Control of flow past a dimpled circular cylinder

In this paper, the flow past a circular cylinder with dimpled surface (the roughness coefficient k/D = 0.05, k is the depth of the dimple hole, and D is the diameter of the cylinder) was investigated. The experiments were conducted in an open water channel and the Reynolds number ranged from 7.43 × 103 to 1.798 × 104. Drag and lift forces on the cylinder were measured directly using a load cell. Two types of surface roughness were investigated, i.e., half dimpled and fully dimpled. The study revealed that the cylinder covered with dimples uniformly over the total surface could produce a drag coefficient of about 90% of a smooth cylinder. On the other hand, the force coefficients (drag and lift) of the half dimpled cylinder varied considerably, depending on the orientation of the dimpled surface with respect to the incident flow. The flow field in the wake of the cylinder was measured using particle image velocimetry (PIV) technique, confirming that the dimpled surface could affect the strength of vortex shedding from the cylinder.