Comparison of Different Solvers and Geometry Representation Strategies for Dns of Rough Wall Channel Flow

In the present study we investigate an incompressible turbulent channel flow with heat transfer at Reτ = 180 with a deterministic surface topography consisting of truncated cones. Two solvers for each of the two boundary handling strategies are considered. With Nek5000 and OpenFOAM the influence of the roughness elements is directly accounted for by an unstructured body fitted mesh, whereas Xcompact3d and SIMSON utilize the immersed boundary method (IBM) to deal with the 3D geometry. The main focus of this work is on an evaluation of the usability of the IBM and a comparison of the parallel performance of the different solvers. Since usability is an ambiguous definition, various quantities are compared: global statistics like Nusselt number and friction coefficient, one-dimensional wall-normal profiles for first and second order statistics, as well as three-dimensional averages over roughness sections. In addition, the computational effort for each method is documented.