Search

This study investigated the thermal protection performance of an active jet thermal protection system (PRsAJ-TPS) based on a new jet design parameter PRs for hypersonic flight vehicles (HFVs). The new parameter PRs is defined as the relationship between the jet flow total pressure and the free flow total pressure behind the outer bow shock. A 20° tilted nozzle design is employed together with the PRs to form the PRsAJ-TPS. Theoretical and numerical analysis is performed to prove the advantages of using the PRs. A conventional in-house CFD solver with the k ‐ ω SST turbulence model is utilized to perform the calculation. The influence of different PRs (working in the short penetration mode) and flight angles of attack on the performance of the PRsAJ-TPS is also studied. The simulation results confirmed that with a constant PRs, the Mach disk location stays the same and the normalized heat flux reduction is similar at different flight conditions. Nearly linear relationships exist between the new design parameter PRs and thermal protection performance indicators. The PRsAJ-TPS also exhibits good protection when flight angle of attack (AoA) varies between 0° and 40°, with the best results achieved at AoA = 0 ° . This study provides valuable information for the engineering application of the jet-based TPS to future HFVs. [ABSTRACT FROM AUTHOR]

In this work, a new configuration of strut-based scramjet is proposed, and a series of simulations are conducted to investigate its possibility of practical application. The simulation results are verified via the classical DLR ramjet and an experiment conducted on the connected pipe facility. The inlet area ( A in ) and air intake height (H) of the combustor are varied independently to investigate their performance. The results indicate that the flow field and shock wave structure of such engine reveal similar characteristics as the classical DLR engine, and the variation in engine geometry can significantly affect its combustion characteristics. Moreover, the combustion efficiency could be enhanced by 2% as the A in varied from 900π mm2 to 1100π mm2; increasing the air intake path (H) to 12 mm can increase the combustion efficiency by 25%. In general, the present work proposes a new geometry of the scramjet combustor; this combustor has possibility of practical application, but a further and detailed investigation is still needed. [ABSTRACT FROM AUTHOR]

In this study, the fatigue life prediction in hypersonic vehicle noise environment is researched under the structural vibration caused by the engine jet noise and the aerodynamic noise. A finite element analysis model is first established, and then natural frequency and vibration mode are obtained. According to the modal analysis, the vibroacoustic coupling calculation is finished in the dynamic analysis software. Modal participation factor, modal displacement, and the power spectral density of the stress response on the coupled surface are acquired. The finite element, border component, and vibrating stress analytical techniques are also employed in this research to predict the acoustical fatigue performance of the tail fins of a specific type of spacecraft. On the basis of vibration fatigue theory, identified material S–N curve, and linear cumulative damage theory, the Dirlik model in the frequency domain method for vibration fatigue is used to predict the fatigue life of empennage. According to the characteristics of the acoustic load, effects of the load characteristics, and damping ratios on the fatigue conditions, the design of the antifatigue design is put forward. [ABSTRACT FROM AUTHOR]

A grid fusion lifting surface suitable for large subsonic angles of attack was designed. The influence of the grid position, grid diversion angle, and grid number on the aerodynamic performance of the grid fusion lifting surface under subsonic conditions was studied by numerical simulations. Based on the summary and analysis of the grid in the hypersonic state, the CFD numerical simulation method, which solves unsteady Reynolds averaged Navier-Stokes equations, was used to complete the research of the flow mechanism of the grid fin in the subsonic state. At low speed and subsonic conditions, the results show that the negative front grid fusion lift surface has better aerodynamic characteristics with a high angle of attack. Under subsonic conditions, the stall angle of attack of the front grid fusion lifting surface with a diversion angle of 20° increases by 16°, and the maximum lift coefficient increases by 22.1% compared to that of the conventional flat wing. The number of grids has an insignificant effect on the aerodynamic performance of the grid fusion lifting surface at a large angle of attack. [ABSTRACT FROM AUTHOR]

In the descent phase of the hypersonic target flight trajectory, the hypersonic speed of the target makes the reaction time shorter. Due to overload restrictions, it is challenging for the interceptor to achieve successful interception. To address this problem, a predictive differential game guidance approach based on dynamic optimization algorithm is proposed to relax the interceptor acceleration requirements. Two-dimensional kinematics and dynamics engagement mode for hypersonic target interception is formulated as a nonlinear differential control model in the presence of matched uncertainties. The nonlinear differential model is transformed into a differential game model by combining a performance index. The performance index is positively correlated with the Line-Of-Sight (LOS) rate and control effort of interceptor and negatively correlated with the target maneuver. The Chaotic Quantum Particle Swarm Optimization (CQPSO) algorithm is utilized to address the nonlinear differential game problem to generate the instantaneous and predicted guidance commands for the interceptor and target. Numerical examples are given to verify the performance of the proposed guidance law in various engagement scenarios, including different target maneuvers, initial heading angles and target overload. Moreover, the performance of the algorithm is validated comparing with traditional and state-of-the-art guidance laws. [ABSTRACT FROM AUTHOR]

In order to investigate the dynamic characteristics of blunt aircraft mounted with aerospikes and aerodisks in large-amplitude force-pitching, the Roe spatial scheme and the lower-upper symmetric Gauss-Seidel (LU-SGS) method with dual time step are employed for discretization of unsteady Navier-Stokes (N-S) equations. A parametric investigation on the flow fields is conducted by altering the pitching period, aerospike length, and aerodisk diameter consequently via a variable-controlling procedure. Dynamic characteristics of aerodynamic drag as well as the visualization of unsteady flow fields are achieved, and the results show that the aerodynamics of hypersonic aircraft under the condition of large-amplitude force-pitching vibration have hysteresis characteristics affected by periods of force-pitching vibration. In addition, when changing aerospike length and aerodisk diameter, the variation tendency of drag reduction efficiency is determined by the pitching angle of the oscillation process. [ABSTRACT FROM AUTHOR]

The selection of an appropriate turbulence/transition model is critical when simulating the hypersonic flows based on the Reynolds-averaged Navier–Stokes (RANS) equation. In particular, a deep understanding of the validity, reliability, and limitations of existing models is an essential prerequisite to facilitate their further development. This paper reports on the assessment of two models dedicated to hypersonic boundary layer transition analysis. Both models are compared with two other models that are widely used in this field. The double ramp and shock wave laboratory scramjet intake cases are used for the validation and evaluation of the predictive performance of both models via comparison against experimental data. The results reveal that the appropriate selection of the transition model is critical to the attainment of accurate results. Moreover, the forebody of the scramjet combustion propulsion-01 (SCP-01) flight vehicle, which is a research model, is analyzed as a case study. The air intake performance of the SCP-01, as predicted by four models, is compared and analyzed at different flight altitude and Mach number conditions. The results reveal that the accuracy of the prediction of boundary layer and separated flow transitions significantly affects the flow field and corresponding air intake performance. Furthermore, the uncertainty of results obtained using the two models increases significantly with an increase in altitude. Finally, the reliability and limitations of the transition models considered in this study are examined. [ABSTRACT FROM AUTHOR]

An axisymmetric model scramjet assisted with cavity flameholder is numerically investigated. Three-dimensional Reynolds-averaged Navier-Stokes simulation is carried out to reveal the fuel mixing and combustion characteristics. The simulation results show reasonable agreements with experimental data. The analysis indicates that the axisymmetric and rectangular scramjet has some similarities to the cavity shear layer in the nonreacting flow field. The configuration of the cavity shear layer changes hugely due to the significant chemical reaction and heat release in the reacting flow field. Typically, two more configurations with different cavity aft wall angles are compared with the experimental configuration to optimize the configuration of the cavity. When the cavity aft wall angle is small, the cavity shear layer bends to the cavity floor and more fuel enters into and stays in the cavity, which results in poor fuel mixing performance. With the increase of the aft wall angle, the fuel distributes more uniformly and the fuel mixing efficiency improves. In the reacting flow field, the volume of the cavity full of hot products and free radicals increases while the interaction between the cavity and main flow decreases with the increase of the aft wall angle. The improved combustion efficiency shows that larger cavity volume weighs more than reduced interaction between the cavity and main flow. The combustion is more violent in the case with a larger aft wall angle. Therefore, a proper increase of the aft wall angle is beneficial to the performance of cavity-assisted axisymmetric scramjet when designing the cavity flameholder. [ABSTRACT FROM AUTHOR]