Abstract
In many technical applications the effect of surface roughness on the local flow as well as on integral char-acteristics is significant. Understanding and modeling their effect is an ongoing challenge as there are plenty of surface structures caused by intention, manufactur-ing, or wear which have different or even contrary ef-fects on the boundary layer flow. Scale-resolving simu-lations like direct numerical simulations are a valuable tool in this context as they provide highly-resolved view of the local effect of roughness on the flow. However, complex surface structures pose challenges to the gen-eration of commonly used body-fitted structured com-putational grids. Immersed boundary methods (IBM) are a promising tool for bypassing this challenge. In this paper the IBM implemented in the CFD-solver OpenFOAM is qualified for scale-resolving simulations of turbulent channel flows over rough surfaces by intro-ducing an additional mass-flow controller. By means of three characteristic test-cases the direct numerical sim-ulations with IBM are verified against corresponding simulations with body-fitted grids. The excellent quan-titative prediction of average flow quantities as well as turbulent statistics demonstrate the suitability of the method for the simulation of turbulent flows over arbi-trary complex rough surfaces.