自由端狭缝吸气控制三维方柱绕流

Flow control around a three dimensional square cylinder with free-end slot suction

利用大涡模拟(LES)方法研究了顶部定常狭缝吸气对正方形截面有限长柱体的气动力与绕流特性的影响规律。对比了吸气系数Q=0、1、3时的气动力特性及绕流情况,尤其是自由端附近的流动结构。Q=U/U∞,其中U为吸气狭缝入口风速,U∞为自由来流速度。研究发现,顶部定常吸气可以有效地抑制三维柱体气动力,且Q=1时抑制效果最为显著,相对于无控制工况,时均阻力C D、脉动阻力C′D和脉动升力C′L分别减少了3.92%、19.08%和40.88%。在Q=1时,柱体自由端负压和压力脉动最为显著,有利于柱体两侧形成上升流;顶面压力脉动最强有利于自由端剪切流与尾流间的动量交换,可以有效地抑制柱体展向涡脱落,减小柱体气动力;同时柱体顶面流动出现再附分离现象;而在Q=3时柱体顶面大部分区域流动分离被完全抑制。

Large eddy simulation(LES)is used to study the influence of free-end steady slot suction on the aerodynamic forces and flow around a three dimensional finite-length square cylinder with a square cross-section.The aerodynamic forces and the flow around the cylinder have been compared systematically for the suction ratios Q=0,1 and 3.Special attention is paid on the flow around the free end of the cylinder.It is found that free-end steady slot suction can effectively suppress the aerodynamic forces of the model.The Controlling result is the best when Q=1.Relative to the none control case,the mean drag,fluctuating drag,and fluctuating lift are decreased by 3.92%,19.08%,and 40.88%,respectively.The mean negative pressure and fluctuating pressure on the free end are most significant at Q=1,which enhances the upwash flow along cylinder side faces and the momentum exchange between free-end shear flow and near wake flow.Thus,this behavior effectively suppresses the spanwise vortex shedding and the aerodynamic forces of the cylinder;at the same time,the flow separation and reattachment occurred on the top of the cylinder.When Q=3,the flow separation in most areas of the top surface of the cylinder is completely inhibited.