Efficient and accurate simulations of square bar roughness using adaptive and overlapping meshes

Surface morphology determines the type of turbulence structures that lead to form drag and skin-friction drag. Several experimental studies have focused on understanding the effect of surface modifications on turbulence structures. Flow over rough walls can be simulated using body-fitted grids, adaptive mesh refinement, immersed boundary methods (IBM), or overlapping grid methods. Each method has its advantages and disadvantages. Here, we carried out direct numerical simulations of square bar roughness at Re_τ = 300, 544 and 900 using adaptive mesh refinement technique, overlapping method and immersed boundary method using the high-order spectral element code Nek5000, and discussed the effectiveness of these methods in resolving all the scales present in the flow. In particular, we analyze the capability of the methods to resolve both small-scale and larger-scale turbulent structures. The latter are extracted using proper orthogonal decomposition to identify the effectiveness of the various methods in capturing the dominant modes over the bars.