vane/blade-endwall juncture in a transonic environment within the highly loaded high pressure turbine stage. The investigated fillet shapes were designed based on geometric parameters: leading edge radius and included angle. The geometrical modifications were achieved to achieve variation in fillet radii at vane/blade endwall juncture along the stream-wise direction, namely variable fillet and constant fillet. Further their influences were studied in both nozzle guide vane and rotor passage secondary flow field. Computational Fluid Dynamics (CFD) method was used to resolve the flow features inside the turbine passage for planar and fillet cases. The presented data highlight the secondary flow features and their behavior using topological properties of flow field aided with the streamline and iso-contour plots. The flow-field results show a significant reduction in the total pressure losses associated with the horse shoe vortex near the leading edge region as the fillet radii are varied. Overall in both vane and rotor passages, variable fillet outperforms the constant fillet by reducing the penetration length of three-dimensional regimes along its span, mitigating the boundary layer growth and improving the loss coefficients.
  • Instability detection of centrifugal compressors by means of acoustic
    • Abstract: Publication date: Available online 25 September 2018Source: Aerospace Science and TechnologyAuthor(s): Zhenzhong Sun, Wangzhi Zou, Xinqian Zheng Preventing the compressor from instability phenomena is of great importance for the safe operation of many industrial products, such as aero-engines. Hence, a simple and low-cost method is extremely demanded to detect instability phenomena of compressors, especially in the real operating environment, and acoustic measurement is an alternative solution. In this paper, dynamic pressure and acoustic characteristic of a centrifugal compressor are experimentally investigated. First, all typical operation conditions of the compressor are illustrated and all instability phenomena that occur within the compressor are identified. Then, dynamic pressure is analyzed to present characteristics of different instability phenomena. Finally, the ability of acoustic measurement to detect instability phenomena is discussed with detailed analysis on acoustic signals, and guidelines for instability detection by means of acoustic measurement are established. Results show that four instability phenomena, rotating instability, rotating stall, mild surge and deep surge, occur within the compressor. In addition, the acoustic sensor is recommended to be installed near the compressor casing, and the acoustic signal can detect the rotating stall, the mild surge and the deep surge by capturing their characteristic frequency. This paper demonstrates the ability to capture instability phenomena via acoustic signals and provides an acoustic measurement technology to detect instabilities at any time of the full life cycle of a compressor.
  • Heat transfer aspects of regenerative-cooling in methane-based propulsion
    • Abstract: Publication date: Available online 25 September 2018Source: Aerospace Science and TechnologyAuthor(s): Maryam Shokri, Abbas Ebrahimi In the present article, thermal behavior and heat transfer deterioration (HTD) of transcritical methane as well as the fluid state change in regenerative cooling with straight/curved rectangular channels are studied numerically. Simulations are conducted with a finite-volume based CFD solver utilizing reliable turbulence models and thermo-fluidic relations in transcritical conditions. The experimental and numerical results of hydrogen inside a heated tube in the literature are used for validation. The effects of mass flow rate, outlet pressure, wall temperature, surface roughness, and the channel geometry on the thermal behavior of the coolant fluid are studied in detail. According to the results, variations in the slope of the transport property curves and the inflection point in the density distribution of the coolant flow are proposed as criteria for the recognition of the HTD and transcritical regions, respectively. In addition, the outlet pressure and surface roughness have negligible effects on both methane HTD and transcritical regions in contrast to the channel curvature, mass flow rate, and wall temperature.
  • Onboard Trajectory Generation for Gyroplane Unpowered Landing Based on
           Optimal Lift-to-Drag Ratio Target
    • Abstract: Publication date: Available online 24 September 2018Source: Aerospace Science and TechnologyAuthor(s): Xiaoxing Fang, Yingxun Wang, René Landry To achieve the autonomous unpowered landing for gyroplanes, an onboard trajectory generation method is presented in this paper. As a pivotal variable in the proposed method, the Lift-to-Drag Ratio will be uniquely determined in different phases by finding the maximum for the energy margin during approaching and the energy decrease at terminal landing. Especially, autorotation constraint, the primary requirement of gyroplanes for flight stability, has been considered as a limitation factor through this procedure. Furthermore, a geometrically constrained three-dimensional trajectory profile is employed, in which a multi-circle Heading Align Cone is proposed to improve its applicability. Accordingly, a predictor-corrector algorithm is derived and described for trajectory generation with initial variance and terminal requirements. Employing the algorithm onboard, by adjusting few geometric parameters dynamically, a feasible trajectory reference that meets the specified constraints can be generated efficiently. Results from numerical calculation and closed-loop simulation under different scenarios demonstrate the effectiveness and robustness of the approach.
  • Probabilistic Aircraft Trajectory Prediction in Cruise Flight Considering
           Ensemble Wind Forecasts
    • Abstract: Publication date: Available online 24 September 2018Source: Aerospace Science and TechnologyAuthor(s): Antonio Franco, Damián Rivas, Alfonso Valenzuela The problem of aircraft trajectory prediction subject to wind uncertainty is addressed. In particular, a probabilistic analysis of aircraft flight time and fuel consumption in cruise flight is presented. The wind uncertainty is obtained from ensemble weather forecasts. The cruise is composed of a given number of segments subject to uncertain winds (both along-track winds and crosswinds). The resulting average ground speed of each segment is modeled as a random variable, assuming a Log-Normal distribution. The probabilistic trajectory predictor developed is based on the Probabilistic Transformation Method; the input is the probability density functions of the average ground speeds of the cruise segments, and the output is the probability density functions of the flight time and the fuel consumption. Results are presented for several aircraft of different categories (medium and heavy), for a given trans-oceanic route and a real ensemble weather forecast. The effects of wind uncertainty on flight predictability and on fuel loading are analyzed. A fuel penalty parameter is defined, and the cost of flight unpredictability is quantified. The sample variability of all the results has been quantified by means of standard errors.
  • H ∞ output trackingcontrol of Electric -motor-driven aerodynamic Load
           Simulator with external active motion disturbance and nonlinearity
    • Abstract: Publication date: Available online 24 September 2018Source: Aerospace Science and TechnologyAuthor(s): Chengcheng Li, Yuefeng Li, Guanglin Wang The work presented in this paper seeks to address the tracking problem foranElectric-motor-drivenaerodynamic Load Simulator(ELS).The tracking performance of ELS is mainly affected by the actuator'sactive motion disturbance, friction nonlinear, and parametric uncertainties.Most of the previous studies onELSfocus on the actuator's active motion disturbance, while deemphasizing the othertwo factors.This paper concerns ELS as a motion loading system. A new high performancecontrol scheme is developed to deal with the three factors based on the established nonlinear mode of ELS. The control scheme is based on neural networks andthe Linear Difference Inclusions(LDI)model.Aparallel distributed compensation(PDC) structureand H∞ performance criterion are used to attenuate external disturbances.The stabilityof the whole closed-loop model is investigated using the well-known quadratic Lyapunovfunction.Both asimulationand anexperiment are performed to validate the effectiveness of the developed algorithm.
  • Unsteady effects of vortex interaction on tip leakage vortex breakdown and
           its loss mechanism
    • Abstract: Publication date: Available online 24 September 2018Source: Aerospace Science and TechnologyAuthor(s): Kai Zhou, Chao Zhou In an unshrouded high-pressure turbine, tip leakage flow causes a loss of efficiency. The loss mechanisms of tip leakage flow were investigated mostly with steady uniform incoming conditions in previous studies. This paper investigated the unsteady aerodynamic performance of the tip leakage flow in a turbine stage by solving Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations. The unsteady results were also compared with results obtained by the steady simulation. Cases without rotor tip clearances were simulated to estimate the entropy generation due to the tip leakage flows.In the steady calculation, tip leakage vortex breakdown occurs due to its strong streamwise vorticity. Large entropy loss is generated due to vortex breakdown. Caused by blade rotation, the unsteady stator passage vortex evolution through the rotor passage was clearly unveiled. The enhanced stator passage vortex periodically interacted with the flow near the rotor tip and reduced the vorticity magnitude of tip leakage vortex. As a result, the vortex interaction periodically suppresses this vortex breakdown, thus reducing the loss. In the steady simulation, the axial length of tip leakage vortex breakdown is about 25% chord. However, in the unsteady simulation, the minimum axial length of the breakdown vortex is 10% chord. The entropy due to the tip leakage flow is evaluated in both the steady simulation and unsteady simulation. The time-averaged entropy generation of unsteady tip leakage vortex is 18% less than the loss in the steady case, which implies that unsteady vortex interaction improves the aerodynamic performance of tip leakage flow.
  • Sizing of Hybrid Electric Propulsion System for Retrofitting a Mid-Scale
           Aircraft Using Non-dominated Sorting Genetic Algorithm
    • Abstract: Publication date: Available online 24 September 2018Source: Aerospace Science and TechnologyAuthor(s): Ye Xie, Al Savvaris, Antonios Tsourdos The paper presents the sizing of a hybrid electric propulsion system for a prototype aircraft. The main contribution of the paper is to apply multi-objective optimization in the retrofit of a mid-scale aircraft and investigate the fuel economy of the hybrid aircraft for a particular mission cycle. Using the Non-dominated Sorting Genetic Algorithm (NSGA), the fuel consumptions for different flight durations are minimized, which represent the optimal trade-off between fuel consumption and flight duration. With no compromise on endurance and range, the maximum fuel reduction of the retrofitted hybrid aircraft reaches 17.6%, by comparison with the prototype aircraft. The retrofitted aircraft achieves better cruising and climbing performance with the sized hybrid propulsion system. The novelty of the study is the proposal of a new non-dominated sorting algorithm—Benchmark based Non-Dominated Sort (BNDS) for the NSGA. BNDS can reduce the number of comparisons and the time complexity of the non-dominated sorting process. A constraint handling approach is also integrated into the BNDS/NSGA to address performance and mission requirements.
  • Quasi-3D higher-order shear deformation theory for thermal buckling
           analysis of FGM plates based on a meshless method
    • Abstract: Publication date: Available online 21 September 2018Source: Aerospace Science and TechnologyAuthor(s): Vuong Nguyen Van Do, Chin-Hyung Lee This study introduces a new quasi-3D (three-dimensional) higher-order shear deformation theory (HSDT) capable of accounting for the through-thickness deformations with only four unknowns, which is suited to the numerical method for buckling analysis of functionally graded material (FGM) plates in thermal environments. The refined quasi-3D HSDT is incorporated into the improved meshless radial point interpolation method (RPIM) in order to scrutinize the thermal buckling responses of FGM plates. In the improved RPIM, the radial basis function is presented in a compactly supported form to build the shape functions without any fitting parameters. Parametric studies on the buckling behavior of FGM plates under various types of through-thickness temperature changes are conducted and the effects of temperature distribution on the plate surface are investigated. Results illustrate the accuracy of the proposed meshless method based on the refined quasi-3D HSDT and the improved RPIM for predicting the thermal buckling behavior of FGM plates.
  • Experiment and analysis on radiation properties of SiO
    • Abstract: Publication date: Available online 18 September 2018Source: Aerospace Science and TechnologyAuthor(s): C. Sun, H.F. Sun, Z.Y. Wang, X.L. Xia The thermal control coatings (TCC) on the surfaces of lunar rover/landers plays an important role for radiation heat transfer to allow the detectors survive the extremely critical thermal environment on the moon. Optical Solar Reflector (OSR) coating is usually considered as a good candidate TCC due to its excellent radiation properties such as low solar absorptance and high infrared emittance. In this study, SiO2/Ag coating, commonly used as OSR, was investigated to study its radiation properties, combining experiment measurement with numerical simulations. Based on the self-made setup with the comparison method, the temperature dependence of the normal infrared emittance of the OSR coating was obtained, covering the temperature range from 326 K to 404 K, to simulate the temperature condition on the Moon in the daytime. The direction hemisphere spectral reflectance at the typical wavelength of 0.6328 μm, 1.34 μm and 3.39 μm was also investigated in details. It was found that the spectral reflectance of the OSR coating at visible wavelengths is much higher than that at infrared wavelengths. In addition, numerical simulation result showed good agreement with the experimental data, and the relative error is 4.49% at 0.6328 μm.
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