Effect of Surface Texture on the Lift and Drag of Small Spinning Balls

Spherical balls of various sizes and weights are frequently used in numerous disciplines and in recreational events, whereby spinning the ball, its trajectory can be modified. The shape of the curved path depends on a variety of factors such as the spin rate and orientation, the ball’s speed, its weight, the surface texture, and even weather conditions. The effect of rotation, often called the ‘Magnus effect’, is named after the German physicist who in the mid 1800s studied the effect of spin on the trajectory of artillery projectiles. In the published literature, under certain condition, the direction of the ‘classical’ Magnus effect was found to be reversed. Therefore, the focus of the current study was on searching ways to change or even reverse the direction of the aerodynamic lift in small spheres (by modifying the surface roughness). Consequently, standard ping-pong balls were used to represent a ball with smooth surface, and golf balls were used to demonstrate the effect of rough surface texture. Both wind tunnel and computational tools were used for this study, the first mainly to measure the aerodynamic forces. The computational tools were used to calculate the flow over these spherical shapes, providing complementary information for the wind tunnel tests such as surrounding streamlines, surface pressures, separation lines, and surface friction. The experimental results indicate that minor changes in the ping-pong ball’s surface roughness can reverse the ‘Magnus effect’.