THE INITIAL FLOW PAST AN IMPULSIVELY STARTED CIRCULAR CYLINDER

Abstract

The initial flow in a direction normal to an infinite circular cylinder which is started impulsively from rest with uniform velocity in a viscous fluid is considered. An expansion in powers of the time from the start of the motion is obtained which extends the results of boundary-layer theory by taking into account corrections for finite Reynolds numbers. The odevelopment of the physical properties of the flow at early times for finite Reynolds numbers may thus be obtained. In particular, a reasonably good approximation to the time at which the fluid first starts to separate from the cylinder can be calculated down to about R = 200, where R is the Reynolds number based on the diameter of the cylinder. The expansion is valid for times beyond the time at which separation first occurs, if R is large enough. Results are presented for the initial development with time of the drag on the cylinder. At the start of the motion the friction and pressure drags are equal for all Reynolds numbers.