【摘要】 采用高精度迎风／对称紧致混合差分算法，对可压自由剪切层转捩区中的几种典型展向 大尺度涡作用型态进行了直接数值模拟．通过施加给定来流条件下的线性最不稳定动性基频扰 动及其亚谐扰动，以被动守恒标量技术给出了基频涡卷的饱和、撕裂、融合以及三涡对并等细 节结构．分析显示，亚谐扰动相差是促生基频涡卷不同非线性演化过程的重要因素之一，可对 扰动能量的发展变化，以及剪切层厚度和混合效率产生直接影响．计算结果同实验流动显示图 像十分相似，表明了主导线性扰动的非线性耦合效应与一些实际涡作用行为间的内在联系．更多还原

【Abstract】 Several prototype flows typical of the spanwise large-scale rolluop interactions are investigated through using the direct numerical simulation method. These phenomena have been captured experimentally in the transition region of the free shear layer for a long time. A highaccuracy upwind/symmetric compact difference hybrid method is developed and is used to solve the two-dimenmsional compressible Navier-Stokes equations. A fifth-order upwind compact scheme is employed to discretize the convective flux terms with the help of the Sieger-Warming flux- splitting technique, while a sixth-order symmetric compact scheme obtained by Collatz is selected to discretize the transport flux terms. The three-stage third-order explicit Runge-Kutta algorithm found by Wray is introduced for time-marching. The temporally-developing compressible shear layer is disturbed by the most-unstable viscous wave and its subharmonic modes obtained numerically by linear stability analysis. The fine-scale struCtures of primar vortex saturating, tearing, merging, and three-vortex pairing are shown through employing a passive conserved scalar method. The simulations lead to that the relative phase of subharmonic mode is one of the important fac- tors related to the different nonlineax evolutions of the primary vortices, and that it can directly impact the disturbance energy, shear layer thickness, and mixing efficiency. Especially, in the vortex-tearing case, the energy of subharmonic mode is reduced eventually, so it influences weakly the energy of primary wave and the shear layer ibidness. Calculation results are similar to the existed experiment images, which indicate that there is an inherent relation between the unstable linear waves and the real vortex interaction types in compressible shear layers. Furthermore, the numerical method used here is good for study of the multi-scale complicated flows.更多还原