Vortex Dynamics in the Wake of a Cylinder

Abstract

Two-dimensional and three-dimensional vortical instabilities in wakes have been a subject of interest to engineers and scientists for a great many years. Although the problem of an unseparated wake behind a splitter plate or symmetric airfoil is amenable to analytical studies, for example stability analysis, the wake of a nominally two-dimensional (2-D) or three-dimensional (3-D) bluff body poses rather a greater analytical challenge. Approaches to this problem have been principally experimental, although there has recently been a surge of activity in numerical simulation and analysis. Bluff body wakes are complex; they involve the interactions of three shear layers in the same problem, namely a boundary layer, a separating free shear layer, and a wake. As has been recently remarked by Roshko (1992), “the problem of bluff body flow remains almost entirely in the empirical, descriptive realm of knowledge.” Although a ‘solution’ to this problem is elusive, our knowledge of this flow is extensive. In the case of the circular cylinder wake alone, there have been literally hundreds (possibly thousands) of papers. This wealth of papers is in part due to the engineering significance of cylinder flow, and in part due to the tempting simplicity of setting up such an arrangement in an experimental or computational laboratory. Rather than attempt here to describe the vortex dynamics in both unseparated and separated wakes for all the different types of 3-D and nominally 2-D body shapes, an overview will be presented of the vortex dynamics phenomena in the wake of a circular cylinder, over a wide range of Reynolds numbers.