Abstract
The velocity field of the flow around a circular cylinder started impulsively from rest was studied by the aluminium dust method. The experiments were carried out at Re=1, 200 and when τ=U0t/d was from 0 to 5, where Re is the Reynolds number based on the diameter d of the cylinder, U0 the cylinder speed, and t the time after the start of the cylinder. Circulations taken along several closed contours around a vortex-center, and the positions of vortex-center were measured during the motion of the cylinder. On the basis of these measured values, the velocity fields in the vortex region were calculated by using a simple model which approximates the vortex flow by a single viscous point-vortex. The analytical results were in a fairly good agreement with the experimental results.
