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

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.

Automated summary

This paper investigates the impact of surface roughness on forces over a cylinder and vortex patterns at low Reynolds numbers. The study uses a novel immersed boundary method to capture small recirculation zones trapped inside roughness elements on the cylinder surface. The results show that the presence of vortices significantly reduces skin-friction drag, and higher roughness height leads to better lock-in phenomena at lower oscillation frequencies. However, the shedding modes of the vortices are not sensitive to surface roughness.