Rotating open channel flow past right circular cylinders

Abstract

The characteristics of the free stream motion in a two meter wide by ten meter long rotating free surface flow facility are discussed. Experiments on the flow past a right circular cylinder whose axis is parallel to the rotation axis are presented for the following parameter ranges: 2,500≦Re≦37,500; Ro≧1.43; 0.33≦R/H≦1.67; and 0.05≦R/S≦0.25 where Re is the Reynolds number, Ro, the Rossby number, R/H, the cylinder aspect ratio and R/S, the channel blockage factor. A flow observation technique, using free surface floats, is presented which can be used to determine the distribution of the vertical component of vorticity in eddies shed from the cylinder. Using a case study approach this technique gives a quantitative verification that in rotating systems shed cyclones have a larger maximum relative vorticity than their anticyclonic counterparts. The surface float technique also is shown to be a good approach to investigating the decay of vortices in such a free surface flow facility. Using a constant eddy viscosity model it is shown that the eddies shed from the circular cylinders, for cases in which background rotation is present, decay by Ekman suction. By defining the size of the shed eddies as the radius of the eddy at which the azimuthal velocity is a maximum relative to an observer moving with the free stream, it is shown that the anticyclones are larger than the cyclones at similar streamwise locations, other parameters being fixed. This study also presents data which show that rotation tends to result in larger Strouhal numbers than corresponding non-rotating flows. For experiments in which the inertial frequency, 2Ω, approaches the eddy shedding frequency, ω_E, the shedding frequency tends to match the inertial frequency.