Vortex shedding in rotating flows

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Abstract
A rotating tow facility whose principle element is a long acrylic channel of rectangular cross-section has been developed. A smooth flexible belt, which can be translated along the channel axis, serves as a false horizontal floor. The system is mounted on a turntable which rotates at a constant angular speed about a vertical axis. The working fluid is bounded above by a sheet of acrylic plastic which can be tilted to simulate the beta effect. Topographic features are mounted on the belt and the flow past these obstacles is made visible by utilizing the electrolytic precipitation technique and recorded by a video tape camera system which translates with the belt. A series of fplane experiments on the flow past a right circular cylinder extending from the belt to the upper bounding surface is investigated in the Reynolds number range 65 < Re < 2,300. It is shown that rotation and the cylinder aspect ratio have a strong influence on the resulting flow characteristics including the Strouhal number. Furthermore it is demonstrated that for sufficiently small Rossby and Ekman numbers and cylinder aspect ratios the vortices shed in such rotating systems are dissipated by the Ekman suction occurring along the horizontal bounding surfaces. Both laminar and turbulent cylinder wakes are observed, with the experiments indicating that the latter occur at larger Reynolds numbers than would be expected should the background rotation not be present.

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