Active Harmonic Destalization of Coherent Vortex Flows

本文的目的是研究在许多实际流动中发生的相干涡结构的不稳定和解体的物理机制，例如在运动物体的附属物连接处形成的马蹄形涡，以及湍流剪切层中的相干顺流涡。这些流动中的涡旋代表了能量的大量消耗，并且对施加在相关物体或系统上的流体力有相当大的影响；旋涡会引起结构振动，产生流动噪音，产生过多的流动阻力，在大型飞机降落时，旋涡对会对其他从繁忙机场起飞的飞机造成重大危害。这些流动的一个共同特征是，涡旋要么以施加的弱应变形式存在，要么以剪切形式存在，其影响之一是扭曲涡旋核心结构的形状。现有的实验或数值模拟结果表明，在这些流动上施加一定频率的外部周期压力场或流动扰动对相干涡有显著的影响，在某些情况下引起相干涡的抑制。

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.