Aerodynamic performance of a wind-turbine rotor by means of OpenFOAM

Sammanfattning: In order for wind-farm operators to deal with challenges regarding their fleet management, it is useful for them to estimate their units’ performance for different conditions. To perform such estimations, Computational Fluid Dynamics (CFD) may be used. This project focuses on the development of a CFD model for the aerodynamic analysis of wind turbine rotors, depending on their surface roughness. The work has been carried out in collaboration with the KTH Royal Institute of Technology and the Vattenfall AB R&D department. The open-source software OpenFOAM has been used to develop the desired model. A rigid body incompressible steady state, Reynolds-Averaged Navier-Stokes equations, k – ω SST CFD case has been set up. The NREL 5-MW rotor geometry has been used and the effect of four different surface roughness height values {1mm, 0.5mm, 100 μm, 30 μm} on its aerodynamic performance has been investigated for an incoming wind velocity of 10m/s. The referred roughness height values have been applied on the whole rotor surface. A 120° wedge type computational domain of unstructured mesh has been developed for the present simulations. The results indicate that a roughness-height increase leads to earlier flow separation over the blade suction side and increases the turbulent area of the boundary layer. That leads to a decrease for the extracted Torque and the Thrust force on the wind turbine rotor. Moreover, it is concluded that the rotor aerodynamic performance is more sensitive to low roughness heights rather than to high ones.