VELOCITY FIELD OF THE FLOW AROUND A CIRCULAR CYLINDER STARTED IMPULSIVELY - 1. OUTER POTENTIAL FLOW.

The flow around a circular cylinder started impulsively in water at rest was studied by the hydrogen bubble technique for the Reynolds number of 1200 based on the diameter of the cylinder. Taking into account the velocity defect behind the bubble generating wire, a method of calibration for quantitative determination of the flow velocity was established. In order to see the influence of the growth of separation vortices formed behind the cylinder on the potential flow field, the velocity field near the cylinder surface and the vorticity flux shedding from the boundary layer through the separation points were measured in relation to the time elapsed. The potential flow around the cylinder was found to change markedly with the time in which the growth of vortices in the wake was promoted.