Numerical simulation of the flow behind a rotary oscillating circular cylinder

Abstract

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⩽Sf⩽0.220) and the maximum angular amplitude of rotation (θmax=15°, 30°, and 60°). The Reynolds number (Re=U∞D/ν) 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 Sf and θmax. 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 flow feedback control afterwards. The vortex formation modes and relevant phase changes were characterized by measuring the lift coefficient (CL) and the time of negative maximum CL (t−CLmax) with variable forcing conditions.