Characteristics of two-dimensional flow around a rotating circular cylinder near a plane wall

We simulate a two-dimensional incompressible flow around a rotating circular cylinder near a plane wall at the Reynolds number Re=200 by using the lattice Boltzmann equation with multiple relaxation times. We investigate the flow pattern in the parameter space of the rotational rate gamma:=omega a/U and the normalized gap h:=H/D, where omega is the angular velocity of the cylinder, a and D are the cylinder radius and diameter, respectively, U is the inflow velocity, and H is the gap between the cylinder and the wall. We quantify the effects of gamma and h on the hydrodynamic forces and the frequency of vortex shedding from the cylinder. Our results indicate that two critical values of h, h(down) and h(up), exist, which depend on gamma. The flow is steady when h < h(down), while it has a wake of a regular vortex street when h > h(up). When h(down)< h < h(up), the flow is aperiodic. We observe that the mean drag coefficient C-D is a monotonically increasing function of h when gamma <= 0. When gamma > 0, C-D is no longer a monotonic function of h. The mean drag coefficient C-D varies significantly in the range h(down)< h < h(up), and so do the root-mean-square values of the lift and drag coefficients, C-D and C-L. When h > h(up), the wall effect diminishes. (c) 2007 American Institute of Physics.