Journal of Aerospace Engineering

The fiber architectures of the stomatopod dactyl club lead to an effective toughening mechanism. Composites with sinusoidally periodic helicoidal (Herringbone-type) fiber architectures were fabricated using additive manufacturing and examined under dynamic loading. Under compression at different strain rates, stress distribution was found more uniform in the Herringbone-type structure than that in the Bouligand-type one because of fiber flattening. Under dynamic compression, Herringbone-type structures with amplitude gradients resisted large strains without significant damage, leading to greater energy absorption. Simulations indicated that the Herringbone-type structure mitigated the impact waves and facilitated uniform stress redistribution, whereas the Bouligand-type structure filtered the waves. These findings would shed light on the future designs of impact-resistant bioinspired materials.

In this paper, the finite-element (FE) method combined with smoothed particle hydrodynamic (SPH) method is used to simulate the bird strike process, and a new type of tail leading edge structure is designed. This kind of bird is represented by the SPH model, and the structure is simulated by traditional Lagrangian elements. The design for the novel structure can be described as incorporating a triangular reinforcement component into traditional tail leading edge structure. Numerical simulations of bird strikes with the novel structure indicate that the anti-bird-strike capacity of the new type of tail leading edge is greatly enhanced. Then, the corresponding bird strike tests are carried out to verify the numerical simulation model. The simulation results are in good agreement with the test results, indicating that the SPH-FE coupling method gives a useful tool for predicting the deformation and damage behavior of aircraft structure under bird impact, and for the design of bird-strike-resistant structure. Finally, through bird strike simulation and test of the horizontal tail leading edge with the new design of commercial aircraft, it can be observed that the front beam does not penetrate, which indicates that the new design meets the requirements of the China Civil Aviation Regulations (CCAR) Part 25 on the certification of the bird strike resistance of the wing leading edge.

This paper focuses on a single-axis control of a wheeled spin satellite while the entire angular momentum is not zero. The presented technique includes a feedback control law that asymptotically and globally stabilizes the satellite along a desired inertial direction despite external disturbances, actuator constraints, and a significant cross-product of inertia. Simulations for three possible geometrical configurations of a control system based on two reaction wheels were carried out to verify the presented control algorithms. In the three presented scenarios, the wheel of the controlled axis was removed, which means that in the case of having three reaction wheels, spinning the satellite about all axes is possible. It is shown that the harmonic motion of wheels can be disappeared using only one magnetic torquer aligned with the wheelless axis. Simulation and air bearing testing results show that the control system can produce successful rapid spin axis reorientation using reaction wheels.

This paper presents detailed mathematical modeling, controller design, and flight test results for the autonomous mission of a nonconventional fixed-wing biplane micro air vehicle (MAV) called Skylark having span and chord length within 150 mm. Although numerous fixed-wing MAV designs are reported in the open literature, an MAV’s reliable autonomous flight is still a challenge. The primary difficulties in performing the autonomous mission of fixed-wing MAV are system integration within the weight and power budget, center of gravity (CG) management, and flight controller design for fast dynamics. In this paper, the key challenges are addressed by using the higher payload capacity of Skylark, suitable selection and design of avionics components, and design of controller after detailed development of the mathematical model, including the additional effect of propeller wash and motor countertorque. An autonomous flight test is successfully demonstrated after the validation of algorithms and software architecture through nonlinear six-degrees-of-freedom simulation. The detailed design and development approach will increase the MAV’s performance and reliability in civil and military applications.

In recent years, the Kalman filter based on the minimum error entropy (MEE) criterion has been proposed, which outperforms the traditional Kalman filter in the presence of non-Gaussian noise. In practical applications, the estimated performance of the MEE unscented Kalman filter (MEE-UKF) algorithm is influenced by the kernel bandwidth (KB). In addition, it may be unstable in numerical computation. This paper proposes an adaptive robust MEE unscented Kalman filter (AMEE-UKF) to address the problem of instability in numerical computation. In addition, by setting an adaptive factor to optimize the MEE-UKF, an appropriate value of the KB can be obtained adaptively. The high accuracy and robustness of the AMEE-UKF were demonstrated by the simulation experiments.

Low-frequency errors are a type of testing errors commonly existing in pyroshock experiments due to the harsh mechanical environment that lead to inaccuracy and contamination of pyroshock data. It is necessary to eliminate such low-frequency errors from pyroshock data via data analysis. Two methods based on discrete wavelet transform (DWT) and ensemble empirical mode decomposition (EEMD) are proposed, respectively, in this article. Firstly, the principle and operating process of these two methods are introduced, where four correlation coefficients are defined to determine the decomposition level for quantitative correction. Then, the two methods are applied to remove the integral zero shift from a set of pyroshock test data, respectively, and the capability and effectiveness of the two methods are compared. It is revealed from the comparison studies that both methods are capable of removing integral zero shift effectively to correct the shock response spectrum and improve the accuracy of pyroshock data. The correlation coefficients constructed here can help to realize quantitative selection of key parameters for the two methods. The DWT method shows better correction performance for extracting accurate parameters, whereas the EEMD method is more concise and convenient for application.

This study examines two techniques to optimize the design of lightweight composite IsoTruss columns subject to uniaxial compression: gradient-based (interior-point with algorithmic differentiation and Latin hypercube sampling) and gradient-free (nonsorting genetic algorithm). Both methods used analytical expressions to minimize mass with respect to the number of bays, number of carbon tows in each longitudinal member, and the outer diameter. The general geometric configuration was based on experimental specimens, tested previously, that were approximately 3 m (10 ft) long and 0.14 kg (0.3 lb). The analytical constraint functions used to predict material failure and buckling were verified by finite-element analysis and validated with experimental data in preceding works. The gradient-based and gradient-free approaches both produced similar results, indicating an optimal design 14%–16% lighter than the experimental configuration used as the initial design criteria. Sensitivity derivatives produced in the gradient-based analysis indicated that (1) increasing any of the design variables increases the mass of the structure; (2) increasing the outer diameter increases the global buckling capacity and decreases the shell-like buckling capacity; (3) increasing the number of bays increases the local buckling capacity with negligible impact on the global buckling capacity; and (4) increasing the number of tows in each longitudinal member increases both the global and local buckling capacities. Although both methods produced similar results and demonstrated satisfactory convergence, the gradient-based framework was selected for a subsequent study to evaluate novel IsoTruss configurations because it provides additional insights to the design space via outputs such as Lagrange multipliers and Jacobian matrices. The gradient-free framework could be augmented and used in future studies to optimize IsoTruss structures for specific applications and design criteria.

In this paper, higher-order dynamic mode decomposition (HODMD) was applied to find the main patterns and frequencies of a transient aerodynamic flow field when an aircraft wing experiences stall. This method was applied to a computational flow simulation with a turbulence model based on a hybrid Reynolds-averaged Navier-Stokes large-eddy simulation (RANS/LES) [commonly known as detached-eddy simulation (DES)], where a combination of two-dimensional (2D) and three-dimensional (3D) flow visualization techniques are used to understand the vortex shedding from the main wing and its interaction with the tailplane. Simulation results were compared to the experimental ones and the results with proper orthogonal decomposition (POD) were compared with the HODMD analysis. The main advantage of HODMD resides in its identification of the main physical phenomena and the most relevant instabilities that lead the fluid dynamics. New flow control strategies can be defined when the underlying physics and the flow dynamics are known. Moreover, HODMD is robust in noisy and turbulent databases using less data than fast Fourier transform (FFT), which gives potential for future flow control applications, focused on improving the aircraft’s efficiency.

Strong coupling of aerodynamics and dynamic motion will occur on advanced highly maneuverable aircraft at a high angle of attack, which makes the complex flow field heavily nonlinear. To improve the aerodynamic performance at a high angle of attack and broaden the flight boundary of the aircraft, a new combination configuration of a prepositive elliptical wing–main wing is proposed. The high-energy wake vortex generated by the stationary or vibrating prepositive wing is mixed with the airflow field of the main wing at the high angle of attack, and the air flow is accelerated through the space between the elliptical wing and its main wing, thereby enhancing the ability of the boundary layer to resist separation. A two-dimensional combined configuration of a stationary or vibrating prepositive elliptical NACA0012 airfoil was designed, and the flow control simulation was studied with a high-precision computational fluid dynamics (CFD) method. The results show that the stationary elliptical wing generates lift by itself, the generated wake suppresses the flow separation on the upper wing surface of the main wing, and the lift-to-drag ratio can be increased by as much as 319%. Moreover, when the prepositive wing vibrates at a small amplitude, the generated wake energy is stronger and the control effect on the separation of the main wing is much more remarkable. In the best case, the lift-to-drag ratio of the main wing can be increased by 485%. Compared with conventional flow control techniques, the new combined flow control method has the characteristics of a simple form and a high degree of control without forming waste resistance, and significantly can improve the flow separation characteristics at high angles of attack and enhance the maneuvering ability of aircraft.

In this paper, an integrated tracking control approach was developed for a continuum robot in space capture missions. For the configuration of a three-module cable-driven continuum robot, the nonlinear dynamics equations were derived. The uncertain movement of noncooperative debris requires a real-time trajectory planning solution. Therefore, an adaptive controller based on deep reinforcement learning (DRL) is proposed to generate a dynamic controller in continuous action space, where the trajectory planning function is simultaneously integrated into the dynamic solution. To obtain an efficient policy network for the highly nonlinear dynamics model, the rolling optimization method was combined in the DRL method of the deep deterministic policy gradient (DDPG). The DRL controller generated an appropriate control sequence according to the long-term control performance of the robot system and then executed optimal control input according to the rolling optimization. The simulation result shows that the proposed policy network of the improved DDPG controller can reasonably provide the tracking control solution in the noncooperative debris capture mission.

This paper proposes a new method to solve Lambert’s problem with multiple constraints, including the impulse-magnitude constraints, the trajectory-radius constraints, and the terminal-impact-angle constraint. First, the closed-form range of the chordal terminal velocity component for each constraint is derived. Then, the admissible intersection range for all constraints is obtained. Finally, the feasible solutions are solved in the admissible intersection range by using the terminal-velocity-based Lambert algorithm. The 180° case and the multiple-revolution case are also considered. The proposed method can be also extended to the Lambert algorithms with other independent variables. Compared with the typical method of first solving Lambert’s problem and then pruning the solutions that do not satisfy the constraints, the numerical examples show that the proposed method can reduce a lot of computational time.

In this paper, four types of truss lattices are designed by combining octet truss (FCC) unit cells with other elementary unit cells, including Simple Cubic (SC), Body-centered Cubic (BCC), Body-centered Block (BCB), and Z-pinned (Z). The elastic properties (uniaxial, shear, and bulk moduli, Zener’s anisotropy index, and Poisson’s ratio), yield strength, deformation modes, and energy absorption under quasi-static loading, and impact resistance under dynamic loading of these lattices were investigated through finite elements. The initial peak stress and subsequent plateau stress are elevated under dynamic loading. The stress waves velocity of the lattices is calculated by the dynamic enhancement term. Results indicate that the mechanical properties of the designed lattices are better than the reported FCC and BCC lattices. FCCBCB (which is combined with FCC and BCB elementary unit cell) remains stable for uniaxial compression at a relative density of about 0.2 and exhibits the highest energy absorption capacity at the relative density considered; the Zener index of FCCSC (which is combined with FCC and SC elementary unit cell) does not vary greatly with the increase of relative density (1.18 to 1.11 at the relative density considered), and the Zener index approaches unity indicating elastic isotropy; and FCCZ (which is combined with FCC and Z elementary unit cell) features the highest yield strength and Young’ modulus among all lattices considered. The computational results are confirmed through uniaxial compression experiments on three-dimensional (3D)-printed specimens.

During soft landing on asteroids, the weak gravity and rugged terrain put the spacecraft at risk of crashing and bouncing, such that a safe and accurate landing is essential for the spacecraft. In this paper, a new flexible spacecraft, composed of three thrust units and connecting airbags, is designed for asteroid landing. To estimate the flexible deformation of the spacecraft, an equivalent system model consisting of three spring-damping components and three thrust units is developed. Based on this model, a control scheme including path planning, tracking control, and control allocation is proposed. Considering double-zero constraints and flexible connection constraints, the trajectories of three thrust units are planned with the Gaussian pseudospectral method and then fitted into the trajectory of the flexible spacecraft mass center. Then, a nonsingular terminal sliding mode control law considering flexible body disturbances and thruster saturation problems is designed. To solve the control allocation problem, an active set algorithm considering the time-varying installation matrix caused by the flexible deformation is applied. Two simulation cases are provided to demonstrate the effectiveness of the proposed control scheme.

To reduce the sensitivity of trajectory to uncertainty, this paper concerns the robust trajectory optimization of the solid ascent launch vehicles with the uncertainty of aerodynamic parameters and engine mass flow. Due to the strong nonlinearity and fast time-varying characteristics, the traditional robust trajectory optimization method based on polynomial chaos expansion (PCE) has slow convergence speed and large prediction errors. To overcome these difficulties, an improved robust optimization algorithm based on sample updating and adaptive truncated PCE (UAPCE) is put forward. Compared with the conventional PCE optimization methods, our contributions mainly focus on three aspects: First, to optimize the standard deviation of the terminal trajectory under uncertainty conditions, the original state is sampled and expanded by PCE, and the statistical characteristics of the original state, constraints, and indicators are described by the expanded state. Second, in order to promote the convergence speed of PCE, the sampling points are updated automatically by the proposed sample updating method in the pseudo-spectral optimization of the expanded state. Finally, the adaptive polynomial truncation method is creatively proposed to break through the fitting accuracy limit of the conventional PCE method under the same computation complexity. Through Monte Carlo simulations, the proposed UAPCE greatly reduces the standard deviation of the terminal state compared with the nonrobust optimization, demonstrating strong robustness to the uncertainty. Simultaneously, the UAPCE method has better convergence speed and prediction accuracy compared with the traditional PCE method.

Abstract

To develop an efficient hypersonic diffuser, a numerical investigation was performed on a center-body diffuser and a second-throat cylindrical diffuser of a large-scale arc-heated wind tunnel with a Mach number 6 nozzle. The length of the diffuser was set to 16 m, and the total pressure and temperature were over 28 atm (2,837 kPa) and 2,000 K to simulate a 13-MW wind tunnel. The ARCFLO4 code was used for the investigation and flow analysis, with air as the working gas inside the wind tunnel, assumed to be in thermal and chemical equilibrium. The axisymmetric Reynolds-averaged Navier-Stokes equation was used as the governing equation. The flow structure and characteristics inside each diffuser were analyzed and compared, and a novel diffuser shape locating a center body in the subsonic region was proposed to compensate for the disadvantages of each diffuser. Moreover, the performance of each diffuser was evaluated based on the maximum efficiency, cooling effect, and exit velocity. The proposed diffuser showed the lowest exit temperature, enthalpy, and velocity with high efficiency; therefore, the proposed diffuser is expected to reduce the cost of wind tunnel installation and operation, alleviating the requirements of the heat exchanger or vacuum chamber.

Abstract

By performing a numerical investigation on general diffuser types of a high-enthalpy wind tunnel, a novel diffuser is introduced here that can lower the exit velocity, temperature, and enthalpy of the internal flow. The proposed diffuser has a center body with a cooling system in the subsonic flow region to minimize the total pressure loss and reduce flow velocity and temperature. In particular, it is effective in reducing the elevated flow temperature due to the shock wave of the supersonic flow. This study is applicable to not only the diffuser but also pipe flow; kinetic energy loss may occur due to the center body by reducing effective area, but the efficiency of the device is almost maintained, but the temperature and enthalpy of the flow are reduced. By adding a center body, it is possible to design and manufacture an efficient new device; further, it may have the advantages of extending the operating range to an existing device by adding a center body.

Abstract

Plasma synthetic jets (PSJs) have received widespread attention because of their rapid response capability. The use of PSJ shock and thermal effects for active flow control has been investigated in many recent studies. Through numerical simulation, this study found that the geometric position of a PSJ actuator on an airfoil surface is the key factor affecting flow control effects. Different geometric positions have different effects on the lift-drag characteristics of an airfoil, and the flow control mechanism has different components. The flow control mechanism can be divided into three types: the thermal effect, the coupling of the thermal effect and single shock, and the coupling of thermal effect and multiple-shock rebound. The concept of distance $l_{\mathrm{placement}}$ provides a reference for determining the geometric arrangement of a PSJ actuator. This study showed that in addition to improving the lift-drag characteristics of an airfoil by reducing drag, directly increasing lift is also a new choice. In addition, in a confirmatory experiment, the nanosecond pulse PSJ actuator pushed the bow shock in a Mach 5 flow; the longest distance was about 1% of the characteristic length of the airfoil.

Practical Applications

In this work, a new type of plasma actuator was used for flow control in hypersonic flow. The influence of the geometric position of the actuator on flow control and the corresponding flow control mechanisms were investigated. This work provide a reference for most work using actuators. For example, the geometric position of an actuator can be selected according to $l_{\mathrm{placement}}$ defined in this work and the parameters of the actuator can be set according to the parameter settings of the PSJA. For aerodynamics research, this work provides a new research idea for improving the aerodynamic performance of aircraft. If drag reduction is difficult to achieve, then increasing lift is also a feasible method. For research on plasma flow control, this work broadens its application to hypersonic flow and reveals that a plasma actuator has two flow control effects at the same time. PSJA conducts flow control through the impact effect of the diffracted wave and the mixing effect of the high-temperature cluster; this provides a reference for relevant personnel.

The formation of a laminar separation bubble (LSB) at low Reynolds numbers has a significant impact on the aerodynamic performance of an airfoil. An experimental study was conducted to investigate the feasibility of using an intermittent disturbance control method to maintain the stability of this LSB, aiming to suppress the flow separation on a National Advisory Committee for Aeronautics (NACA) 633-421 airfoil model at a low Reynolds ($Re$) number. The dynamic bursting process of the LSB at $\alpha =10°$ and $Re=1.2\times {10}^5$ was reproduced using this flow-control method. During the experiments, dynamic pressure measurements and particle image velocimetry were used to examine the upper-surface pressure distribution and partial flow field of the airfoil model, respectively. It was found that during the bursting process, the LSB could naturally exist for an initial short time period, defined as $T_{\mathrm{maintain}}$, and the laminar separated shear layer kept moving away from the surface, leading to bursting of the LSB as well as a stall. By making use of $T_{\mathrm{maintain}}$, an interval time for the disturbances, $T_{\mathrm{int}}$, was roughly determined and used as the control period for flow disturbances produced from synthetic jet actuators. This intermittent disturbance can interrupt the further development of the natural bursting process of the LSB and trigger a cycle of rebirth of the LSB, forming a stable LSB on the airfoil. A power spectrum of the dynamic pressure measurements at the reattachment point showed that the intermittent frequency dominated the reattachment frequency of the separated shear layer.

Topology optimization studies have found widespread use with advances in additive manufacturing technologies. A topology optimization method is proposed for the design of a fatigue critical part, namely, a pitch arm made of Al 7050, which transmits the commands to change the pitch attitude to the rotor blades of the helicopter. This study used the bidirectional evolutionary structural optimization (BESO) method with the fatigue failure criterion of a closed Soderberg (CS). The mean stress and stress amplitude values used in the procedure were obtained by applying the Manson-McKnight method. The calculations were performed using a Python-based script compatible with Ansys version 2021 R1 software. In the finite-element calculations, the sensitivity number of the elements was determined using the results of the linear static analysis. A volume constraint was applied in the formulation of the optimization problem to minimize the weight of the structure. The results of the classical topology optimization approach and the developed optimization method were compared. The final geometries of both approaches showed that the ranges of volume reduction differed from each other. It was found that the values for the new fatigue-optimized weight of the pitch arm were 18% higher than the values for the static-based classical topology optimization method. However, in general, the weight of the part obtained as a result of fatigue-based topology optimization was reduced by 34% in total.

The linear and non-linear thermal stability characteristics of three-phase randomly distributed carbon nanotube (CNT)–reinforced fiber composite (RD-CNTRFC) shell panels are explored in the present study. Nonlinear kinematics for shell panels are expressed based on higher-order shear deformation theory (HSDT) and von-Kármán non-linearity. Effective properties of the RD-CNTRFC are computed in two stages: The first stage estimates the effective properties of the matrix reinforced with randomly distributed carbon nanotubes (i.e., hybrid matrix) using the Eshelby-Mori-Tanaka approach, and the second stage estimates the effective properties of a hybrid matrix reinforced with unidirectional fibers by adopting various homogenization techniques. Effective material properties of composite are considered to be temperature-dependent. Hamilton’s principle is employed to derive the governing partial differential equations (PDEs) by utilizing kinematic and constitutive model of the RD-CNTRFC shell panels. Then, Galerkin’s method reduces the PDEs into nonlinear algebraic equations. An iterative eigenvalue approach is used to estimate the stability characteristics of the RD-CNTRFC panels. The present investigation is initially verified by comparison with published results. Next, numerical results are presented in detail to understand the influence of CNT agglomeration, temperature-dependent properties, mass fraction, aspect ratio, and ply sequences on the thermal stability characteristics.

Adhesively bonded joints are widely preferred for joining similar and dissimilar materials due to the mechanical advantages they provide. As the demand for the adhesively bonded method increases, it is necessary to determine the behavior of joints under impact loads for joint design. The aim of this study was to investigate the low-speed oblique impact behavior of dissimilar single-lap joints and the effect of plastic deformation ability and strength of the adherends [(Top) Al 2024-T3–(Bottom) Al 5754-0, (Top) Al 5754-0–(Bottom) Al 2024-T3], overlap lengths (25, 40 mm), and impact energy (3, 11 J) on adhesive damage. The behavior of the joints determined by the numerical model under low-speed oblique impact was compared with experimental results. Considering the contact force-time, contact force-displacement, and adhesive damage, the numerical model was reasonably compatible with the experimental results. The damage initiation and propagation in the adhesive layer were determined by three-dimensional explicit finite-element analysis. In order to obtain suitability for the damage mechanism by observing the experimental bonding damage surfaces, the adhesive region was divided into three zones, the upper and lower adhesive interfaces and a middle adhesive layer between them. The different strength and plastic deformation ability of the adherends had a significant effect on the adhesive damage initiation and propagation. In the case of high strength and low deformation ability of the adherend material (Al 2024-T3) contacting with the impactor, a reduction of the adhesive damage occurred due to the deformation of the adherend material (bottom adherend) with low strength and high deformation capability. The oblique impact load and the different mechanical properties of the adherends greatly affected the adhesive damage initiation and propagation of single-lap joints.

This article presents the results of research on sandwich materials manufactured by liquid resin infusion and designed to resist in low-velocity/low-energy impact applications. The sandwich plates are made of composites skins [glass fiber reinforced plastic (GFRP)] on a foam core. A manufacturing method was designed to produce samples in a one-shot process. Four manufacturing parameters were selected and combined: resin’s temperature, preform’s temperature, hardener type, and presence of nanoscaled additives. Their influences on the behavior of the samples during impact and the resulting damages were investigated. For each manufactured plate, nine samples were impacted with a 10 J drop-weight tower. Impacted samples were inspected with two nondestructive testing methods, visual inspection and infrared thermography. Samples were cut afterward to confirm conclusions and observe in-depth damages. Two impact behaviors and three damage types have been identified among all tested samples. The impact properties of the samples can be directly linked to the processing conditions. To ensure uniform mechanical properties, plates should be manufactured with isothermal conditions (same temperature in the preform and in the resin). If the manufacturing temperature is high enough, there is no significant influence on the impact behavior of the sandwich samples using slow or standard hardener. The higher the infusion temperature is, the more brittle the resulting composite. With nanoadditives in isothermal conditions, the resin’s viscosity is much higher, leading to a longer infusion and nonuniform properties.

Abstract

The oscillation characteristics and morphological changes of the shock train in the inlet expansion section and the control of the shock train by surface arc plasma were studied in Mach 2 supersonic flow. A wedge installed at the exit of the supersonic inlet created a throttling ratio of 50% to generate a shock train in the expansion section. A high-speed schlieren system was employed to capture the flow structure of shock train. The fast Fourier transform (FFT) and snapshot proper orthogonal decomposition (SPOD) methods were employed to identify the oscillations’ spectral characteristics and for modal analysis of the shock train, respectively. The results show that the oscillation of $\lambda$ leading shock has the characteristics of multipeak frequencies with a range of $300–500\mathrm{Hz}$, and the Mach disk dominates the low-frequency oscillation characteristics of the $\lambda$ leading shock. The surface arc plasma actuation has a significant control effect on the shock train, realizing the conversion of the $\lambda$ leading shock to the oblique shock.

Practical Applications

As the first exploration of controlling the shock train in a supersonic inlet by surface arc plasma actuation, we found that the leading shock is transformed from $\lambda$ shock to oblique shock because of the excitation. During the whole control process, although the actuation changes the shape of the leading shock, the position of the leading shock hardly changes. The blast wave and the control gas bubble induced by the surface arc plasma actuation possibly can weaken the oscillation of the shock train and make it relatively stable in a certain position. In practice, there is a risk that the shock train will be pushed out of the inlet due to the back pressure. Surface arc plasma actuation may be able to balance the back pressure and suppress the excessive advance of the shock train. In the future, we will verify this and further expand the control ability of surface arc plasma actuation on the shock train.

This paper investigates an optimal orbit design method for single-satellite synthetic aperture radar tomography (TomoSAR) missions. Satellites require multibaseline observations for three-dimensional imaging. Thus, we need to weigh performance indicators such as global coverage, sampling rate, fuel consumption, and revisit accuracy. Considering these performance indicators, this paper proposes a multiobjective optimization algorithm based on multireference transfer orbit (M-RTO), which demonstrates superiority in fuel consumption. Fuel consumption is the primary optimization objective as it determines the lifetime of the satellite. First, we use Pareto optimization for the objectives of revisit time and fuel consumption. Then, we adopt an adaptive hybrid genetic algorithm (AHGA) for the objectives of revisit accuracy and fuel consumption. Numerical simulation verifies that compared with the single-reference transfer orbit method, the multireference transfer orbit method decreases fuel consumption by $\sim 37\%$, and the rest of the performance indicators meet the mission requirements.

In this paper, the potential of a novel active flow control strategy by means of a modulated pulse jet vortex generator to enhance high-lift performance is demonstrated on a two-dimensional supercritical National Aeronautics and Space Administration (NASA) SC(2)-0714 airfoil with a single slotted trailing-edge flap at a high deflection angle. Fast-switching solenoid valves and compressed air were used as actuators to excite the flow. The vortex generator slot pairs were incorporated into the shoulder of the trailing-edge flap, where the flow separation occurs due to the high flow deflection and severe adverse pressure gradient. In these experiments, in addition to the simple square-wave excitation signal, a burst-modulated excitation signal as a novel pulse jet sequence was implemented to produce the unsteady blowing. The burst-modulation signal was used for the first time for a fast-switching solenoid valve actuator. The experiments were performed at a freestream velocity of $25\mathrm{m}/\mathrm{s}$ with a corresponding Reynolds number of about ${1\times 10}^6$ for a range of angles of attack from 0° to 20° at flap deflection angles from 0° to 35°. The results indicated that the ejection from vortex generator slot pairs was able to prevent flow separation completely in most conditions. These measurements revealed that the burst-modulated excitation was accompanied by more aerodynamic improvements and less air consumption relative to the simple pulsed jet excitation. In the best flow control mode, the results showed about a 12.6% increase in the lift coefficient and a 19.8% decrease in the drag coefficient.

Fuel control is usually required to work with the acceleration and deceleration schedules to provide limit protection. However, limit protection will deteriorate controller performance. In this work, we investigate a model-based framework for gas turbine engine fuel control system. First, the gas turbine engine performance degradation due to the actuator saturation in fuel control system is described, and the thermodynamic component-level model and small deviation linear control model are obtained from the experimental data. Then, the problem of antiwindup in gas turbine engine control system is formed and the traditional static antiwindup compensator is introduced. Next, a dynamic antiwindup compensator based on Lyapunov stability is proposed to improve the control performance, and the design of the compensator is formulated and solved in linear matrix inequality framework. One of the notable features of the proposed approach is that the original controller does not need to redesign, and its previous control performance remains unchanged in set-point control. Compared with the static compensator in hardware-in-loop simulation, the proposed dynamic compensator can achieve better performance.