超声速平板边界层中流向涡的生成条件

针对马赫数为4.5的超声速平板边界层，基于线性稳定性理论（LST）选取初始扰动组合，通过直接数值模拟（DNS），计算了第一模态不稳定波扰动组合沿流向演化生成流向涡的过程。采用改进Omega-Liutex旋涡识别方法进行涡识别，结合流向不同位置截面的流线图，分析了流向涡的生成特性。根据流向涡在zy截面内的流线特征，提出了流向涡的生成条件，研究发现:流向涡可以直接通过一对展向对称的第一模态不稳定斜波扰动与基本流叠加得到，不是必须经过非线性作用。 

Generation conditions of streamwise vortex in supersonic flat-plate boundary layer

The initial disturbance combinations were selected based on the linear stability theory （LST） for a supersonic flat-plate boundary layer with Mach number of 4.5.Through direct numerical simulation （DNS），the generation process of streamwise vortex due to the evolution of combined first-mode unstable waves along the flow direction was simulated.Based on the vortex identification method of modified Omega-Liutex and the streamline diagram at different positions in the streamwise direction，the generation characteristics of streamwise vortex were analyzed，and its generation conditions were proposed according to the features of streamline in zy plane.It was found that streamwise vortex can be obtained directly by superimposing a pair of first-mode unstable oblique waves and basic flow，in which nonlinear action was not necessary.