Velocity Field of the Flow Around a Circular Cylinder Started Impulsively : 2nd Report, Unsteady Boundary Layers

Abstract

A procedure for obtaining true velocities which were estimated from the locations of time-lines visualized by hydrogen bubble technique was developed by taking into account the velocity defect behind a bubble generating wire. By using this technique, the velocity profiles in unsteady boundary layer on the circular cylinder which was started impulsively in still water were obtained at the Reynolds number of 1200 based on the cylinder diameter. changes in the displacement thicknesses and shape factors were determined in course of time and were discussed in comparison with the results by the existing theories. Velocity profiles of the boundary layer before and after the occurrence of a reversed flow were also measured. These velocity profiles were in fairly good agreement with Pohlhausen's profile, even at the location where a reversed flow appears. And they seem to change gradually before and after the occurrence of a reversed flow, unlike the velocity profiles at separation points in ordinary steady flows.