基于LES的圆柱尾流漩涡特性分析

Analysis of vortex characteristics in wake of circular cylinder based on LES

为研究大涡模拟（LES）方法在圆柱绕流和模拟大尺度和小尺度波动的适用性,采用Smagorinsky-Lilly模型对亚临界区7种雷诺数（Re）情况的圆柱绕流进行数值模拟,计算出其阻力系数（Cd）和Strouhal数（St）,并针对Re=3 900情况进行深入分析,给出其漩涡脱落的过程和速度的功率谱曲线.研究结果表明：计算所得Cd和St均与以往实验值符合较好,能较好模拟圆柱绕流尾涡周期性脱落过程;采用LES方法不仅能精准地捕捉到圆柱绕流漩涡脱落的无量纲频率0.215,而且能有效反映出圆柱下游回流区长度在大时间尺度上的周期性变化所对应的频率0.006 15,这与实验值和直接模拟（DNS）所得频率相符合;对于小尺度的Kelvin-Helmholtz不稳定性,虽能捕捉到波动,其频率为0.641,但与直接模拟结果和实验所得公式的预测结果有一定的差值.

To investigate the capability of large-eddy simulation（LES） method for simulating the flow around a circular cylinder and the large-and small-scale fluctuation,Smagorinsky-Lilly model was adopted for numerical simulation under the seven sub-critical Reynolds number（Re） circumstances to obtain the drag coefficient（Cd） and the Strouhal number（St）.The vortex shedding process and the velocity’s power spectrum curves were given for several probes located in the near wake,at Re=3 900.Research results show that the calculated Cd and St values are well in tune with the previous experimental data,which could well simulate the periodic shedding process of the flow around circular cylinder.The LES method can not only capture the eddy shedding non-dimensional frequency of 0.215,but effectively reflect the frequency of 0.006 15,related with the large-scale almost periodic change of the length of recirculating zone,which are in good according with the experiment and direct numerical simulation（DNS） results.For the small-scale Kelvin-Helmholtz instabilities,although it can be captured with frequency at 0.641,however,there is still difference from the expected value according to the DNS results and formulas of the experiment.