Calibration method of the k-ω SST turbulence model for wind turbine performance prediction near stall condition

The present study intends to enhance the accuracy of the k-omega SST turbulence model for numerical wind turbine simulation in stall condition. In order to achieve this purpose a calibration approach is proposed, and is applied to NREL S826 NTNU wind rotor. This method consists in adjusting the two turbulence model coefficients: a1 and beta*, which are found to be 0.8 and 0.45 respectively. Then the calculated power and thrust coefficients are compared to the experimental results. The power coefficient results revealed that the simulation relative error at the range of tip speed ratio between 3 to 6 where light stall occurs, is reduced from 17.89 % to 4.58 % by application of calibration. The effects of calibration on flow behaviour are implemented thereafter, by analysing pressure, and skin friction coefficients distribution along the blade. The limiting streamlines on the blade suction side are examined for more flow behaviour understanding. The effects on turbulent kinetic energy around the blade are also highlighted. The main important conclusions that can be made is that calibration reduce the separation zone on the blade suction side, and limits the vortex shedding strength, leading to improve the rotor efficiency and hence to improve the model accuracy.