Numerical simulation of the flow behind a rotary oscillating circular cylinder

A numerical study was made of flow behind a circular cylinder in a uniform flow, where the cylinder was rotationally oscillated in time. The temporal behavior of vortex formation was scrutinized over broad ranges of the two externally specified parameters, i.e., the dimensionless rotary oscillating frequency (0.110 less than or equal to S-f less than or equal to 0.220) and the maximum angular amplitude of rotation (theta(max)=15 degrees, 30 degrees, and 60 degrees). The Reynolds number (Re=UalphaD/v) was fixed at Re=110. A fractional-step method was utilized to solve the Navier-Stokes equations with a generalized coordinate system. The main emphasis was placed on the initial vortex formations by varying S-f and theta(max). Instantaneous streamlines and pressure distributions were displayed to show the vortex formation patterns. The oscillatory forcing was in the vicinity of the lock-on range, which can be applied to how feedback control afterwards. The vortex formation modes and relevant phase changes were characterized by measuring the lift coefficient (C-L) and the time of negative maximum C-L (t_(CLmax)) with variable forcing conditions. (C) 1998 American Institute of Physics.