UNSTEADY FLOW PAST A CIRCULAR CYLINDER

The symmetrical unsteady vortices behind a circular cylinder started from rest either impulsively of with uniform acceleration were investigated experimentally using a flow visualization technique. The variation of the length of the vortices with time was determined from the photographs obtained at Reynolds numbers ranging from 31 to 1700 and dimensionless accelerations from 195 to 2.44×105. The length of the unsteady vortices exceeds 4.3 cylinder diameters at about a Reynolds number of 100, or a dimensionless acceleration of 500. The secondary vortices were formed upstream side of the main vortices at Reynolds numbers higher than 550, or dimensionless accelerations higher than 5×105. © 1969, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.