圆柱绕流远场涡对的数值模拟

Numerical simulation of the vortex couples in the far wakes of behind circular cylinder

基于离散涡方法求得非定常、不稳定流场,数值模拟了三种不同时刻高雷诺数下圆柱绕流涡结构的发展. 从流谱图、等涡量线图和涡谱图可以清晰地看出从近场的初生卡门涡街,过渡到远场的二次涡街的过程. 计算结果发现: 远场离散涡有形成二个涡的涡对及三个涡的涡对的趋势. 计算结果说明了流体运动中涡对结构的本质: 由于来流是均匀的,没有加入任何扰动,当流体流过钝体时产生具有剧烈分离的不稳定流动,因此在远场形成的二次涡对及卡门涡街是由于流体本身的动力不稳定而引起的. 从而增加对远场尾迹流及涡对结构的理解.

The present research on the structure of vortex couples in the far wakes of circular cylinder was carried out numerically. The unsteady and unstable flow field is evaluated with the discrete vortex method. Based on the obtained flow field, the pattern of vortices and the contours of vorticity are then solved simultaneously. The transition process from the primary Karman vortex street to the secondary vortex street is clearly distinguished by the numerical results. The discrete vortices in the far wakes have the trend of becoming to be the couples of two and three vortices. The numerical results tell the essence of the vortex structure in the flow field. The formation of the secondary vortex couples and the Karman street is arosen due to the dynamic instability of the fluid itself, because the primary incoming flow field is homogenous and undisturbed. Each of the couple of two vortices has equal vorticity, but their directions of vorticity are reversed. In the couple of three vortices, one has the same amount of vorticity of the other two vortices, but their directions are different too. The unstable flow is produced in the process of flow separated from the blunt body. From the results, the far wakes and the structure of vortex couples can be understood clearly.