Numerical investigation of the flow over a golf ball in the subcritical and supercritical regimes

Direct numerical simulation (DNS) is applied within the framework of an immersed boundary approach to understand the role of surface dimpling on the flow over a golf ball. In the present study, DNS results are reported for simulations in the subcritical (Re = 2.5x10⁴) and supercritical regimes (Re = 1.1x10⁵) using as many as 1.2x10⁹ grid points. Flow visualizations reveal the differences in separation characteristics between the two Reynolds numbers. Profiles of the mean velocity indicate that the flow detaches completely at approximately 90 degrees in the subcritical case (measured from the stagnation point at the front of the ball), while in the supercritical regime there are alternating regions of reattachment and separation within dimples with complete detachment around 110 degrees. Energy spectra highlight frequencies associated with vortex formation over the dimples prior to complete detachment in the supercritical regime. Reynolds stresses quantify momentum transport in the near-wall region, showing that the radial and axial stresses increase around 90 degrees for the subcritical case. In the supercritical regime these stress components alternately increase and decrease, corresponding to local separation and reattachment. Prediction of the drag coefficient for both Reynolds numbers is in reasonable agreement with measurements.