Numerical and Experimental Investigation of Flow Past a Freely Rotatable Square Cylinder

This work deals with the response of a square cylinder free to rotate in a uniform flow. The two-dimensional, incompressible, time-dependent Navier-Stokes equation for flow around a fixed-cylinder are numerically solved for Reynolds numbers up to 250. The static rotational stability of the cylinder is analysed by considering moments around the fixed cylinder at different angles to the flow. The separation pattern and resulting wake are also investigated. Experiments are conducted on fixed and freely rotatable cylinders in the range of Reynolds number from 1,000 to 10,000. Variation of shedding frequency with cylinder orientation is determined for the fixed cylinder. The rotatable cylinder shows four distinct regimes of motion: a stable position where the cylinder side surfaces are parallel to the flow, periodic oscillations about this position, rotation with reversal of direction, and autorotation. Some of the dynamics of the freely rotatable cylinder can be modelled by a nonlinear, second-order differential equation. Numerical solutions of this simplified equation are compared qualitatively with experimental results.

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