Active Harmonic Destalization of Coherent Vortex Flows

本文的目的是研究在许多实际流动中出现的相干涡结构失稳和解体的物理机制，例如在运动物体上的附件交界处形成的马蹄涡，以及湍流剪切层中的相干流向涡。这些流动中的涡流代表着能量的显著消耗，并对施加在相关物体或系统上的流体力有相当大的影响；涡流引起结构振动，导致流动噪声，产生过大的流动阻力，对于大型飞机的情况，涡流对从繁忙的机场起飞的其他飞机构成重大危险。这些流动的一个共同特征是，涡旋持续存在于施加的弱应变或剪切中，其影响之一是扭曲了涡核结构的形状。已有的实验或数值模拟结果表明，在某些情况下，施加一定频率的外部周期压力场或流动扰动，会对相干涡旋产生显著的影响，导致相干涡旋的抑制。

The object of this review is to investigate a physical mechanism for destabilization and disintegration of structure of coherent vortices which occur in many practical flows such as the horseshoe vortices which form at the junction of an appendage on a body in motion, and the coherent streamwise vortices in a turbulent shear layer. The vortices in these flows represent a significant drain in energy and have considerable bearing on the fluid forces exerted on the associated body or system; the vortices induce structural vibrations, contribute to flow noise, generate excess flow drag and in the case of the vortex pair in the wake of a large aircraft present significant hazard during landing to other aircrafts taking off from busy airports. A common feature of these flows is that the vortices persist either in an imposed weak strain or shear, one of the effects of which is to distort the shape of the core structure of the vortices. Available experimental or numerically simulated results suggest that imposing an external periodic pressure field or flow perturbation at certain frequencies on these flows has dramatic effects on the coherent vortices, inducing their suppression in some cases.