Velocity measurements of vortex structures induced by sphere/wall interaction

This study experimentally investigates the vortex structure induced by sphere-wall collision and a falling sphere in a viscous liquid. The velocity fields of sphere-induced vortices were measured with refractive-index-matched materials and particle tracking velocimetry. The Reynolds number, based on the sphere diameter and the falling velocity, was in the range of 350–3200. The results revealed that the sphere-induced vortex ring was axisymmetric when the Reynolds number Re is ≤ 800. For the case of Re = 2000, the vortex structure developed into a non-symmetric flow after the sphere collided on the wall. Nonetheless, the influence of the Reynolds number on the vortex trajectory is insignificant. The moving speed of the primary vortex increases as the Reynolds number increases. In addition, the trajectories of free-falling spheres at a high Reynolds number of Re = 3200 deviate from a vertical straight line, owing to the non-axisymmetric flow field around the sphere. The experimental results presented in this work can be used to validate numerical schemes for solid/vortex interaction problems.