基于大涡模拟的圆柱绕流剪切层不稳定性

Shear Layer Instability of Flow Around a Circular Cylinder Based on Large Eddy Simulation

圆柱绕流是一种常见的流体力学研究对象,随着雷诺数(Re)增加,其下游尾迹剪切层中会产生开尔文-亥姆霍兹不稳定性现象.利用大涡模拟方法,数值求解中等Re(Re=2000,3900,5000)的圆柱绕流问题,可得圆柱下游的精细化流场,继而开展对剪切层不稳定性的深入研究.为获得剪切层不稳定性的特征频率,分别采用传统的监测点分析与局部流场的动态模态分解方法进行计算.结果显示,两种方法得到的频率基本一致.不过,相比传统方法,动态模态分解方法一方面能克服人为选择监测点带来的随机误差,较便捷地给出剪切层不稳定性特征频率,另一方面还能进一步通过不同流场模态分析出不同Re对剪切层不稳定性特性的影响.

The flow around a cylinder is a common research object of fluid mechanics.As the Reynolds number(Re)increases,the Kelvin-Helmholtz instability of the shear layer will occur in the wake behind the cylinder.Using the large eddy simulation method to investigate the problem numerically in a medium range of Re(Re=2000,3900,5000),the refined flow field behind the cylinder can be obtained,and an in-depth study of the instability of the shear layer can be conducted.To get the characteristic frequency of the shear layer instability,two methods,i.e.,the traditional analysis of monitoring points and the dynamic mode decomposition method on the local flow field,are used.The results show that the frequencies obtained by the two methods are basically the same.However,compared with the traditional method,the dynamic mode decomposition method can overcome the random error caused by the artificial selection of monitoring points,and can give the characteristic frequency of shear layer instability more conveniently.In addition,it can further analyze the influence of different Re values on the instability characteristics of the shear layer based on different flow field modes.