Effect of free stream turbulence on the flow around bluff bodies

Abstract

Many bodies of practical interest are bluff, and there is a large volume of literature which deals with various aspects of the very complex flows about them. Most of the work done to data has been experimental, with the majority of it in wind tunnels in flows with low levels of free stream turbulence (FST). By contrast, in actual applications one often encounters fluid streams with high levels of FST. This introduces an additional parameter into an already complex problem, one which has to be understood before wind tunnel data may be properly extrapolated and applied. In this review the basic mechanisms by which FST and the overall mean flow over bluff bodies (at high Reynolds numbers) interact are discussed in some detail. There are three basic mechanisms that may be identified: accelerated transition to turbulence in shear layers, enhanced mixing and entrainment, and distortion of FST itself by the mean flow. The overall effect of FST is often the result of more than one of these basic mechanisms. The nature of the effect, and its magnitude, are illustrated by examples which show that in some cases it depends on both the intensity and the scale of the FST, while in others only intensity is important.