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 numerical ly solved for Reynolds numbers up to 250. The static rotational stabil ity of the cylinder is analysed by considering moments around the fixe d cylinder at different angles to the flow. The separation pattern and resulting wake are also investigated. Experiments are conducted on fi xed and freely rotatable cylinders in the range of Reynolds number fro m 1,000 to 10,000. Variation of shedding frequency with cylinder orien tation is determined for the fixed cylinder. The rotatable cylinder sh ows four distinct regimes of motion: a stable position where the cylin der side surfaces are parallel to the flow, periodic oscillations abou t this position, rotation with reversal of direction, and autorotation . Some of the dynamics of the freely rotatable cylinder can be modelle d by a nonlinear, second-order differential equation. Numerical soluti ons of this simplified equation are compared qualitatively with experi mental results.