Formation and evolution of the streamwise vortices in mixing layers

The evolution of the three-dimensional time-developing mixing layer is simulated numerically using the pseudo-spectral method. The initial perturbations used in this study consisted of the two-dimensional fundamental wave and the streamwise-invariant three-dimensional disturbance. A comparison of the formations of the streamwise vortices with different amplitude functions for three-dimensional disturbances is made. In one case the results are similar to that of Rogers & Moser^[1], whereas a different way in which the quadrupole forms and sudden expansion of the rib are observed in another case. The simulation also confirms that the stretching by the forming roller rather than Rayleigh centrifugal instability is responsible for the formation of the rib. Finally, numerical flow visualization results are presented. The project supported by the Zhejiang Province Natural Science Special Fund for Youth Scientistis' Cultivation.     

Nonlinear Group Interactions of the Taylor–Görtler Disturbances in Supersonic Axisymmetric Jets

The nonlinear group interaction of the Taylor-Görtler disturbances (streamwise vortices) at the initial section of a supersonic axisymmetric jet is numerically studied within the framework of the weakly nonlinear theory of stability. The experimentally observed spectrum of disturbances is considered. The regular and specific features of the streamwise dynamics of various wave components for a turbulent jet are studied. It is shown that such an interaction in the coupled mode in resonant group triplets allows one to describe the experimentally observed elevated growth of background components of the real spectrum.     

CFG桩复合地基沉降影响因素分析

对绕2D水翼无分离流边界层内的初生空化形态进行了实验研究. 采用高速摄像机观测 了空化初生结构的形态，应用2D-LDV测量了空化初生时翼型周围的流动速度分布，并对实 验结果进行了分析. 结果表明：绕水翼无分离边界层内，初生空化结构中空泡伴随 着近壁湍流拟序结构的发生而出现，在初生空化条件下，形成空化涡结构，大量的微空泡产生于发夹 涡结构中，并在涡结构的猝发过程中出现生成---长大---溃灭---反弹---再溃灭的过程. 初生空 化涡结构具有空泡和近壁拟序结构双重特性.