Journal of Aerospace Engineering

A numerical simulation is performed to investigate a passive jet flow control method for suppressing the alternating vortex shedding from the circular cylinder. A hollow pipe is tightly set on the circular cylinder, and two arrangement cases for the holes are employed: one is a five-hole case, which means that five suction holes are set near the front stagnation point and five jet holes set near the rear stagnation point of the cylinder. The other is the full-hole case, which means the holes are equidistantly arranged on the hollow pipe. The incoming flow enters the suction holes and jets into the near wake from the outlet holes. Consequently, the wake vortex shedding alternately is manipulated or destroyed. The numerical simulations of baseline cases (without control) are first conducted to verify the reliability of the numerical model. Next, the two controlled cases (five hole-case and full-hole case) are investigated at the Reynolds number $\mathsf{R}={10}^3-{10}^5$. It is found that a remarkable mitigation for the aerodynamic forces of the cylinder is revealed at the high Reynolds number: the in-line drag coefficient can be reduced by approximately 40.00%. At the same time, the cross-flow lift fluctuation has been completely suppressed with a control effectiveness of more than 98.00%. The swirling strength distributions and corresponding streamline results around the circular cylinder are then described, which are employed to present the essential physics regarding why the unsteady vortex shedding is suppressed by the passive control method. Finally, the stability of the flow field is discussed based on the linear stability theory. The absolute instability region near the cylinder shrinks substantially at the high Reynolds number, even changing into a convective instability region completely for the five-hole cases.

This paper addresses the cooperative search problem for a team of unmanned aerial vehicles (UAVs) with limited field-of-view (FOV) and available overload constraints. First, the models of environment, UAV, image sensor, and communication are established. Second, a modified distributed information fusion strategy based on the Bayesian rule is proposed, which can make all the individual probability maps converge to the same one and reflect the true existence or nonexistence of targets within each cell. Third, a distributed gradient-based optimization method for path planning involved in the cooperative search is proposed and the available overload constraint of the UAV can be taken into account. Fourth, the aforementioned distributed gradient-based optimization method is improved by involving collision avoidance, establishing reasonable safety distance constraints, and using the Lagrange multiplier. Finally, the correctness and effectiveness of the proposed method are validated and demonstrated via simulations.

An equal polygon opposing jet can withstand huge wave drag and serious aerodynamic heating in hypersonic flow conditions. The opposing jet is able to change the flow field structure, and then it improves the aerodynamic characteristic of the hypersonic vehicle. In order to get more information about the flow field characteristics of the opposing jet, the schemes with equal polygons for the opposing jet were designed and their properties with different polygons have been investigated numerically in the paper. Also, the numerical method has been validated against the available experimental data in the open literature. The obtained results show that the drag-reduction performance is best when the number of jet angles ($N$) is 7, and its value reaches 26.4%. At the same time, its wall maximum heat flux is the smallest and the performance for heat protection is the best. Moreover, the maximum heat flux can be decreased by 60.6%. $N$ has a slight influence on the position of the shock wave. When $N$ is big enough, the difference for the flow field between the novel scheme and circle jet is very small because of the influence of the three-dimensional flow. But its practicability is not good. When $N$ is not less than 4, the maximum heat flux sits in the datum line of the jet angle. The contour for wall heat flux owns the characteristics of the polygon. The flow control can work when $N$ is an odd number.

In this work, four key design parameters of cycloidal rotors, namely the airfoil section, number of blades, chord-to-radius ratio, and pitching axis location, are addressed. The four parameters, which have a strong effect on rotor aerodynamic efficiency, are analyzed with an analytical model and a numerical approach. The numerical method, which is based on a finite-volume discretization of two-dimensional unsteady Reynolds averaged Navier-Stokes equations on a multiple sliding mesh, is proposed and validated against experimental data. A parametric analysis is then carried out considering a large-scale cyclogyro, suitable for payloads above 100 kg, in hovering conditions. Results demonstrate that the airfoil thickness significantly affects the rotor performance; such a result is partly in contrast with previous findings for small-scale and microscale configurations. Moreover, it will be shown that increasing the number of blades could result in a decrease of the rotor efficiency. The effect of chord-to-radius will demonstrate that values of around 0.5 result in higher efficiency. Finally it is found out that for these large systems, in contrast with microscale cyclogyros, the generated thrust increases as the pitching axis is located away from the leading edge, up to 35% of chord length. Furthermore, the shortcomings of using simplified analytical tools in the prediction of thrust and power in nonideal flow conditions are discussed.

The filtered Rayleigh scattering technique was implemented to discern the mechanisms associated with trajectory and mixing characteristics of buoyant jets in the presence of a coflow. A continuous wave laser in conjunction with a high-speed camera and a molecular filter constituted the equipment needed to obtain near-field concentration measurements of a carbon dioxide jet within a coflow of air. The arrangement enabled carbon dioxide concentration measurements with and without the coflow at a sampling rate of 400 Hz. The time-averaged results demonstrate the significance that adding the coflow has on increasing the mixing rate, thus reducing the impact of the buoyant jet by flattening the jet trajectory. The effects of various flow parameters such as the jet velocity, the jet to coflow velocity ratio, the relative velocity between the jet and the coflow, and the Froude number on the jet trajectory are studied. The downward trajectory of the carbon dioxide jet, absent a coflow, was well correlated with the Froude number. However, the addition of the coflow led to a substantial impact on the jet trajectory, reducing its buoyant effects due to a combination of increased momentum and, likely, the mixing rate. Further increases in the coflow, including the relative magnitude of the coflow, had a lesser impact. Mixing characteristics and time-dependent jet motion were captured.

X-ray pulsar navigation techniques can provide the information of position and velocity for spacecraft and have proven to be an extremely promising autonomous navigation solution. Currently, one of the main problems of pulsar navigation is that the update rate of the measurement data is low. In this paper, a multirate observation pulsar navigation model is proposed to improve the update rate of measurement data. To solve the uncertainty of the measured angles in the multirate observation model of pulsar navigation, a robust extended Kalman filter (REKF) is also proposed. In order to verify the effectiveness of the model and filtering algorithm, the root-mean square (RMS) errors of the REKF for multirate observation model is compared with the extended Kalman filter (EKF) for a multirate observation model and REKF for a synchronous observation model. The simulations results show that the proposed multirate observation model and REKF are valid to improve navigation accuracy.

The variable-geometry turbine is often used to improve the gas turbine part-load performances; however, there are performance penalties associated with the vane-end part clearance that is required for the smooth movement of variable-geometry vanes. To determine the effects of tip cavity on tip clearance flows in a variable-geometry vane, experimental investigations with a variable-geometry turbine linear cascade have been conducted. The tip-cavity effects on the overtip-leakage flow and losses, and the effects of turning angle on the total pressure losses and the yaw angle are considered. The measurement results show that the variation of vane-turning angles completely changes the vane-loading distribution. As the vane-turning angle varies from design to closed, the vane loading increases and tends to be more aft loaded, thus increasing the tip-leakage loss, and vice versa. At all turning angles, the tip-leakage vortex is weakened by the tip cavity, and the cavity tip plays a significant role in reducing aerodynamic losses. The results can provide guidelines for the vane-end clearance control of variable-geometry turbines.

To improve the computational efficiency of the reliability-based design optimization (RBDO) of a complex structure with nonlinear and implicit limit-state function, the single-loop-single-vector (SLSV)-limit-state factor (LSF) (SLSV-LSF) method was developed by fully considering the advantages of the SLSV approach and the LSF method to transform uncertain constraints into deterministic constraints. The mathematical models of SLSV and LSF were established and the basic RBDO process of the SLSV-LSF method is presented. The shape optimization of an aeroengine turbine disk was completed based on the proposed method. From the reliability sensitivity analysis of the turbine disk, it is revealed that an uncertain constraint of average circumferential stress can be transformed into a deterministic constraint and material density can be regarded as a deterministic variable. Through the min-mass shape design of the turbine disk based on different approaches, it is demonstrated that the developed method maintains high computational speed and efficiency while keeping maintaining computational accuracy, which validates the feasibility and validity of the SLSV-LSF method in the RBDO of aeroengine typical components.

A design methodology is presented that supports the design of future aerospace rocket-powered vehicles. In particular, it provides the capabilities to rapidly evaluate the performance, weight, size, and lifecycle costs of all chemical rocket engines at a conceptual level. By leveraging cycle-based approaches and surrogate modeling techniques, the performance of all chemical rocket engines can be evaluated with an accuracy of 3%, whereas it divides the execution time by a factor of ${10}^5$ compared to current physics-based models. New mass-estimating relationships are developed for estimating the weight and the size of solid engines with an improved accuracy compared to existing models. Physics-based models built around the key design drivers are used for the weight and size estimation of liquid and hybrid engines. Although existing cost-estimating relationships are used to evaluate the lifecycle costs of solid and liquid engines, a more physics-based model is developed for hybrid engines. Although it supports complex multiobjective optimizations and rapid trade-off analyses, this environment is also the first of its sort able to estimate the lifecycle costs of hybrid rocket engines.

Based on the characteristics of manually controlled rendezvous and docking, this paper proposes a novel discrete inverse-simulation method for investigating handling qualities. The proposed method was verified by teleoperation console experiments. The steady-state error and stability were analyzed using $Z$-domain criteria and verified by theoretical simulation. Furthermore, to reduce the high-frequency oscillations caused by the observed errors, the inverse-simulation method was modified by combining it with adaptive predicted-threshold filtering. The simulation results indicate that the modified inverse strategy can be used to dampen the oscillations and better reproduce maneuvers.

This investigation demonstrates the deposition of copper and titanium nitride on a polymeric composite using physical vapor deposition (PVD) to increase the thermoelectrical properties of the composite. The physicothermal characteristics of the polymeric composite and conductive polymeric composite were characterized using field electron scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). Electrical conductivity of the basic and conductive composites was determined using the four-probe method of resistivity measurement. It was observed that thermal properties and electrical conductivity of the composite increased significantly due to the coper and titanium nitride deposition. The basic and conductive polymeric composite were subjected to high current and temperature to simulate the effect of a lightning strike. It was observed that there is a severe damage to the basic polymeric composite compared to the conductive polymeric composite, resulting in significant deterioration of mechanical properties.

In this work, a control moment gyroscope (CMG) supported by active magnetic bearing (AMB) is considered with a gimbal angular movement. Gimbal angular movement in a CMG imposes extra load on magnetic bearings. A complete model of the CMG system with flywheel, AMBs, and gimbal dynamics is derived for control design. Lyapunov based composite adaptive output feedback control is proposed for fast uncertainty compensation in the CMG system, and some simulation results are presented. For a gimbal angular velocity input, a flywheel rotor magnetic bearing system is simulated at constant rotational speed of the flywheel rotor.

In this work, the static aeroelastic behavior of flexible aircraft with a high aspect ratio wing undergoing large static deformations has been investigated analytically and numerically. Toward this end, a nonlinear structural model based on a simple one-dimensional nonlinear beam theory is used. An efficient evaluation of static deformation of the entire high-altitude long-endurance (HALE) airplane is developed by adopting the single beam model to the wing, the fuselage, the vertical fin, and the tail, and merging all the substructures together. This model can deal with arbitrarily large displacements and rotations of the whole airplane by use of Euler angles and can account for various structural couplings. Static results due to simple external loads are shown for demonstration. Then, the paper discusses coupling the beam model with several aerodynamic models to investigate the static aeroelastic performance of the high aspect ratio wing. Comparisons of the aerodynamic tools are made in terms of numerical efficiency, simplicity, and further applications. Among these aerodynamic models, the unsteady vortex lattice method (UVLM) is given special attention since it offers convenient and accurate prospects in analyzing the dynamic behavior of the HALE aircraft.

An integrated finite-time disturbance observer (FDO) and attitude controller is designed for a reusable launch vehicle (RLV) in this paper. In accordance with the multiple-timescale features, RLV attitude dynamics are divided into an outer-loop subsystem and an inner-loop subsystem. Based on the recently developed sliding mode control (SMC), a novel multivariable supertwisting sliding mode controller driven by a FDO is designed to achieve a fast and accurate reentry attitude tracking. This integrated design can generate a continuous control law which has excellent robustness to uncertainty and disturbances with known bounds while achieving an arbitrarily fast convergence. The finite-time stability of the overall system is proved by using the Lyapunov function technique and the multiple-timescale separation principle. In addition, an optimal control allocation for allocating torque commands into aerodynamic surface deflection commands with constraints is also proposed. Finally, the effectiveness and the robustness of the integrated control scheme are verified by the simulation results of a six-degree-of-freedom (6-DOF) RLV.

This article explores the steady mixed convection stagnation-point flow of Powell-Eyring fluid in the presence of thermal radiation, heat generation/absorption, and chemical reaction. Suitable transformations are considered to reduce nonlinear boundary layer partial differential equations into ordinary differential equations. Convergent series solutions of the resulting dimensionless problems are obtained. The effects of emerging physical parameters on the velocity, temperature, and concentration profiles are examined. Numerical values of skin-friction coefficient and local Nusselt and Sherwood numbers are tabulated and analyzed for different values of emerging parameters. A comparative analysis with existing solutions in a limiting sense is made.

The work presented in this paper addresses the longitudinal parameter estimation of an unmanned configuration using wind tunnel testing and flight data. For this purpose, an unmanned aerial vehicle has been designed with a cropped delta planform and rectangular cross-section. Exhaustive full-scale wind tunnel tests were carried out on the designed unmanned flight vehicle to capture the linear and nonlinear variation of aerodynamic force and moment coefficients. The measured wind tunnel test data, in the form of signals, have been processed to forces and moments about the desired reference point of the designed unmanned platform. A comprehensive discussion on the obtained results from wind tunnel testing has been presented. In order to enhance the confidence in the generated aerodynamic database from wind tunnel testing and also to estimate the dynamic derivatives, two sets of real flight data pertaining to longitudinal dynamics (acquired during the flight tests) have been used. The parameter estimation in the linear domain has been carried out using conventional maximum likelihood and least-square methods. The estimated longitudinal parameters from the flight data were used to corroborate the aerodynamic coefficients derived from the wind tunnel measurements.

A numerical-simulation tool is developed that is well suited for modeling the unsteady and nonlinear aerodynamics of flying insects and small birds as well as biologically inspired flapping-wing micro air vehicles (MAVs). The tool consists of a combination of (1) an aerodynamic model that is an extension of the widely used three-dimensional (3D) general unsteady vortex-lattice model, and (2) a general kinematic model that is capable of describing multiple deformation patterns of lifting surfaces, such as spanwise twisting, in-plane and out-of-plane bending, and any combination of these. Moreover, the present tool offers an attractive compromise between computational cost and fidelity and is ideally suited to be combined with computational structural dynamics to perform aeroelastic analyses. The present tool was successfully validated by comparing some of the present results with those obtained from existing numerical models based on both Euler equations and vortex-lattice codes and with some experimental data. Using the numerical framework developed and for the deformation mechanisms analyzed here, two distinctly different effects were found: the wing span’s twisting and in-plane bending affect the lift in specific zones of the stroke cycle (called “local behavior”); and the wing span’s out-of-plane bending affects the lift throughout the stroke cycle (called “global behavior”). In addition, the results found show that the wing’s flexibility certainly affects the lift production, at least for some flights at small scales. These findings definitely suggest the strong likelihood that the unsteady vortex-lattice method combined with a general kinematic model can be a very accurate and efficient tool for future aeroelastic studies.

A prognostic model capable of predicting temporal damage evolution is essential to prevent catastrophic failure of structures. Data driven techniques, such as neural networks and support vector machines, are widely used for prediction of damage in a variety of aerospace and civil applications. Most of the available techniques cannot be applied for real-time prediction because they assume the measured value to be the true value, which is often not true. They also require training data from a similar set of experiments based on which predictions are made, which may not always be available. In this paper, the authors propose a novel integrated approach that intelligently combines particle filter updating with a fully probabilistic Gaussian process model to predict complex physical phenomena (e.g., temporal local pier scour) considering both measurement and prediction uncertainties. In this example, the measurement model is obtained using radio frequency identification (RFID) sensors and the state space model is the Gaussian process-based prognosis model. The performance of the algorithm was tested using corrupt training data. Different scenarios are presented with application to predicting local scour near bridge piers, which is a highly stochastic phenomenon with training data mostly unavailable. The algorithm is used to make predictions using corrupt training data. The results indicate that the proposed approach predicts the scour depth accurately under varying field conditions.

An investigation of the unsteady hydromagnetic natural convection flow of a viscous, incompressible, electrically conducting, and heat-absorbing fluid past an infinite vertical plate through a fluid-saturated porous medium with a time-dependent free stream in a rotating system with Hall effects is carried out. An exact solution of the governing equations is obtained using the Laplace transform technique. Two cases of interest are discussed, viz, (1) the impulsive movement of the free stream and (2) the accelerated movement of the free stream. Expressions for the shear stresses at the plate as a result of the primary and secondary flows and the rate of heat transfer at the plate are derived. Asymptotic behavior of the solution is analyzed for both small and large values of time $t$ to highlight the transient approach to the steady-state flow and to gain some physical insight into the flow pattern. A reverse flow exists in the secondary flow direction because of the presence of the thermal buoyancy force and the time-dependent movement of the free stream, which has not yet been reported in the literature.

In this study, an analysis was performed for numerical Soret-Dufour heat and mass transfer of a steady laminar boundary-layer flow with Ohmic dissipation, electromagnetic hydrodynamic (EMHD) porosity, and buoyancy multimedia physical features about extrusion processing for a stretching sheet. There are many applications in the manufacturing of foods and paper and other similar activities, such as extrusion processing, cooling systems or heat exchangers, which might greatly reduce the required pumping power. A modified numerical solution of the flow velocity distributions, temperature profiles, and the wall unknown values of ${\theta }^{\prime }(0)$ and ${\varphi }^{\prime }(0)$ for calculating the heat and mass transfer of the similar boundary-layer flow are carried out as functions of the viscoelastic parameter $E$, the Prandtl number $\mathsf{Pr}$, and the buoyancy parameters Gr and Gc. Values of $E$, $\mathsf{Pr}$, E1, Gr, and Gc parameters are important factors in this study. Although a greater heat transfer effect will be produced with a larger value of these parameters, the magnetic parameter $M$, porosity parameter DL, Dufour number Df, Eckert number Ec, and Soret number Sr may reduce the heat transfer effect. In this study, for mass transfer, the value of Schmidt number Sc is an important factor. Although the larger value of Sc will produce a greater mass transfer efficiency, the Soret number Sr has a negative effect on the mass transfer process.

Hypersonic glide vehicles will be limited by many constraints during their flight course. The flight corridor is defined as the intersection of these constraints and plays an important role in trajectory planning and optimization. Mathematical models of the flight corridor are established in a drag acceleration-velocity (D-V) profile and a height-velocity (H-V) profile. Further analysis of the flight corridor of hypersonic glide vehicles is carried out from the perspectives of influence factors and uncertainties. A credible and simple existence criterion is proposed to avoid iteration. This paper is aimed at improving the understanding of flight corridors of hypersonic glide vehicles and providing valuable information for missions, such as trajectory planning and optimization.