Session Ce - Separated Flows.
ORAL session, Sunday, November 23
305, Moscone Center
Flow past a cylinder which is undergoing vigorous oscillatory rotation has been investigated with two-dimensional incompressible computational simulations using a viscous vortex method. At Re=15000, such flow has been studied to match the parameters of a low-drag experimental case(Tokumaru P. and Dimotakis P. (1991). "Rotary Oscillation Control of a Cylinder Wake", J. Fluid Mech., 224, 77-90.) that yields substantial drag reduction over the non-rotating situation, providing qualitative insights into the cause of the drag reduction. An instability arising in the oscillating shear layers appears to play a key role. Flow at lower Reynolds numbers is also simulated, revealing a drag-inhibiting effect but of lesser magnitude than observed in the high-Re experiments. Pressure distributions along the cylinder surface are used to illuminate the relationship between the wake evolution induced by the rotation and the unsteady force history. Consideration is given to the balance between the power saved due to drag reduction and the power expended to oscillate the cylinder.