Experimental investigation of lift and drag on a ball rotated by an inclined water jet

Abstract

The lift and drag of rotating balls with Reynolds numbers from 4500 to 6500 were obtained using a ping‐pong ball impinged by a water jet with inclination angles ranging from θ = 3.43° to 11.3°. Results show that water strikes the ball surface and leaves from the wake region behind the ball, which spins more slowly when a large amount of water stays on the ball surface, causing low lift and low drag forces to be exerted on the ball. In contrast, the ball spins quickly when a small amount of water stays on the ball surface. This causes high lift force to be exerted on the ball, which verifies the Magnus effect of a rotating ball. The drag force increases nonlinearly with the angular speed of the ball because there is a branch flow out from the stretched wake behind the ball. Results also indicate that the lift force of the ball increases with jet exit speed, but the drag force does not change significantly with the jet exit speed. This reveals that the momentum change in the direction parallel to gravity is more significant than that in the direction normal to gravity.