Rotating oscillatory flow past a cylinder

Abstract

The flow of a homogeneous, incompressible, rotating fluid past a vertical circular cylinder oscillating laterally in a uniform free stream is investigated experimentally. An a/D against λ/D flow regime diagram is developed under conditions of fixed Ekman number, E=3.6(10)−4 and cylinder aspect ratio H/D=1.0; here a is the amplitude of the cross-stream oscillation, D is the cylinder diameter, λ is the streamwise wavelength of the oscillation, and H is the fluid depth (cylinder height). Six distinct characteristic flow types are identified, including fully attached flow, eddy shedding for pure oscillatory motion (i.e., a zero free-stream current), double eddy structures, vortex shedding/merging, eddy chains, and irregular eddy shedding. For comparison purposes, experiments are also conducted in the same ranges of a/D and λ/D for nonrotating flows. The effects of rotation are found to be most important for the smaller values of a/D and λ/D. Rotation tends to induce rectified anticyclonic currents (i.e., in a direction opposite to the background rotation) near the cylinder boundary. Rotation also has the tendency to destroy the cross-streamwise centerline symmetry characteristic of nonrotating flows. Numerous flow observables are measured and, where possible, compared with scaling analyses.