Flow similitude and vortex lock-on in bluff body near wakes

Abstract

Some years ago a universal Strouhal number for bluff body wakes was introduced, which was based upon the Strouhal frequency fs0 of the vortex shedding, 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 on the body. This universal parameter was shown to collapse these characteristic scales of bluff body flows onto a single curve for wake Reynolds numbers between 200 and 107. The results of more recent experiments show the concept of universal wake similitude to be even more general than was previously supposed. In this paper these similarity relationships are applied to the case of vortex lock-on in oscillatory flow. A full understanding of the macroscopic averaged properties in the wake in this traditional manner is an important precursor to studying, in detail, the microscale wake properties using the most modern experimental measurements and diagnostic techniques and theoretical concepts such as the absolute-convective stability of shear flows.