10th European Conference on Turbomachinery Fluid dynamics & Thermodynamics
The present study investigates the effect of anistropic surface roughness on flow losses using Large-Eddy-Simulation (LES) and compares the results to a model based on the equivalent sand grain roughness. For this comparison models of surface roughness are built from measurements of real roughness to isolate the effect of anisotropy for which two orthogonal main flow directions with respect to the anisotropy of the surface are investigated. For these two directions an equivalent sand grain roughness height is calculated using the roughness element shape and density parameter. The shift of the velocity distribution is then predicted by using a roughness function and compared with the results of the LES. Furthermore, the rough and smooth-wall velocity distributions are compared with each other in velocity defect form to check the Reynolds number similarity hypothesis. Both comparisons show a good agreement thus con- firming with LES that the simple model of equivalent sand grain roughness is an appropriate method to predict the influence of anisotropic surface roughness on skin friction.