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2024, Volume 9,  Issue 2

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Cover and contents of Vol.9 No.2
2024, 9(2): .
15 0
Abstract:
Heat Transfer Characteristics of Gap Flows in Shock-Wave Interference Region of Hypersonic Vehicles
LI Zongyang, DOU Yibin, REN Zhiyi, LU Yunchao, CHEN Junming
2024, 9(2): 1-8. doi: 10.19527/j.cnki.2096-1642.1100
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Abstract:
In view of the heat transfer problems of gap flows near the shock-wave interference region of hypersonic vehicles, a two-dimensional model of the shock generator and gap was established. By using CFD technology, the internal flow heat transfer characteristics with shock waves in the front, middle and back of the gap were studied. The results showed that compared to the flow fields without shock wave, the vortex structure of the flow inside the gap changes obviously when the shock wave acts on the front and middle of the gap, resulting in a sharp increase in the flow intensity and heat inside the gap. However, when the shock wave acts on the rear part of the gap, the vortex structure inside the gap does not change significantly, and the far-end wall heat flux near the gap lip decreases locally, which is beneficial to the shape protection of the thermal protection structure. The results clearly indicated that it is necessary to avoid the position where shock wave acts on the front and middle part of gap in structural thermal protection design.
Effects of Mach Number and Wall Temperature on HyTRV Boundary Layer Transition
ZHANG Luxing, WANG Guangxue, DU Lei, YU Fayuan, ZHANG Huaibao
2024, 9(2): 9-20. doi: 10.19527/j.cnki.2096-1642.1098
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Abstract:
There is a complex transition phenomenon in the flow field of a typical hypersonic vehicle, which has a significant impact on the performance of the vehicle. The effects of Mach number and wall temperature on the transition of HyTRV were studied by numerical simulation methods. The self-developed software of the research group was used to carry out numerical calculations. The range of Mach number was 3~8, and the range of wall temperature was 150~900 K. Firstly, the hypersonic corrections of the γ-$\mathop R\limits^ \sim $eθt transition model and the SST turbulence model were carried out. The pressure gradient coefficient correction and the high-speed cross-flow correction were introduced into the γ-$\mathop R\limits^ \sim $eθt transition model, and the compressibility corrections of the closure coefficients β* and β of the SST turbulence model were carried out. Then, the grid independence verification was carried out, and the modified numerical method and software platform were confirmed by comparing with experimental results. Finally, the effects of Mach number and wall temperature on the transition law of the HyTRV boundary layer were studied. The results show that the transition area is mainly concentrated on both sides of the upper surface and the center line of the lower surface. With the increase of the incoming Mach number, the starting position of transition on the upper and lower surfaces is greatly backward, and the turbulent zone is greatly reduced, but it still exists. At the same time, the friction coefficient of the laminar flow zone on the upper surface increases continuously, and the friction coefficient of the turbulent zone on the lower surface decreases. As the wall temperature increases, the starting position of transition on the upper and lower surfaces shifts forward, then rapidly shifts backward, and finally the turbulent zone almost disappears.
Rotating Detonation Combustion Characteristics of Kerosene-Fueled Wide-Area Scramjets
SHU Chen, GU Futao, CHEN Bin, YAN Chenglong, TONG Yiheng, LIN Wei
2024, 9(2): 21-32. doi: 10.19527/j.cnki.2096-1642.1082
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Abstract:
Through the method of three-dimensional numerical simulation, the rotating detonation combustion characteristics of kerosene-fueled scramjets in the range of Ma＝3~7 were studied. In the flight condition of Ma=3, due to the poor effect of fuel atomization and evaporation, the detonation combustion of kerosene fuel cannot be realized. In the flight conditions of Ma＝4, 5, 6, with the increase of Mach number, the number of wave heads increases gradually, which are single-wave, three-wave, and five-wave modes, respectively. However, the propagation speed gradually decreases. In the scramjet mode, the liquid fuel has a good effect of atomization and evaporation. Nevertheless, kerosene vapor remains in the flow field to varying degrees and is discharged from the combustion chamber without participating in the reaction. In the flight condition of Ma＝7, the flow field will burn in a stationary detonation mode because the incoming flow is close to CJ velocity.
A Simplified Neural Network Model for Compressible Two-Gas Flows
LIU Ziyan, XU Liang, LIU Yaofeng
2024, 9(2): 33-42. doi: 10.19527/j.cnki.2096-1642.1089
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Abstract:
The practical ghost fluid method (PGFM) utilizes velocity solutions of Riemann problems to model the interface evolution of compressible multi-material flows. This paper presented a simplified neural network model for two-gas flows by predicting the velocity solution of Riemann problem based on the neural network model embedded with physical constraints. Firstly, a method for converting the sampling range of the neural network model from unbounded domain to bounded domain was proposed, which holds true for the perfect gas equation of state. It can improve the generalization performance of the model under different initial conditions. Based on this transformation method, a simpler neural network structure was further proposed. The training result of the neural network can be effectively improved by reducing the input dimensions from 5 to 3. The neural network model was applied to the PGFM. Numerical validation of the neural network model was carried out through typical one-dimensional and two-dimensional gas flow problems. The results show that the simplified network model can achieve similar computational accuracy compared with existing neural network models. In terms of training efficiency of neural networks, the simplified neural network has obvious advantages. Moreover, because the simplified neural network has fewer sampling dimensions, it is convenient to try denser sampling to improve fitting accuracy and such method has more development potential.
Aerodynamic Modeling and Path Optimization of Wing Docking Process for Fixed-Wing UAVs
CHEN Yiwei, LIU Haojie, HUANG Rui, GAO Xiumin
2024, 9(2): 43-53. doi: 10.19527/j.cnki.2096-1642.1084
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Abstract:
The problem of aerial docking of fixed-wing UAVs restricts the development of the chained-wing UAVs. The aero-dynamic modeling and path planning of the wing docking process of fixed-wing UAVs were investigated. At first, the aerodynamic model of the wing docking process of fixed-wing UAVs was established by using the numerical lifting-line theory. The aerodynamic coupling effects of the UAVs at different relative positions were analyzed. Then, the path planning of the wing docking process was considered as a weighted directed shortest path problem. The optimal wing docking path was obtained by using the path planning method based on the Dijkstra algorithm. Numerical simulation results demonstrate that the aerodynamic modeling method can reliably describe the aerodynamic coupling effects during the wing docking process. The optimal wing docking path significantly reduces the wingtip vortex interaction.
Wing Design and Adaptive Optimization of a Compound Drone
ZHANG Wei, TAN Meng, LIU Yafeng, NIE Yongbin, LUAN Yue
2024, 9(2): 54-65. doi: 10.19527/j.cnki.2096-1642.1091
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Abstract:
With the growing demand for unmanned transportation, the rise of compound drones is imperative. Aerodynamic optimization design plays a significant role in the development cycle of compound drones. Researches were performed on key parameter adaptive screening and design space adaptive updating of surrogate-based aerodynamic optimization techniques. A parametric/spatial adaptive aerodynamic optimization platform was established, which can improve the optimization efficiency and search capability effectively in the process of aerodynamic optimization. A preliminary design scheme of wing for a compound drone was presented, and adaptive aerodynamic optimization was carried out. The lift-to-drag ratios of the optimized wing root and tip airfoils and the resulting optimized wing were all increased by over 5%, with design lift coefficients equaling to 1.0, and the corresponding angles of attack were also reduced by more than 2°. The stall characteristics and the roll control ability of the wing were improved simultaneously.
Effect of Wavy Wall on the Stability of Conical Hypersonic Boundary Layer at Small Angle of Attack
ZHANG Chengjian, GUI Yuteng, LI Xueliang, CHENG Jiangyi, WU Jie
2024, 9(2): 66-80. doi: 10.19527/j.cnki.2096-1642.1078
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Abstract:
In order to obtain a high lift-drag ratio, hypersonic vehicles usually fly with a certain angle of attack. As a potential means to delay hypersonic boundary layer transition at 0° angle of attack, it is not clear how wavy wall affect the deve-lopment of instability waves with angles of attack. In order to study the influence of wavy wall on the development of instability waves in hypersonic boundary layer at small angle of attack, the stability of boundary layer was studied by adopting high-speed infrared camera and high-frequency pressure sensor (PCB) in Mach 6 Ludwieg tube wind tunnel. The development of instability waves along different azimuths and flow directions was analyzed. The experimental results show that the instability waves leading transition at 1° angle of attack are the second-mode waves. Under the condition of 1° angle of attack, the wavy wall has no delay effect on transition at 45° azimuth angle, but has a promotion effect at 90°, 135° and 180° azimuth angles.

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