Abstract:

The flow characteristics of the sphere under uniform flow in a large space have been extensively studied, but the influence of the wall on the flow characteristics of the sphere is not clear. The wake of the particle is focused. Results show that there are three regimes of the sphere wake, which are steady wake, unsteady symmetric wake and unsteady asymmetric wake. If Re<150, steady wake occurs, and the wake is symmetric with respect to a plane perpendicular to the wall. If 150<Re<400, the wake is still planar symmetric. When the Reynolds number is large, regular and periodic vortex shedding occurs behind the sphere, and the Strouhal number is about 0.26－0.33. The vortex is planar symmetric with respect to a vertical plane passing through the sphere center and the vortex. The frequency band of the power spectra of the sphere wake is wide. If Re>400, the vortex shedding is not symmetric and becomes chaotic as Reynolds number increases.

Key words: stationary sphere near a wall, wake, vortex shedding, symmetry breaking, power spectra

摘要：

圆球在大空间均匀来流下的绕流特性已得到了广泛的研究，但是壁面对圆球绕流特性的影响还未清楚。通过实验方法研究了与壁面接触的静止圆球在明渠流中的绕流特性，重点关注了圆球后尾迹的特性。研究发现，圆球尾迹存在三种状态：稳定状态、非稳定对称状态和非稳定非对称状态。当Re<150时，尾迹呈稳定状态，尾迹关于垂直于壁面的平面对称；当150<Re<400时，尾迹呈对称状态，Reynolds数较高时，圆球后存在规则的、周期性的涡脱落，Strouhal 数为0.26~0.33，脱落涡关于垂直于壁面的平面对称，此时尾迹功率谱的频带分布较宽；而当Re>400时，圆球后的涡脱落不再对称，尾迹随着Reynolds数的增大呈现混沌特征。

关键词: 近壁面静止圆球, 尾迹, 涡脱落, 对称性破缺, 功率谱