Visual observations of the flow around a half-submerged oscillating sphere

Visual observations are made on the flow around a sphere which is half-submerged in still water and forced to oscillate up and down. It is found that three kinds of steady flows are generated in the water: the surface flow, the undersurface flow, and the vertical jet flow. The surface flow is produced in the very thin layer on the water surface. The undersurface flow is induced in the thick layer under the water surface. The vertical jet flow is ejected vertically from the bottom of the sphere. The surface flow and the undersurface flow are produced only when petal-shaped waves are generated on the water surface. The velocity of the undersurface flow is much smaller than that of the surface flow.