Numerical Study of Dimple Effect on a Golf Ball
Under conventional perception, a smooth ball is always expected to have a smaller friction force than a dimpled ball, hence, a smooth ball is expected to fly further. Jearl  showed that the phenomenon is exactly the opposite, a dimpled ball flies four times further than a smooth ball. Jorgensen  noted that concaved surface of dimples generates small-scale turbulence and leads to drag reduction. Choi et al  proposed that the drag reduction mechanism is related to the development of a shear layer instability that leads to higher momentum near the wall, causing local flow reattachment and a delay in complete flow separation. This reduces the low pressure region trailing the golf ball and therefore lowers the air drag. We have numerically studied this phenomenon. In this study under-resolved Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES), and Delayed-Detached Eddy Simulation (DDES) were used for the smooth and dimpled balls, respectively. Drag, lift and pressure coefficients, and separations angles for smooth and dimpled balls were obtained by the simulations. We have shown that dimples on a ball surface significantly decreases the drag by delaying the complete flow de-attachment. Additionally, a dimpled ball was shown to experience a smoother flight than a smooth ball by the study of vortex shedding frequency.
 Jearl, W., “More on boomerangs, including their connection with the dimpled golf ball” Scientific American, pp. 180, 1979.
 Jorgensen, T. P., “The Physics of Golf, 2nd edition,” New York: Springer-Verlag, pp. 71-72, 1999.
 D. Kim and H. Choi, ‘‘Large eddy simulation of turbulent flow over a sphere using an immersed boundary method’’ Third AFSOR International Conference on Direct Numerical Simulations and Large Eddy Simulations (University of Texas, Arlington, Texas, 2001).
Gépészmérnöki alapszak (BSc)
Dr. Davidson Josh
Research Fellow, Áramlástan Tanszék