Simulation of flow over a fixed and oscillating circular cylinder with different surface roughness patterns using a multi-block-multi-mesh framework immersed boundary method

Abstract

The effect of surface roughness on forces over a cylinder and the resulting vortex patterns at low Reynolds numbers are not well reported in the literature. This paper investigates flow over fixed and transversely oscillating two-dimensional rough cylinders with different roughness heights and spacing. A novel multi-block-multi-mesh framework-based immersed boundary method is developed to resolve the roughness elements over the cylinder surface, using a relatively coarser mesh at the outer domain. Small re-circulation zones trapped inside the roughness elements are captured. A drastic reduction in skin-friction drag is observed due to these vortices for both fixed and oscillating cylinders. Higher roughness height resulted in better lock-in phenomena at lower oscillation frequencies. However, the vortex shedding modes did not show much sensitivity to surface roughness.