The wakes of cylindrical bluff bodies at low Reynolds number

Abstract
The wakes of bluff bodies have been investigated by means of flow visualization, with dye washed from the rear of the cylinders, at Reynolds numbers less than 2000. Observations were made in a towing tank which, for most of the measurements, had been treated to produce minimal background motions. The majority of the work concerns the flow past circular cylinders, but some measurements have been made on cylinders of square and diamond section as well as on a flat plate towed broadside on. The effect of splitter plates in the wakes of circular cylinders has also been investigated. The principal investigations have been concerned with the separation bubble behind bodies at very low Reynolds number; the Reynolds number (Re$_{\text{osc}}$) above which oscillations are always found; the wake frequency; the mode of formation and the motion of the wake vortices; the transition to turbulence and with details of the flow in certain ranges of Reynolds number. The range is divided into the following regimes: Re < Re$_{\text{osc}}$ Steady flow; standing eddies. Re$_{\text{osc}}$ < Re < Re$_{\text{vs}}$ Wavy wake, no accumulation of dye into vortices. Re$_{\text{vs}}$ < Re < 100 Vortex street wake; remnants of the standing eddies still present; diffusion of vorticity important. 100 < Re < 140 Increased efficiency of convective mass transfer behind the body; an accelerating phase of vortex motion present up to Re = 500. 140 < Re < 500 Fingers of dye moving back towards the body from the wake; vortex strength irregular; more nearly two-dimensional flow; transition to turbulent vortex cores downstream. 250 < Re < 400 Transition to high Re type of vortex shedding. 350 < Re < 2000 + Transition waves in the separated layers and transition to turbulence in the vortex cores on formation.

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