关键词: 流动控制, 电磁力控制, 圆球绕流, 壁面效应, 尾涡结构

Abstract:

With the near-wall effect， the variations of the flow field structure of flow around a sphere at a Reynolds number of Re=300 with wall distance are numerically investigated. The electro-magnetic force control coupled with the near-wall effect is further studied and discussed. The results demonstrate that when the sphere is far from the wall （gap ratio G/D≥6）， the near-wall effect can be neglected on the wake structures of the sphere. As the gap ratio G/D decreases， the near-wall effect is gradually enhanced， the hairpin vortex structures in the wake of the sphere rotate 180° clockwise as a whole， the vortex legs are gradually thinned， and then turn into a double-line vortex structure. The lift force gradually decreases from a positive value to zero and then to a negative value. The direction of the lift force is gradually changed from pointing away from the wall to pointing toward the wall. In addition， for the case where the sphere is at a gap ratio G/D=1.4， electro-magnetic force control in different directions is performed. With the application of a positive electro-magnetic force， the wall effect blocks the acceleration effect of the flow field by the electro-magnetic force. This leads to the pressure on the lower side of the sphere larger than that on the upper side， thereby directing the lift force away from the wall. With the application of a negative electro-magnetic force， the wall effect blocks the deceleration effect of the flow field by the electro-magnetic force. This leads to the pressure on the lower side of the sphere smaller than that on the upper side， thereby directing the lift force toward the wall.

Key words: flow control, electro-magnetic force control, flow past a sphere, wall effect, wake vortex structures