Hypersonic Vehicle Research Articles

Fast Trajectory Generation with a Deep Neural Network for Hypersonic Entry Flight

Optimal entry flight of hypersonic vehicles requires achieving specific mission objectives under complex nonlinear flight dynamics constraints. The challenge lies in rapid generation of optimal or near-optimal flight trajectories with significant changes in the initial flight conditions during entry. Deep Neural Networks (DNNs) have shown the capability to capture the inherent nonlinear mapping between states and optimal actions in complex control problems. This paper focused on comprehensive investigation and evaluation of a DNN-based method for three-dimensional hypersonic entry flight trajectory generation. The network is designed using cross-validation to ensure its performance, enabling it to learn the mapping between flight states and optimal actions. Since the time-consuming training process is conducted offline, the trained neural network can generate a single optimal control command in about 0.5 milliseconds on a PC, facilitating onboard applications. With the advantages in mapping capability and calculating speed of DNNs, this method can rapidly generate control action commands based on real-time flight state information from the DNN model. Simulation results demonstrate that the proposed method maintains a high level of accuracy even in scenarios where the initial flight conditions (including altitude, velocity, and flight path angle) deviate from their nominal values, and it has certain generalization ability.

Insight into jet-regeneration composite cooling technology employed in scramjet: Significance of relative positions of two jet holes

Due to the further increase in hypersonic vehicle speed, the scramjet faces supersonic combustion and aerodynamic heating, and the conventional single cooling method like regenerative cooling has been unable to meet the heat dissipation requirements of scramjet. The composite cooling system has become the hotspot of recent research. Jet cooling has a good cooling effect at high heat flux, so the jet-regeneration composite cooling method is innovatively proposed in this study. Compared with other composite cooling systems, the jet impingement can effectively weaken thermal boundary layer thickness. Initially, the total performance of the jet-regeneration composite cooling was experimentally verified via subcritical air. Furthermore, the numerical simulation of the jet-regeneration composite cooling was also carried out after the validation of turbulence models and mesh independence. Further examples, such as the jet impingement under the effect of the initial mainstream (so-called jet-mainstream) and regenerative cooling (so-called mainstream-only), are used to illustrate the advantages of this composite cooling (so-called jet-only). The heat transfer coefficient of jet-only is 2.6 times larger than that in the case of jet-mainstream. Compared with traditional regenerative cooling, even under the influence of the mainstream, the boundary layer thickness at the stagnation point of the jet impingement can be reduced by 40 times. This work is beneficial to the design of the jet-regeneration composite cooling system.

Investigation on the effect of the cooler design on the performance of onboard supercritical carbon dioxide power cycle for hypersonic vehicles

The scramjet cooling and power generation are the key demands for the hypersonic vehicle. To satisfy the cooling and electricity generation requirements of hypersonic vehicles, the onboard supercritical carbon dioxide (sCO2) power cycle is adopted in this paper. Moreover, the cooler design has a significant effect on the feasibility and overall performance of onboard sCO2 power cycle, but there is no research considering the effect of the cooler design. Accordingly, the effects of the cooler design on the overall performance of onboard sCO2 power cycles applied in hypersonic vehicles are comprehensively investigated based on the thermodynamic models. The results indicated that the optimum cooler designs are suggested to adopt a small channel diameter and a relatively large channel number for minimizing the cooler mass and fuel consumption for cooling sCO2 and maximizing the system thermal efficiency. Moreover, the cold channel diameter is designed to be smaller than the hot channel diameter. The cold channel number is required to be larger than the hot channel number. The total flow area of cold channel is smaller than that of hot channel. The geometric parameters of cooler hot channel could be designed based on the Re ranging from 15,000 to 34,000.

Three-dimensional trajectory tracking guidance against near-space maneuvering targets with multiple constraints under wind field

This paper presents a three-dimensional disturbance observer-based adaptive tracking guidance scheme for the trajectory tracking problem of a missile intercepting a hypersonic vehicle with the wind field, autopilot lag dynamics, and input saturation. Unlike most of the existing missile trajectory tracking guidance systems without velocity controllability and external wind field model, the wind field model is added to the dynamic model, and the velocity control channel is introduced into the three-dimensional trajectory tracking guidance problem to prevent impractical scenarios and increase tracking precision. The proposed tracking guidance methodology incorporates the sliding mode and adaptive control techniques, in which the sliding mode motion is finite time stable independently of the tracking guidance system's initial conditions. Also, the super twisting switch control law is added to cope with the chattering problem. In this context, external uncertainty disturbances and unmeasured states are lumped into lump disturbance and estimated using the backpropagation neural network extended state observer. To this end, numerical simulations demonstrate the tracking to reach zero between 3 s and 5 s against various uncertainties in engineering practical, and position tracking errors are within 0.15 m, superior to the existing tracking guidance methods.

Engineering Cf /ZrB2 -SiC-Y2 O3 for Thermal Structures of Hypersonic Vehicles with Excellent Long-Term Ultrahigh Temperature Ablation Resistance.

Ultrahigh temperature ceramic matrix composites (UHTCMCs) are critical for the development of high Mach reusable hypersonic vehicles. Although various materials are utilized as the thermal components of hypersonic vehicles, it is still challenging to meet the ultrahigh temperature ablation-resistant and reusability. Herein, the Y2 O3 reinforced Cf /ZrB2 -SiC composites are designed, which demonstrates near-zero damage under long-term ablation at temperatures up to 2500 °C for ten cycles. Notably, the linear ablation rate of the composites (0.33 µms-1 ) is over 24 times better than that of the conventional Cf /C-ZrC at 2500 °C (8.0 µms-1 ). Moreover, the long-term multi-cycle ablation mechanisms of the composites are investigated with the assistance of DFT calculations. Especially, the size effect and the content of the Zr-based crystals in the oxide layer fundamentally affect the stability of the oxide layer and the ablation properties. The ideal component and structure of the oxide layer for multi-cycle ablation condition are put forward, which can be obtained by controlling the Y2 O3 /ZrB2 mole ratio and establishing Y-Si-O - t-Zr0.9 Y0.1 O1.95 core-shell nano structure. This work proposes a new strategy for improving the long-term multi-cycle ablation resistance of UHTCMCs.

Advanced structural and multi‐functional sandwich composites with prismatic and foam cores: A review

AbstractAdvanced sandwich structures have emerged as new multifunctional structures with low density and good mechanical performance. Sandwich composites have high strength to weight and high stiffness to weight ratio. Good thermal and sound insulation can be provided using sandwich composite materials. Sandwich composites have high energy absorbing capacity. Multifunctional sandwich composites exhibit mechanical performance and other functional properties such as energy storage, electrical conductivity, etc. Further, the core can be used for routing wires, foam filling, fluid storage, embedding bars, etc. Thus, the multifunctionality can be introduced to the resuting composite materials. This article reviews current research on innovative sandwich structures with integrally woven corrugated core, honeycomb, foam, and 3D printed core architectures, emphasizing their multifunctionality. Aspects of sandwich structure with types of face and core structure design, material design, mechanical properties, and panel performance and damage, including multifunctional benefits, are reviewed. Examples of engineering and modern uses of sandwich structures are presented, covering hypersonic vehicles, civil and marine engineering, electronics, and biological fields. A list of areas for future study initiatives is also included. This review will serve as a baseline for future studies to do more research in the same direction.Highlights A detailed review of various types of core materials and sandwich structures is presented. Sandwich structures have high energy absorbing capacity. 3D woven sandwich structures, their manufacturing and failure mechanics is discussed. Modern applications of sandwich structures are detailed.

Study on the Variation of Gas Radiation Characteristics of Hypersonic Reentry Vehicles

For the nonequilibrium flowfield and high-temperature gas radiation spectral characteristics of the hypersonic reentry capsule, a spectral prediction method based on quasi-steady-state assumption and line-by-line method is introduced. Meanwhile, the characteristics of the spectrum are studied to investigate the influence of viewing angles and trajectory points during reentry based on this method. We use Fire II flight test data to verify the accuracy of the gas radiation model and update the prediction values of the cumulative radiation intensity in the wavelength range of 2.2–4.1 eV by previous methods. The results show that the radiation signal is most significant at the stagnation line and gradually decreases with the deviation of the line of sight from the stagnation line. The cumulative radiation intensity of the various trajectory points exhibits a profile that increases and then decreases during reentry; it rises to its peak at 50 km. The emission spectrum of gas radiation is mainly distributed in the ultraviolet and near-infrared bands. The transition processes of atoms N and O contribute more than 90% of the total radiation intensity, and the contribution of the first negative series in the molecular spectrum is relatively considerable compared to other molecular components.

Kinetic insight into composition effect on the laminar flame speeds of cracked endothermic hydrocarbon fuel for hypersonic vehicles

Hydrocarbon fuels are promising energy sources and coolants for hypersonic vehicles. A clear understanding on the oxidation mechanism discrepancies of different cracked endothermic hydrocarbon fuels is essential for the performance and thermal management of hypersonic vehicles. Kinetic analyses on the pathway flux, sensitivity, and producing rate were performed to reveal the intrinsic relationships between the composition variation and laminar flame speeds of different pyrolysis products. A skeletal mechanism containing 68 species and 326 reactions was developed and validated by the targeted properties of the pyrolysis products. Analyses showed the flame speed discrepancies were resulted from the kinetic effect of the composition variations. The main oxidation pathways and consumption rates of the key intermediates were hardly changed with composition variation in the pyrolysis products. Sensitivity analyses found the flame speeds of pyrolysis products were mainly affected by the H/O/OH addition reactions of C0–C2 species. Their sensitivity coefficients were independent of the composition variations. Analyses on the rate of product (ROP) indicated the composition variation has a significant effect on the ROPs of H/O/OH radicals. Pyrolysis products including compositions of higher H/C ratios can produce higher contents of H, O, and OH radicals for the flame, resulting in higher laminar flame speeds.

Multi-physical analysis of ablation for C/C composites based on peridynamics

C/C composite material is one of the most widely used thermal protection materials for hypersonic vehicles. As coupled with fluid dynamics, chemical reaction, heat transfer and ablation recession, its numerical simulation is challenging and complicated. In this study, a multi-physical analysis approach for the stripping process during ablation based on peridynamics is proposed. Aerodynamic parameters and heat flux distribution are determined by empirical formulas. The energy balance on the ablative wall has been taken into account for the thermal boundary conditions and the temperature field is obtained by using bond-based peridynamics. Then, the temperature-dependent dimensionless mass flux and surface recession rate are evaluated by solving the equations involving mass conservation of surface elements and chemical equilibrium of reactions. Meanwhile, considering the breaking of bonds and the deletion of material points in this model, the phenomenon of ablation and stripping process of material on the surface can be simulated. A C/C one-dimensional model is built to verify the effectiveness of the methodology, and the peridynamic results agree with the experimental observation from literatures well. Finally, after combining fluid dynamics, chemical reaction, heat transfer and ablation recession, the exterior shape and temperature field at a nose tip of a hypersonic vehicle are predicted.

Epistemic modeling uncertainty of rapid neural network ensembles for adaptive learning

Emulator embedded neural networks, which are closely related to physics informed neural networks, leverage multi-fidelity data sources for efficient design exploration of aerospace engineering systems. Multiple realizations of the neural network model are trained with different random initializations. The ensemble of model realizations is used to assess epistemic modeling uncertainty caused by a lack of training samples. This uncertainty estimation is crucial information for successful goal-oriented adaptive learning in an aerospace system design exploration. However, the costs of training the ensemble models often become prohibitive and pose a computational challenge, especially when the models are not trained in parallel during adaptive learning. In this work, a new type of emulator embedded neural network is presented using the rapid neural network paradigm. Unlike the conventional neural network training that optimizes the weights and biases of all the network layers by using gradient-based backpropagation, rapid neural network training adjusts only the last layer connection weights by applying a linear regression technique. It is found that the proposed emulator embedded neural network trains near-instantaneously, typically without loss of prediction accuracy. The proposed method is demonstrated on multiple analytical examples, as well as an aerospace flight parameter study of a generic hypersonic vehicle.

Prescribed-time control for hypersonic morphing vehicles with state error constraints and uncertainties

This paper focuses on the attitude control problem of hypersonic morphing vehicles (HMVs) with output state constraints and uncertainties in morphing phase. The main contribution of this work is not only realizing arbitrarily predefined settling time based on accelerated tracking rate but also ensuring smooth control performance under morphing effects and uncertainties. Firstly the control-oriented model is established based on the dynamic model of HMVs. Then, a prescribed-time disturbance observer (PTDO) is developed to enhance the robustness of flight control system based on radial basis function neural networks (RBFNN), allowing the lumped disturbances to be estimated within appointed time. Subsequently, based on tangent-type barrier Lyapunov function (TBLF) and prescribed-time convergence technique, the controller is designed via backstepping method, and the tracking errors of output states converge to the near origin within arbitrarily prescribed time without violating the preassigned constraints during tracking process. Finally, the closed-loop stability is ensured via Lyapunov synthesis, and numerical test results are presented to demonstrate the effectiveness of the proposed control scheme. Simulation results show that superior performance is obtained in terms of both transient process and stabilization.

Investigation on flow and heat transfer of fluid in self-driven circulation system for transpiration cooling

Transpiration cooling has attracted extensive attention from industry as an efficient thermal protection strategy to cope with the extreme thermal environment during hypersonic vehicle flight. Unfortunately, the investigation on transpiration cooling in combination with internal coolant piping layout is inadequate. Here, we propose a self-driven natural circulation system as the internal coolant channel in the lower layer of the transpiration cooling structure, aiming to achieve comprehensive thermal management. Meanwhile, a time-resolved Quantitative Light Sheet technique is applied in experimental research on the natural circulation system. Through investigating the flow, heat transfer and phase transition characteristics of the fluid in the system, it is concluded that this system utilizes the heat flux difference loaded on the pipe wall to drive the coolant to circulate in the loop, and the maximum wall heat flux reaches about 15.4 kW/m2, realizing internal self-adaptive cooling. Additionally, this proposed system ensures that the phase transition occurs in the lower pipes of the transpiration structure to avoid heat transfer deterioration. Besides, the system releases 57,600 cm3 steam within 100 s under the 500 W/m2 heat flux difference of pipes acting as coolant for transpiration cooling. Thus, this work provides an innovative reference for combined application of transpiration cooling and self-driven natural circulation system.

Formation of N(2D) from Hyperthermal Collisions between O(3P) and NO(X2Π).

Hyperthermal collisions between O(3P) and NO(X2Π) could lead to the formation of the first electronically excited atomic nitrogen (N(2D)), which plays a key role in plasma formation in shock-heated air. This process is facilitated mainly by four doublet states, and to a much lesser extent by two quartet states. In this work, we report quasi-classical trajectory studies of this reactive process using the four analytical adiabatic potential energy surfaces for the doublet states developed previously from fitting high-level ab initio data. The reactions were found to be strongly enhanced by vibrational excitation of the NO reactant, consistent with the existence of potential energy barriers in the exit channel. Despite the large endothermicity of the reaction, the rate coefficient is significant at high temperatures, suggesting a possible role of this reaction in the hyperthermal kinetics in the shock layer of a hypersonic (re)entry vehicle.

Heat transfer performance investigation of rotating U-channel supercritical pressure hydrocarbon fuel with intermediate connection section

To meet the challenge of the high temperatures faced by hypersonic vehicle electricity provision turbine blades, the blades are cooled with hydrocarbon fuel. For reducing the friction loss and improving the thermal performance, this paper designs and investigates the fuel flow mechanism and heat transfer law in the rotating channel with and without intermediate connection section. The results show that the channel with intermediate connection sections can reduce the friction coefficient of hydrocarbon fuel under rotating conditions and enhance the thermal performance. The connection section width H = 2D channel exhibits the best thermal performance and the lowest coefficient of friction. Compared to the channel without intermediate connection section, the thermal performance of the channel with connection section width H = 2 D is maximally enhanced by 3.71 times and the friction coefficient is maximally reduced by 98.9%. Compared to stationary, the thermal performance of the channel with a width of connection section H = 2 D is maximally enhanced by 10.78 times in rotating. Connecting sections will gradually replace 180° top turning sections. When the inlet temperature increases, the thermal performance of the channel can be improved by decreasing the width of the intermediate connecting section.

Key features and highly effective prediction of complete startup from frozen state for high-temperature heat pipe in heat pipe reactor

High-temperature heat pipe is an efficient phase change heat transfer device, widely applied in the space nuclear reactors, the China Fusion Engineering Test Reactor, solar collectors, and the thermal protection of hypersonic vehicles. In order to understand the startup characteristics of the heat pipe and to predict its transient behavior with high accuracy, this paper first experimentally investigated the startup performance of a sodium heat pipe from the frozen state under different heating powers from 534 W to 1897 W. Then, a new compressible flow model for startup from the frozen state was developed and verified, solved the independence problems of mesh number and time-step used in the numerical treatments of most traditional heat pipe codes. Finally, based on the assessed model and experimental data, the startup procedure and the influences of heating power on the working temperature, kick-in time, and temperature difference were analyzed respectively. The comparisons indicated that the new model is extremely informative and effective, and the results provided knowledge for understanding the safe and optimum working regime of a high-temperature heat pipe using in heat pipe reactor.

Fault-tolerant learning control of air-breathing hypersonic vehicles with uncertain parameters and actuator faults

This paper investigates fault-tolerant learning control for air-breathing hypersonic vehicles (AHVs) subject to parametric uncertainties, external disturbances, and actuator faults. By treating the flexible dynamics as equivalent disturbance, the AHV model can be decomposed into velocity subsystem and altitude subsystem. An intelligent fault diagnosis approach is deployed to estimate the actuator fault information for each subsystem sequentially. Furthermore, combined with a fixed-time neural disturbance observer, composite learning control is deployed to construct control commands using the historical stack to improve the learning accuracy, while compensating for lumped disturbances, including fault diagnosis errors and external disturbances. The designed controller addresses the fault-tolerant tracking problem by combining offline and online learning strategies, which is a significant advantage over other existing AHV controllers. Simulation results validate the effectiveness of the fault-tolerant learning control.

Adaptive backstepping fault-tolerant control for hypersonic aircraft with unknown control direction under actuator and sensor faults

Abstract In this paper, an adaptive backstepping controller of hypersonic flight vehicle (HFV) system is investigated in the presence of unknown actuator and sensor faults, unknown control direction and varying external disturbance, which expands traditional fault-tolerant control (FTC) approaches in HFV field. The control-oriented model is established with reasonable and comprehensive analysis of various fault types. Compared with the previous FTC research on HFV system, the time-varying and fixed fault types are simultaneously designed for actuator and sensors, and the control direction is unknown, which can more accurately simulate the real fault situations in the hypersonic flight environment. To avoid singularity problems caused by the unknown control direction, the Nussbaum gain function technique is adopted in the control algorithm, which is also capable of overcoming the influence of unknown time-varying fault parameters. The boundness and stability of system under the designed control scheme are theoretically verified. Finally, numerical simulation results demonstrate the effectiveness and superiority of the proposed control strategy.

Study on Ground Experimental Method of Stagnation Point Large Heat Flux of Typical Sharp Wedge Leading Edge Structure

In this paper, aimed at the problem of large temperature gradient thermal testing with the typical sharp wedge leading edge structure of a hypersonic vehicle, a subsonic high-temperature combustion gas heating (SHCH) test device is used to conduct a series of experiments on the heat flux simulation ability of subsonic high-temperature combustion gas in the stagnation point region. Firstly, for a hypersonic vehicle with a flying height of 24 km and Mach number range of 4~6.5, the stagnation point heat flux in the head area is obtained by numerical calculation of a typical leading edge structure, which is used as the experimental target of the thermal structure test. Secondly, an experimental specimen with a Gardon heat flux meter is designed with the same shape and size as the specimen in the numerical simulations to prepare for the subsequent SHCH test. Thirdly, a method to determine the combustion gas temperature based on a Kriging surrogate model is proposed. CFD numerical simulation is conducted using the SHCH test model, and the numerical calculation results are used as the training dataset. The Kriging surrogate model is used to establish an approximate fitting relationship between the stagnation point heat flux and experimental parameters under SHCH conditions. The corresponding combustion gas temperature values are found, respectively, with the hypersonic aerodynamic heat flux at Mach 5.0~5.4 as the target value. Finally, stagnation point heat flux testing of low-speed and high-temperature combustion gas is performed at different combustion gas temperatures. The experimental and target values obtained from hypersonic aerodynamic thermal simulations are compared and analyzed to verify the heating capacity of SHCH and the feasibility of hypersonic aerothermal simulation testing.

Anti-disturbance control for HVs system subject to nonlinear actuator characteristics with extended state observer

This paper proposes a radial basis function neural network and the actuator fault extended state observer based fast non-terminal sliding mode fault-tolerant control scheme for hypersonic vehicles (HVs) system. The proposed scheme can cope with actuator faults, actuator saturation, parameter uncertainties, and external disturbances for HVs systems, without relying on redundancy as some passive FTC methods do. Moreover, an anti-windup compensator is designed to mitigate the input saturation effects. Furthermore, the finite-time stability of the attitude angle of the HVs system is proved by Lyapunov's theorem. Numerical simulations validate the effectiveness of the proposed scheme.

Experimental study on the mechanism of water on heat sink variation in catalytic partial steam reforming of supercritical n-decane

Regenerative cooling is an effective method for heat management of hypersonic vehicles and faces a problem of insufficient cooling capacity under higher flight Mach number. Water-assisted hydrocarbon fuels thermal conversion can effectively increase heat absorption and inhibit carbon deposition. The mechanism of water on the variation of heat sink is unclear. In this study, experimental study was conducted to investigate the effect of different water contents, pressure and mass flow rates on the variation of heat sink and the distribution of gaseous products in a continuous experimental system. The results show that catalytic partial steam reforming reaction consists of catalytic steam reforming and catalytic thermal cracking in the low temperature stage (T＜490 ℃), and non-catalytic thermal cracking is activated and gradually dominate in the high temperature stage (T＞490 ℃). The contribution of water to total heat sink is mainly caused by physical heat sink. Increasing mass flow rate mainly suppress the cracking reaction in the high temperature section by reducing reaction residence time. The flow rate has little effect on the chemical reaction equilibrium. Higher pressure has little effect on heat sink, but accelerates carbon deposition by promoting the formation of olefin products.