A diagnostic experimental technique for studying coherent structures in plane turbulent wakes

Abstract

The far region of a plane turbulent porous-body wake is examined by means of velocity measurements in a wind tunnel with a uniform distortion section. The latter is shown to be a useful diagnostic tool for determining details of the coherent structures in the wake. Rapid distortion theory, used in conjunction with kinematically modelled coherent structures, provides insight into the effect of the distortion, as well as aiding in and verifying the interpretation of results obtained via a pattern-recognition technique. These results serve to indicate that horseshoe vortices with spanwise periodicity are present in the far wake. These coherent structures, when uniformly distorted, become elongated and more two-dimensional, because of their increased spanwise vorticity and decreased lateral vorticity.