Numerical Investigation of Fluid Flow Past a Cylinder: Effect of Surface Roughness

This study employs direct numerical simulation (DNS), combined with the Cartesian cut-cell method and quadtree adaptive mesh refinement, to systematically investigate the effects of surface roughness on the flow past a cylinder. The varying surface roughness is described mainly in terms of the wavenumber β. Results show that the non-uniform roughness disrupts the symmetry of flow structures and randomizes separation, forming a heterogeneous flow with coexisting small-scale groove vortices and large-scale side vortices. At Re=100, the drag coefficient exhibits a maximum at β=30, with a corresponding 1.48-fold increase in the peak local pressure coefficient over a smooth cylinder. The lift coefficient stabilizes between 0.375 and 0.38 for β≥20. The trend of force varies across different Reynolds number ranges. Beyond a critical roughness at Re>100, the mean drag and lift amplitude become roughness-insensitive.