Zhenxun Gao

Bio: Zhenxun Gao is an academic researcher from Beihang University. The author has contributed to research in topics: Boundary layer & Supersonic speed. The author has an hindex of 11, co-authored 60 publications receiving 394 citations. Previous affiliations of Zhenxun Gao include National Laboratory for Computational Fluid Dynamics & China Aerospace Science and Technology Corporation.

Numerical research on mixing characteristics of different injection schemes for supersonic transverse jet

Abstract: A numerical method using AUSMDV scheme and k-ω SST turbulence model with an explicit compressibility correction was developed, and a 3-D numerical simulation of a supersonic flow field with a vertical sonic jet of hydrogen was performed Good agreement between numerical results and experimental data validated the reliability of the numerical method Whereafter, two parameters, mass-weighted average total pressure and mixing efficiency, were defined to evaluate the mixing performance of different injection schemes Based on the numerical method and evaluation criterion, the mixing characteristics of different injection schemes were studied in detail It was found that for the mixing field of supersonic transverse jet, the near-field mixing is controlled by convection transport while the far-field mixing is controlled by mass diffusion; the circular-hole injection causes a loss of total pressure comparable to the slot injection, but can induce a much higher mixing efficiency because of its 3-D flow characteristic; the variation of injection angle under circular-hole injection mainly affects the near-field mixing degree, and among the five injection angles studied in the present paper, angle 120° is the optimal one; with the increase of the ratio between injector space and diameter, the induced mixing efficiency increases while the caused loss of total pressure can grow greatly; the two-stage injection method designed through reducing the injector area to keep the same hydrogen mass flowrate can induce a much higher mixing efficiency while only a bit larger loss of total pressure when compared to the single-stage injection, and hence the two-stage injection is superior to the single-stage injection The research results can direct the design of the fuel injection method in the combustor of scramjet engine

Combustion Heat-Release Effects on Supersonic Compressible Turbulent Boundary Layers

Abstract: Influences of heat release by the hydrogen combustion in supersonic turbulent boundary layers are numerically studied using Reynolds-averaged Navier–Stokes equations. The adopted Reynolds-averaged Navier–Stokes methodology is first validated by comparing the numerical results with the existing experimental data. Studies on the effects of the flame perpendicular position inside the boundary layer reveal that, while the flame is restricted around the edge of the boundary layer, the heat release may slightly reduce rather than increase the wall heat flux because of the suppression effect on the turbulent energy transport due to heat release. However, as the flame moves toward the wall, the skin-friction reduction effect would not be obviously strengthened, but the wall heat flux could be dramatically enhanced by the increase of near-wall chemical reactions. At a given hydrogen mass flow rate, the injection scheme with a higher injection height and a lower injection velocity could be helpful to achieve a larg...

A numerical study of turbulent combustion characteristics in a combustion chamber of a scramjet engine

Abstract: 3D numerical simulation of flow fields in a combustion chamber of a scramjet engine using an SST turbulence model with an explicit compressibility correction was performed and the results were compared to the experimental results. The characteristics of the turbulent combustion flow fields were analyzed via the numerical results and presented. In order to identify the mechanisms of turbulent combustion in supersonic flows, the evolutions of governing dimensionless parameters in the flow fields were investigated based on the theory of combustion and the available numerical results. It was found that the supersonic combustion takes place in the region of fully developed turbulence and that the strongest effects of turbulence and combustion processes appear in the vicinity of the injector. The unsteady effects and the local flame extinction phenomenon induced by turbulent flows were found to be negligibly small, and the steady flamelet approximation will hold for practical applications.

Improvement and application of wall function boundary condition for high-speed compressible flows

Abstract: In order to develop a wall function boundary condition for high-speed flows so as to reduce the grid-dependence of the simulation for the skin friction and heat flux, a research was performed to improve the compressible wall function boundary condition proposed by Nichols. Values of parameters in the velocity law-of-the-wall were revised according to numerical experiments and the expression of temperature law-of-the-wall was modified based on theoretical analysis and numerical simulation. Besides, the formula of the heat conduction term in near-wall region was derived so that the coupling between the wall function boundary condition and CFD code was realized more accurately. Whereafter, the application study of the modified wall function was carried out. The numerical case of supersonic turbulent boundary layer on a flat plate illustrated that the modified wall function produces reasonable results of skin friction and heat flux, and profiles of velocity, temperature and turbulent eddy viscosity for coarse grids with the initial wall spacing of y+<400, and that the modifications to the original wall function can obviously improve the simulation precision. As for the application of separation flows, it was found from the numerical cases of supersonic cavity flow and hypersonic axisymmetric compression corner that the compressible velocity law-of-the-wall originally established based on the fully-developed attached turbulent boundary layer approximately holds in the near-wall region inside the separation flows, which ensures that reliable skin friction and heat flux can be given by the wall function inside the separation flows, while for the region near separation and reattachment points, the wall function gives results with a relatively large error, because the velocity law-of-the-wall used in the wall function takes on obvious deviation from the real velocity profiles near the separation and reattachment points.

Detached—Eddy Simulation方法模拟不同类型翼型的失速特性

Abstract: 应用DES(Detached-Eddy Simulation)方法数值模拟了3种不同失速类型的翼型的升力特性.DES方法结合了RANS(Reynolds-averaged Navier-Stokes)和LES(Large Eddy Simulation approaches)的优点.基于Spalart-Allmaras湍流模型,在近壁面DES体现为RANS模型的特点而在远离物面处又具有LES的亚格子模型的特性.对此模型使用了LU-SGS隐式格式求解.通过和实验结果对比,显示这种方法可以有效地预测翼型的失速特性.

Review of research on high-speed railway aerodynamics in China

Abstract: High-speed railway aerodynamics is the key basic science for solving the bottleneck problem of high-speed railway development. This paper systematically summarizes the aerodynamic research relating to China’s high-speed railway network. Seven key research advances are comprehensively discussed, including train aerodynamic drag-reduction technology, train aerodynamic noise-reduction technology, train ventilation technology, train crossing aerodynamics, train/tunnel aerodynamics, train/climate environment aerodynamics, and train/human body aerodynamics. Seven types of railway aerodynamic test platform built by Central South University are introduced. Five major systems for a high-speed railway network—the aerodynamics theoretical system, the aerodynamic shape (train, tunnel, and so on) design system, the aerodynamics evaluation system, the 3D protection system for operational safety of the high-speed railway network, and the high-speed railway aerodynamic test/computation/analysis platform system—are also introduced. Finally, eight future development directions for the field of railway aerodynamics are proposed. For over 30 years, railway aerodynamics has been an important supporting element in the development of China’s high-speed railway network, which has also promoted the development of high-speed railway aerodynamics throughout the world.

Progress in research on mixing techniques for transverse injection flow fields in supersonic crossflows

Abstract: The transverse injection flow field has an important impact on the flowpath design of scramjet engines. At present a combination of the transverse injection scheme and any other flame holder has been widely employed in hypersonic propulsion systems to promote the mixing process between the fuel and the supersonic freestream; combustion efficiency has been improved thereby, as well as engine thrust. Research on mixing techniques for the transverse injection flow field is summarized from four aspects, namely the jet-to-crossflow pressure ratio, the geometric configuration of the injection port, the number of injection ports, and the injection angle. In conclusion, urgent investigations of mixing techniques of the transverse injection flow field are proposed, especially data mining in the quantitative analytical results for transverse injection flow field, based on results from multi-objective design optimization theory.