时间发展平面混合流的三维演化

采用高精度差分方法和群速度控制方法，求解三维可压缩Ｎ Ｓ方程，直接数值模拟了时间发展的平面混合流．研究了平面混合流三维拟序结构的形成及发展．给出了流动失稳后涡的卷起，相邻两涡的对并，激波的形成及发展．指出，涡对并所诱导产生的激波对三维拟序结构的形成及发展过程是重要的．

DIRECT NUMERICAL SIMULATION OF THREE DIMENSIONAL TEMPORALLY EVOLVING COMPRESSIBLE MIXING LAYER 1)

The three dimensional temporally evolving compressible mixing layer is simulated directly with the Navier Stokes equations. The discretization method has high order accuracy with group velocity control. The viscous terms of the equations are discretized with the sixth order accurate symmetrical compact difference method, the convection terms are discretized with the fifth order accurate upwind compact difference approximation, and three stage Runge Kutta method is used in advance of time. The time developing mixing layer develops from specified initial conditions. They are obtained from mean streamwise hyperbolic tangent profile plus perturbations. Periodic boundary conditions are used in streamwise and spanwise directions, and nonreflection boundary condition is used in the normal direction. In computation the convection Mach number M c =0.8 and Re =600 (based on the initial vorticity thickness) are used. The process of loss of stability, vortex rolling up, vortex pairing and formation of the shocks are presented. It is shown that the shocks induced by vortex pairing are important in formation and development of the coherent structures in the compressible mixing layer.