Effect of an Oscillating Free Stream on the Unsteady Pressure on a Circular Cylinder

Abstract : An experimental investigation was made of the unsteady pressure on a circular cylinder in a free stream of constant and oscillating velocity. Consideration of possible resonant coupling mechanisms between the Karman vortex street fluctuations and freestream velocity oscillations showed such coupling to be insignificant, if any. It appears that the independence of symmetric and antisymmetric modes in linear systems brings about this fortunate circumstance in these nonlinear flows. Designs involving bluff bodies in flows with pulsations should therefore be much safer than previously believed. In such flows the Strouhal number evidently scales with the 'instantaneous' velocity when the pulsations are slow and with the mean velocity when the pulsating frequency is of the same order as the frequency of the vortex street. (Author)