高超声速椭圆锥边界层横流转捩特性大涡模拟

横流效应显著影响高超声速飞行器的三维边界层转捩过程, 深化对该流动机制的认识有助于提升和改善飞行器气动性能及热力学环境. 针对HIFiRE5椭圆锥绕流问题, 采用大涡模拟方法计算分析了超声速边界层横流转捩特性, 并揭示其中的流动机理. 参考HIFiRE5风洞模型试验条件, 数值模拟中椭圆锥来流入口处施加人工速度扰动以激发边界层内不稳定扰动波, 进而预测了高超声速边界层流动横流失稳、转捩过程等基本流动特征, 并基于转捩热流分布形态对比, 获得了与试验数据基本吻合的计算结果. 研究发现, 椭圆锥中心线流动汇聚形成的流向涡结构非常容易失稳, 另外在中心线及侧缘之间的中部区域存在较强的横流不稳定性, 两种机制共同作用影响边界层转捩过程. 此外, 分析了来流扰动幅值对边界层横流失稳转捩的影响, 并发现静来流条件下, 横流区域出现两组独立的定常横流涡结构, 而强噪声来流条件下, 中心线主涡和中部横流涡均发生失稳转捩, 且在椭圆锥表面形成多峰状的转捩阵面. 最后, 深入分析流场的压力脉动动力学特性, 揭示了三维边界层发生失稳转捩的非线性演化机制. 

Large Eddy Simulation of Crossflow Transition Characteristics in Hypersonic Elliptic Cone Boundary Layer

The crossflow effect significantly affects the three-dimensional boundary layer transition process of hypersonic vehicle. Deepening the understanding of the flow mechanism is helpful to improve the aerodynamic performance and thermodynamic environment of hypersonic vehicle. Aiming at the flow around HIFiRE5 elliptic cone, the characteristics of cross-flow transition in supersonic boundary layer were calculated and analyzed by using large eddy simulation method, and the flow mechanism was revealed. Referring to the HIFiRE5 model test conditions of wind tunnel, in the numerical simulation, an artificial velocity disturbance was applied at the inlet of the elliptic cone to excite the unstable disturbance wave in the boundary layer, and then the basic flow characteristics such as crossflow instability and transition in the hypersonic boundary layer were predicted. Based on the comparison of transition heat flow distribution, it was proved that the calculation results were basically consistent with the experimental data. It is found that the streamwise vortex structure formed by the flow convergence on the center line of the elliptic cone is very easy to become unstable. In addition, there is a strong crossflow instability in the middle region between the center line and the side edge. The two mechanisms affect the boundary layer transition together. Furthermore, the influence of the amplitude of the inflow disturbance on the crossflow instability transition in the boundary layer was analyzed. It is found that under the quiet inflow condition, two groups of independent steady crossflow vortex structures appear in the crossflow region, while under the noisy inflow condition, the instability transition occurs in the main vortex of the centerline and the middle crossflow vortex, and a multi-peak transition front is formed on the surface of the elliptic cone. Finally, the dynamic characteristics of pressure fluctuation in the flow field were deeply analyzed, and the nonlinear evolution mechanism of instability transition in three-dimensional boundary layer was revealed.