Effect of surface design on drag properties of soccer balls

The paper describes the critical Reynolds number of soccer balls as a function of the total groove volume on the ball surface. In this study, the aerodynamic drag and separation point of 6 soccer balls with different panel orientations were measured in a wind tunnel. Moreover, the total volume of grooves on the ball’s surface was measured by One shot 3D measuring machine. It was found that the drag coefficient in the supercritical region and the critical Reynolds number depend on the design of the ball surface (shape, number of panels, surface roughness). A negative correlation exists between the total groove volume on the surface and the critical Reynolds number. When the total groove volume is large, the drag in the supercritical region increases. The position of the separation point does not change in the subcritical and supercritical regions even if the orientation of the panel is changed. However, when the groove width is wider, the panel orientation dependence becomes significant in the supercritical region. In the transition region, the position of the separation point differs depending on the panel's orientation.