On the formation and shedding of vortices from side-wall mounted obstacles in rotating systems

Abstract

The flow of a homogenous, incompressible, rotating (vertically upward) fluid past cylinders of triangular and semi-circular cross-section mounted on either the left or right wall (facing downstream) of a channel is investigated experimentally. The pertinent system parameters are the Rossby and Ekman (or Reynolds) numbers and the obstacle width to fluid depth ratio. The experiments indicate that the shedding of tip eddies from the triangular obstacle leads to a rather complex wake motion which is critically dependent on the system parameters. For certain parameter combinations the tip eddies advect downstream as single entities while in other regions of parameter space two or more eddies merge and advect downstream as large-scale eddy structures. The Strouhal numbers for both the shedding of the tip eddies as well as of the large-scale structures are measured as functions of the system parameters. Measurements of the dimensionless size of the large-scale starting eddies are made as functions of a dimensionless time and other system parameters. It is shown that eddies formed in the lee of obstacles mounted on the right (anticyclonic) tend to shed more quickly, other parameters being fixed, than those on the left (cyclonic). Measurements of the dimensionless vorticity of the cores of the large-scale structures at a fixed dimensionless time indicate that, within the accuracy of the experiments and for the range of parameters considered, this quantity is independent of the Rossby and Reynolds numbers and the side to which the obstacle is mounted. Finally some of the experimental flow patterns are shown to be similar to a recent observation of a southeastward ocean current past the western tip of Grand Bahama Island.