Air-breathing Hypersonic Vehicle Research Articles

Refined mode classification and performance analysis method of dual-mode scramjet vehicles for flight trajectory optimization

Hypersonic air-breathing vehicles, utilizing ramjet and scramjet propulsion systems, are emerging as a promising option for future hypersonic transportation due to high specific impulse. The performance of hypersonic aircraft is significantly influenced by their flight trajectory, as combustion efficiency and aerodynamic forces vary markedly with altitude. Although numerous studies have focused on optimizing these trajectories, they have not adequately considered the potential for operational failures in the propulsion system, such as unstart and blowout. This study introduces a trajectory optimization approach for hypersonic aircraft that proactively addresses and mitigates these operational failures. This is achieved by establishing an operational classification process for a dual-mode scramjet engine and proposing a failure mode avoidance strategy using a Gaussian process classifier. Optimized ascent trajectories are achieved through the development of a two-stage robust sequential convex programming approach. The results of trajectory optimization indicate that the failure mode avoidance strategy proposed is crucial in obtaining minimal time trajectories, and that the optimal trajectories include drop motion in the initial stage flight in order to increase combustion efficiency.

An experimental study on the combustion characteristics of the cavity-stabilized supersonic premixed flame

With the overwhelming trend of fast and economic aviation, it is becoming increasingly difficult for fuel to burn stably and efficiently in a constrained space and time period in the combustor of a hypersonic air-breathing vehicle. Conventional supersonic diffusion flame runs the risk of blowing out in the incoming flow at such high velocity. Upstream fuel injection of the flame holder is gaining popularity due to its prominent advantage in improving mixing efficiency, and this fuel injection method contributes to the organization of supersonic premixed combustion. In order to study the combustion characteristics of the supersonic premixed flame, corresponding experiments are carried out on a direct-connected scramjet platform with the inflow total temperature of 1700 K and the inflow Mach Number of 2.0. Gaseous ethylene with an equivalence ratio of 0.15 was injected transversely 670 mm upstream of a cavity. Optical measurements including laser-induced fluorescence on the hydroxyl radical (OH-LIF), CH*chemiluminescence photography, and high-speed photography were performed to investigate the steady-state and transient combustion characteristics of the cavity-stabilized supersonic premixed flame. From steady-state OH-LIF and CH* results, the flame could be divided into reactant zone, preheating zone, intense reacting zone, and product zone. It could be inferred that the preheating zone induced by the hot product in the cavity acts as a radical source and heat source for combustion stabilization in the cavity. In addition, the transient flame morphology analysis was carried out from the high-speed photography results. The flame base position and flame spreading angle were abstracted from the binarized image. The results showed that there existed a subtle flame flashback phenomenon for the flame base, whereas the flame spreading angle maintained a relatively constant value with a small deviation. The frequency-domain analysis revealed that both the flame base position and flame spreading angle reached the peak amplitude in the direct current component (0 Hz), exhibiting no explicit high-amplitude resonance component within 1500 Hz compared to those in the diffusion combustion mode. In all, the supersonic premixed flame presented a stabilized flame morphology.

Trajectory tracking control of a flexible air-breathing hypersonic vehicle using Lyapunov-based model predictive control

Considering the constraints of inputs and angle of attack (AOA), the trajectory tracking control of a flexible air-breathing hypersonic vehicle (FAHV) is investigated. To solve the problem, the Lyapunov-based model predictive control (LMPC) is presented. Firstly, the virtual controller is designed by nonlinear backstepping control (BSC), and it is integrated into the Lyapunov contraction constraint in LMPC to ensure the stability of the closed-loop system. Secondly, LMPC law is obtained by optimizing the weighted summation performance index of the tracking error and the control. Within the LMPC framework, the input constraints and AOA constraints can be handled simply, and by designing the appropriate parameters of the virtual controller, closed-loop stability is achieved. The effectiveness and superiority of the proposed method are verified by comparing it with the BSC and traditional model predictive control.

Research on the Zooming Method for Determining the Flow, Heat Transfer, and Infrared Radiation of an Air-Breathing Hypersonic Vehicle Powered by a Scramjet

In order to study the infrared radiation characteristics of an air-breathing hypersonic vehicle powered by a scramjet, it is necessary to solve the internal and external flow field of the air-breathing hypersonic vehicle. Owing to the complexity and difficulty of solving the three-dimensional flow and heat-transfer process in a scramjet combustor, a quasi-one-dimensional calculation method was established. Utilizing zooming technology, a combination of quasi-one-dimensional simulation within the combustion chamber and three-dimensional numerical simulation elsewhere on the vehicle was employed to obtain the flow field. The accuracy of the zooming method in determining flow, heat transfer, and infrared radiation was verified through comparison with experimental data. The results show that under the flight condition of Ma = 6, the gas temperature and wall heat flux in the scramjet combustor first increased and then decreased along the flow direction. The Mach number of the plume was smaller than that of the free flow, while the velocity of the plume was slightly larger. In the wavelength range of 3–5 μm, as the azimuth angle increased, the integrated radiation intensity of the air-breathing hypersonic vehicle demonstrated a characteristic pear-shaped distribution.

Longitudinal Air-Breathing Hypersonic Vehicle Nonlinear Dynamic Simulation with Different Control Inputs

<div>The air-breathing hypersonic vehicle (AHV) holds the potential to revolutionize global travel, enabling rapid transportation to low-Earth orbit and even space within the next few decades. This study focuses on investigating the nonlinear dynamic simulation, trim, and stability analysis of a three-degrees-of-freedom (3DOF) longitudinal model of a generic AHV for variable control surface deflection, <i>δ<sub>e</sub></i> and <i>δ<sub>r</sub></i>. A simulation is developed to analyze the burstiness of the AHV’s nonlinear longitudinal behavior, considering the complete flight envelope across a wide range of Mach numbers, from <i>M</i> = 0 to 24, for selected stable <i>M</i>. The presented simulation assesses trim analysis and explores the dynamic stability of the AHV through its flight envelope and bifurcation method analysis is carried out to gain insight and validate the dynamic stability using eigen value approach.</div>

Multi-objective optimization of a hypersonic airbreathing vehicle

Multi-objective optimization of a hypersonic airbreathing engine (scramjet technology) was carried out with the aim of maximizing thrust and minimizing drag while satisfying a series of design constraints, such as avoiding unstart (blockage of supersonic flow within the combustion chamber) by ensuring that the pressure ratio across the shock waves remains below the adverse pressure gradient given by the Korkegi limit, geometry correction to achieve shock on-lip condition, and temperature and pressure requirements at the inlet exit. Using the relations presented in the literature, pressure and viscous drag are estimated analytically. The analytical approach is verified against computational fluid dynamics data from Ansys Fluent to solve two-dimensional compressible Reynolds-averaged Navier–Stokes flow equations, with transition shear stress transport as the turbulence closure model. Comparing the total drag and the flow properties at the combustion chamber entrance shows the model's feasibility for the optimization approach. Three different approaches were conducted to formulate the multi-objective function to determine the one that can find the highest number of geometries satisfying the Korkegi limit with the highest net thrust. The best approach was the multi-objective function formulated with the uninstalled thrust, total pressure recovery, and pressure drag, concentrating the search in the region with greater uninstalled thrust and lower drag and nearly doubling the value of net thrust compared to the first formulation, which uses the uninstalled thrust, pressure drag, and viscous drag.

Preliminary design of a hypersonic airbreathing vehicle based on four steps: An academic approach to learning

This article proposes a systematic approach for the preliminary design of a hypersonic airbreathing (scramjet) vehicle within an academic context. The goal is to serve as an educational tool, focusing on teaching students the fundamental physical concepts behind scramjets. The article provides essential equations for generic scramjet designs while explaining the simplifications made from an academic perspective. It demonstrates the use of spreadsheets as a user-friendly tool to modify parameters and observe the behavior of shock waves. The article outlines a four-step procedure. It includes estimating atmospheric properties, designing the supersonic inlet, calculating combustion chamber parameters, and determining postcombustor properties. An academic exercise illustrates these steps for a scramjet flying at a specific velocity and altitude. The results show that this procedure, combined with spreadsheets, enables a rapid prediction of thermodynamic properties, enhancing the understanding of the fundamental physics behind hypersonic airbreathing vehicles.

Role of cavity in a Mach 8 axisymmetric scramjet combustor: Flame stabilization vs combustion enhancement

The cavity-assisted scramjet has been proven to be the most promising propulsion system for air-breathing hypersonic vehicles. In this paper, numerical simulations of a Mach 8 axisymmetric scramjet combustor are conducted and validated to investigate the effect of the cavity. The results indicate that the combustion state undergoes significant changes as the combustion heat release increases. Detailed analysis reveals that the role of the cavity in flame stabilization and combustion enhancement also changes with combustion heat release. Under weak heat release conditions, the high-speed environment results in reduced combustion efficiency, and the primary role of the cavity is to stabilize the flame. Increasing the cavity size does not yield significant gains but could bring redundant mass. As heat release intensifies, the combustion enhancement effect of the cavity becomes more prominent. The presence of the cavity dramatically improves fuel combustion efficiency. The distribution of supersonic and subsonic combustion modes, as well as that of premixed and diffusion combustion modes, is also affected by cavity size and combustion heat release. In the engineering development of scramjets, it is suggested that the design of the cavity flameholder should involve careful consideration of combustion heat release.

A novel ray method for the coking of n-decane in circular tubes with flexible cross-section area

Coking of endothermic hydrocarbon fuels significantly deteriorates the efficiency of regenerative cooling for hypersonic airbreathing vehicles. A novel ray method based on dynamic mesh techniques is proposed to describe the coking behavior in a circular tube with a flexible cross-section area. This method can be used to identify metal and deposit coke efficiently, which promotes the applicability of the dynamic mesh method in flexible structures. The cooling performance of n-decane before and after coking is numerically simulated and compared. The deposition brings higher thermal risks by elevating the solid temperature. However, the deposition reduces the channel’s cross-sectional area and increases the flow speed, leading to decreased flow residence time. Because the suppressing effect from lower flow residence time outweighs the promotion effect from increased temperature, the n-decane conversion decreased after coking.

Shock interactions and heating predictions on a V-shaped blunt leading edge at Mach 6–12

V-shaped blunt leading edges (VSBLEs) are usually found at the inlet lips of air-breathing hypersonic vehicles and irregular shape flows. In this work, the VSBLE flows are investigated using numerical simulations and theoretical analysis from Mach 6 to Mach 12. The simulation results show that complex shock–shock interactions around the VSBLE cause extremely high heat flux peaks, which nonlinearly increase with the freestream Mach numbers. To theoretically study the flow mechanism, the shock interactions are divided into large-scale primary shock interactions (PSIs) and micro-scale secondary shock interactions (SSIs). The PSIs are constant, but the SSIs experience a transition from Mach reflection to regular reflection with the Mach number increasing. A transition criterion for the SSIs is established by the shock interaction theory. Furthermore, the increase in the heat flux peaks is proved to be caused by the SSI transition. A semi-empirical heat flux prediction method that relates the shock intensity and heat flux amplification is established. Finally, the transition criterion and the heat flux prediction method are verified by simulations at higher Mach numbers and experiments of VSBLEs with different geometric parameters. This paper develops a theoretical analysis approach for quickly predicting the shock interaction types and heat flux peaks of the VSBLEs under a wide range of Mach numbers.

Event-triggered hierarchical learning control of air-breathing hypersonic vehicles with predefined-time convergence

Event-triggered hierarchical learning control of air-breathing hypersonic vehicles with predefined-time convergence

Aerodynamic analysis of an airframe-inlet integrated full-waverider vehicle designed by osculating cone theory

Recently proposed, the airframe/inlet integrated full-waverider vehicle design methodology introduces an innovative approach to the design of air-breathing hypersonic vehicles. This methodology, compared to traditional integrated waverider design methods, leverages the features of the waverider to enhance the compression ability of the precompression surface and the lift-to-drag ratio characteristics of the vehicle. However, existing full-waverider design methods, based on cone-derived waverider theory, result in a gas cross-flow phenomenon at the inlet lip due to the conical shockwave. This paper suggests an airframe/inlet integrated full-waverider vehicle design method that utilizes the osculating cone waverider theory to improve gas intake quality. Initially, we present the method to obtain profile lines and basic flow field models at different osculating planes of the vehicle. We then validate the osculating cone integrated full-waverider vehicle design methodology through computational fluid dynamics. Although the viscous effect slightly reduces the lift-to-drag ratio of the vehicle and the total pressure recovery coefficient at the isolator exit, the shock wave remains attached to the leading-edge. Finally, a comparison with the cone-derived integrated full-waverider vehicle reveals that the osculating cone integrated full-waverider vehicle achieves similar aerodynamic performance, but with superior gas intake quality. The results indicate that the methodology proposed herein holds promise for guiding future engineering applications of integrated full-waverider vehicles.

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.

Koopman-operator-based learning control of air-breathing hypersonic vehicles with nonminimum phase properties

In this article, a prescribed learning controller is developed for nonminimum phase air-breathing hypersonic vehicles (AHVs) in the presence of parametric uncertainties and external disturbances. In comparison with the current state of the art, the most significant feature of our control design lies in introducing the Koopman operator to construct an intelligent output redefinition to overcome the nonminimum phase behavior. To evaluate the current control behavior and enhance the learning ability, an improved continuous-time performance index is developed under the actor–critic learning structure. Furthermore, combined with a nonlinear disturbance observer, prescribed learning control is proposed to design control commands, while compensating for lumped disturbances, including neural approximation errors and external disturbances. Numerical simulations have been performed to highlight the superiority of the proposed learning control.

Similarity Analysis for Two-Dimensional Hypersonic Inlets Restart

The restart ability of inlets is significant to the robustness of hypersonic airbreathing vehicles. Classic starting theories based on the one-dimensional and inviscid flow assumption cannot predict the restart boundary accurately. To overcome the classic theories, the restart characteristics of two-dimensional contraction ducts in viscous flow are numerically studied. The restart boundaries for different configurations and flow conditions are determined, and the restart similarity laws are discovered. With the proposed dimensionless quantities (the dimensionless cowl length and the effective throat-entrance area ratio), the influences of multiple factors on restart are described simultaneously in a concise self-similar formulation. The restart characteristics can be described with any two variables in cowl angle, dimensionless cowl length, and effective area ratio. The restarts of two-dimensional inlets are classified into three types of the short-cowl, transitional, and long-cowl restarts according to the features of restart boundary lines and the flow structure. The three restart types are dominated by the competition between the cowl shock system and cowl tail expansion waves, the cowl shock system alone, and the complementation between the cowl shock system and throat choke, respectively. The wall pressure criteria for restart are correlated with the dimensionless cowl length and the characteristic separation scale at the restart critical state. It is observed that Kantrowitz limit is not generalizable for restart boundaries.

Performance Improvement of Kerosene Fuelled Scramjet Combustor Through Modified Fuel Injection - A Cfd Study

Full scale kerosene fuelled scramjet combustor of a hypersonic air-breathing vehicle is numerically explored for two different fuel injection systems. A commercial software CFXTASCflow has been used for the reacting flow computation within the combustor. Three dimensional Navier-Stokes equations are solved along with k-ε turbulence model to analyse the flow field. Eddy Dissipation Model (EDM) with fast rate chemical kinetics is used for combustion modeling. Lagrangian Particle Tracking Method (LPTM) has been used to simulate the trajectory of the kerosene droplets. Kerosene is injected from the struts. Reacting flow simulations have been carried out for the fuel equivalence ratio of 1.0. The overall flow characteristics in the combustor are presented through the distribution of various thermochemical parameters at different cross sections. Kerosene which is injected in liquid phase completely vaporizes within the combustor. Considerable improvement in the performance in terms of thrust and combustion efficiency is observed with the modified fuel injection system.

Reliability analysis for air-breathing hypersonic vehicles based on a new dynamic PHI2 method

Purpose This paper aims to present a novel dynamic reliability model that considers the interval mixed uncertainty for the air-breathing hypersonic flight vehicle (AHFV) to guarantee flight safety and structural reliability. Design/methodology/approach Initially, the force condition of the fuselage is analyzed based on the longitudinal elastic model of an AHFV. Subsequently, a new high-efficiency dynamic reliability model is presented to describe the failure probability evolution of the fuselage structure. For the random uncertainty problem with interval distribution parameters, the interval PHI2 method of time-dependent reliability is used to obtain the time-dependent reliability interval of the AHFV. Finally, the key variables that affect the failure probability accumulation are determined, which provide an important reference for ensuring structural reliability and improving the life span of AHFVs. Findings It is demonstrated that the proposed reliability model can obtain more accurate dynamic reliability results for the fuselage, and it is confirmed the key variables that affect the failure probability accumulation. The results also provide an important reference for the reliability analysis of hypersonic vehicles. Originality/value The novelty of this work comes from the first application of the PHI2 method (considering the interval mixed uncertainty) in the AHFV and the development of a new reliability model for the entire body of AHFVs. The proposed analysis scheme is implemented on the dynamic model of the AHFV, which provides a more accurate reference for improving the structural reliability and life span of AHFVs.

Preventing inlet unstart in air-breathing hypersonic vehicles using adaptive backstepping control with state constraints

Aiming at the problem that the inlet is prone to unstart during the flight of air-breathing hypersonic vehicles (AHV), an adaptive backstepping control method with state constraints is proposed to prevent the occurrence of inlet unstart. Firstly, a parametric model of AHV with velocity, flight path angle, angle of attack and angle of attack rate as state variables is derived. Then, adaptive dynamic inverse control is adopted for the velocity subsystem, and adaptive backstepping control with state C is adopted for the flight path angle subsystem. The tracking errors of angle of attack and angle of attack rate are constrained by asymmetric barrier Lyapunov function (ABLF) and symmetric barrier Lyapunov function (SBLF) respectively, and smooth saturation function is constructed to restrict the virtual control commands. Adaptive laws are used to handle parameter uncertainty. Finally, it is proved by Lyapunov theory that the states of the closed-loop system can be uniformly and ultimately bounded, and the constraints on angle of attack and angle of attack rate can be satisfied. The simulation results show that compared with the adaptive backstepping control method, the proposed method can guarantee that the angle of attack and angle of attack rate are always within the operating limits of scramjet engine, and effectively avoid the occurrence of inlet unstart.

The determination of physical dimensions of a hypersonic three-stage compression system considering panel vibration effects

The panel vibration of air intake system that excitated by fluid-structural interaction, engine thrust variation and noise has decisive influences on the performance of an air-breathing hypersonic vehicle. The design of such type of intake system should contain the determination of configurational parameters and physical dimensions by considering both flow and structural vibrations, and a clear design path is still absent. In this paper, an intake system with three-stage external compression ramps is designed under Mach number of 6 and flight altitude of 24 km, and the configurational parameters are determined based on the shock-on-lip criterion, Oswatitsch criterion and viscous effects modification. The mode vibration characteristics of external compression ramps with panel thicknesses of 0.002 to 0.03 m are analyzed, and appropriate natural frequencies are obtained by constraint conditions of fixed four side boundaries with an additional and more realistic constraint of strengthened internal boundary. The flow field of the intake system with forced panel vibrations of compression ramps is simulated, and the effects of vibration amplitude of 0 to 0.11 m and frequency of 10 to 250 Hz on the intake performance, i.e., total pressure recovery coefficient and mass flow coefficient are clarified. The vibration effects of hypersonic flow on the compression ramp structure and intake performance are studied by fluid-structural coupling simulations. Finally, the available physical dimensions of external compression ramps are determined and a design path of intake system is developed by considering both the structural and intake performance.

Dynamic Transition of Unsteady Supersonic Flow From Mach to Regular Reflection Over a Moving Wedge

Abstract The design of supersonic and hypersonic air-breathing vehicles is influenced by the transition between the Mach reflection (MR) and regular reflection (RR) phenomena. The purpose of this study is to investigate the dynamic transition of unsteady supersonic flow from MR to RR over a two-dimensional wedge numerically. The trailing edge of the wedge moves downstream along the x-direction with a velocity, V(t) at a freestream Mach number of 3. An unsteady compressible inviscid flow solver is used to simulate the phenomenon. The Arbitrary Lagrangian–Eulerian (ALE) technique is applied to deform the mesh during the wedge motion. The dynamic transition from MR to RR is defined by two criteria, the sonic and the von Neumann. Moreover, the lag in the dynamic transition from the steady-state condition is studied using various nondimensional angular velocities, κ, in the range of [0.1-2]. The lag effect in the shock system is remarkable at the high values of κ greater than 1.5. Furthermore, the dynamic transition from MR to RR happens below the dual solution domain (DSD) because the shock is upstream curved during the wedge motion.