Aerodynamic flight analysis of tennis ball and fluid analysis by PIV

Abstract

For amateur tennis players, tennis balls are not consumable but durable items. Therefore, it is important to grasp the changes in flight characteristics between new and worn balls. Aerodynamic characteristics were measured in wind tunnel experiments with new balls and worn balls on two official balls that are mainly used in Japanese amateur tennis. Aerodynamic measurements were performed by the performance of the averaged amateur players targeted in this study. The coefficient of drag, C_D, was obtained from 0.7 to 0.9, but some did not change due to wear. The coefficient of lift, C_L varied from 0.05 to 0.3 and increased in proportion to the spin parameter, S_p. The flow around the spinning ball was also visualized by PIV measurements to understand the effect on aerodynamic performance. A correlation was found between the drag coefficient and the range of wake by PIV analysis. Regarding C_L, there was no difference in the value of C_L and the streamline direction between the new and worn balls. Still, the vortex generated behind the ball was different, and streamlines confirmed the difference in C_D. Also, simulation of flight trajectory prediction was performed using the fluid force measurement results by the wind tunnel experiments. Although there was almost no difference in the flight trajectory of the new balls, the flight trajectory of the worn shots was different due to the change in aerodynamic characteristics caused by the difference in felt deterioration. The flight performance due to the deterioration of the ball was confirmed, and it was found that the difference varies depending on the ball manufacturer.