VORTEX FLOW VISUALIZATIONS INSIDE AND AFTER THE SURFACE DIMPLES OF DIFFERENT SHAPE AND CONFIGURATION

INTRODUCTION Over the last twenty years the intensive research effort was focused on studies of hydrodynamics and heat transfer over surfaces with indentations (dimples). The early discoveries of low drag penalties for golf balls were made in [1] demonstrating the effectiveness of the shallow surface dimples to cause the pressure losses and early boundary layer transition without the drag penalties associated with sand roughness. Unlike round balls with either smooth or sand roughened surfaces, the dimpled ball drag curve remains almost constant at the supercritical Reynolds numbers (Fig.1). Due to reductions in the backside separation zone the drag coefficient of a dimpled ball at Re<60,000 is substantially lower than that over a sanded or smooth ball. These results indicate the dimples have a more beneficial effect on the drag reduction and laminar-turbulent transition than sand roughness.