Investigation of the effect of surface roughness on aerodynamic flow over a wind turbine blade

In this study, two dimensional incompressible flow over the NACA 63-415 airfoil was modelled by Computational Fluid Dynamics (CFD) method. It was aimed to find out how smooth and rough surfaces affect wind turbine performance. Numerical simulations of smooth surface condition were carried out for 6 different Reynolds numbers 10^5 <= Re <= 3*10^6 and for angles of attack 0^o <= alpha <= 20^o. Spalart-Allmaras and SST k-omega turbulence models were used for solving turbulent flow. It is found out that the optimum angle of attack is between 6^o and 8^o. Then, the rough airfoil surface simulations were performed with roughness heights between 0.1 and 0.5 mm for the optimum angles of attack. The transition SST (TSST) turbulence model was used for the rough surface simulations. The analyses of rough conditions were carried out for 7 different Reynolds numbers by adding 2.5*10^5. Results show that surface roughness can improve aerodynamic performance of the airfoil for Re=10^5. Similarly, 0.1 mm roughness height enhanced aerodynamic performance for Re=2.5*10^5. However, airfoil performance decreased with incerasing surface roughness height for Re=2.5*10^5. All surface roughness heights which were studied in this thesis negatively affected airfoil performance for the Reynolds number grater than 5*10^5. Blade Element Momentum (BEM) Theory was used to determine wind turbine power coefficient under the smooth and rough surface conditions. Results showed that the wind turbine power coefficient increased approximately 11% with increasing roughness height for Re=10^5. Otherwise, the power coefficient decreased about 32% depending on the roughness height for 5*10^5 <= Re <= 3*10^6.