Drag measurements of a circular cylinder with moving surface boundary-layer control

Abstract

Experimental results of flow around a circular cylinder with moving surface boundary-layer control (MSBC) are presented. Two small rotating cylinders strategically located inject momentum in the boundary layer of the cylinder, which delays the separation of the boundary layer. As a consequence, the wake becomes narrower and the fluctuating transverse velocity is reduced, resulting in a recirculation free region that prevents the vortex formation. The control parameter is the ratio between the tangential velocity of the moving surface and the flow velocity (Omega = Uc/U). The main advantage of the MSBC is the possibility of combining the suppression of vortexinduced vibration (VIV) and drag reduction. The experimental tests are preformed at a circulating water channel facility. In order to verify the effectiveness of the MSBC regarding drag reduction, two different techniques were employed to measure the mean drag of the cylinder with and without MSBC. The first method used a load cell to measure the drag, while the second one was based on the integration of velocity data along a line located on a averaged velocity field obtained through particle image velocimetry (PIV).