Aerodynamic forces on projectiles used in various sports

The aerodynamics of projectiles used in various sports is investigated via experiments in a low speed wind tunnel. Force measurements are carried out on actual artifacts at speeds in the range of 15-75 m/s. The sports considered include golf, field hockey, soccer, baseball, tennis, cricket, volleyball, and badminton. Both synthetic and duck-feather models of shuttle-cocks used in badminton are considered. The variation of the coefficient of drag, C_D, with Reynolds number, Re, is quite different for the two models. The deformation of the synthetic model increases significantly with an increase in speed, leading to a decrease in C_D with an increase in Re. The duck-feather model, on the other hand, does not undergo such severe deformations. Force measurements for a baseball are carried out for three different orientations of its seam with the free-stream flow. Variation of C_D with Re for two internationally approved brands of golf balls is presented for the first time in the open literature. The data are compared with those for a ball used in field hockey, which also has dimples on its surface, albeit of different sizes and distributions. Force measurements are carried out on a new cricket ball as well as one whose surface is manually roughened to resemble a ball that has been in play for about 40 overs (=240 deliveries). The study brings out the regimes of conventional- and reverse-swing and their dependence on the surface roughness of the ball. Experiments on balls with differential roughness of the two hemispheres of the ball are utilized to study the “contrast-swing.” Particle Image Velocimetry measurements are carried out for the 3D-printed model of a new cricket ball to explore the phenomena of conventional- and reverse-swing. Experiments on a tennis ball bring out the role of the fuzz in the transition of the boundary layer on its surface; a near-constant C_D for the entire range of Re that is studied is observed. The brands of a soccer ball and volleyball that are tested exhibit very similar behaviour. In the supercritical regime, an increase in C_D is followed by its decrease with an increase in Re.