CFD simulations and evaluation of applicability of a wall roughness model applied on a NACA 633‐418 airfoil

The implementation of a model to simulate distributed surface roughness, which is the new k−ω extension by Knopp et al. into the DTU Wind Energy in‐house CFD Reynolds‐Average Naviar Stokes solver EllipSys, was validated against wind tunnel experiments conducted in the Laminar Wind Tunnel of the Institute of Aerodynamics and Gas Dynamics, University of Stuttgart. The effort was to predict the aerodynamic penalty of five cases of leading edge roughness applied to a NACA 633‐418. Three cases were sandpaper, and two cases were turbulators/zigzag tape. Simulation of the sandpaper cases showed some agreement in the tendencies of decreased lift and increased drag as a function of angle of attack. However, the magnitudes of the aerodynamic changes were predicted and underestimated the lift and overestimated the drag. Modeling the zigzag tape using the roughness model was not successful, because the influence from the model was too small. The simulated zigzag tape hardly deviated from the fully turbulent simulation, so when using the model in its current form, one should be aware of its limitations.