Universal Similarity in the Wakes of Stationary and Vibrating Bluff Structures

Abstract

A universal wake Strouhal number, St* =fsd′/Ub, has been proposed and is based upon the Strouhal frequency fs of the incident flow, the measured wake width d′ at the end of the vortex formation region, and the mean velocity Ub at the edge of the separated boundary layer. This universal parameter collapses these characteristic parameters for bluff bodies onto a single curve for wake Reynolds numbers between Re* = 100 and 107. The pressure drag, vortex shedding frequency and base pressure are related through an inverse dependence between St* and a wake drag coefficient CD* = CD/(d′/d) K2, where K = (1−Cpb)1/2. The product St* CD* is equal to a constant value of 0.073 ± 0.005 for Re* in this same range of Reynolds numbers.