VELOCITY MEASUREMENTS ON FLOW AROUND A CYLINDER

Abstract

If the cylinder is set in an open channel, the flow upstream will undergo a separation of the turbulent boundary layer and rolls up to form the well-known horseshoe-vortex system, which is swept around the cylinder. The flow fields around a cylinder positioned normal to the flow in an open channel have been investigated experimentally for two types of flow. An Acoustic Doppler Velocity Profiler was used to obtain instantaneously the three directions of the velocity in the flow. Results of the experiments present the vertical velocities distributions of the flow around a cylinder, showing a highly three-dimensional picture, being reasonably organized in the front and less organized in the back of the cylinder, where flow separation takes place. It also shows that a horseshoe-vortex system is established, existing of a measurable vortex with underneath a return flow. The system develops itself in the upstream corner at the nose of the cylinder and stretches around towards the downstream.