Simulation of the flow over a roughness element

Abstract

Simulations using Ansys Fluent are performed in order to study the interaction of a Blasius boundary layer developing on a flat surface with a cylindrical roughness element of small aspect ratio and a height smaller than the local boundary layer thickness. The goal of the simulations is a comparison with experiments performed in a laminar water channel by means of temperature-sensitive paint (TSP) (J. Lemarechal et al., 2018). Two cases are considered: First, the development of a Blasius boundary layer over a heated flat plate. Second, the interaction of the boundary layer with a roughness element. For the first case, the simulation results for the downstream development of the surface temperature agree with those obtained from the experiments. For the second case, the flow develops a horseshoe-shaped vortical structure around the roughness element as well as a recirculation zone directly downstream of the roughness element. Again, the flow structure observed in the simulation agrees qualitatively and quantitatively with the thermal footprint of the flow structure determined experimentally using TSP.