Assessment of RANS-type turbulence models for CFD simulations of horizontal axis wind turbines at moderate Reynolds numbers

Nowadays, numerical simulations of wind turbines based on the Reynolds-averaged Navier-Stokes (RANS) formulation are becoming, in terms of computational cost, increasingly more viable tools for geometry optimization and design. Nevertheless, a judicious use of RANS-type methods is still required to guarantee acceptable accuracy at manageable computational cost. Here, we assess the accuracy and cost of several well-known turbulence models (Spalart-Allmaras, k - epsilon, k - omega SST, along with transitional modelling) with and without a zigzag tape modelling for a representative horizontal axis wind turbine within a range of moderate Reynolds numbers (Re approximate to 3 x 10(5) to 8 x 10(5)). This range allowed for the assessment of turbulence models under various complex flow conditions. Significant differences in performance have been found and, for a notable portion of the test cases, the k - epsilon model was able to deliver good results (similar to k - omega SST results) with a considerably coarser mesh. This suggests that k - epsilon, although often recognized as less accurate than k - omega SST, might actually be more efficient for wind turbine simulations. Also, although the best results came only with a coupled transition model which required a higher computational cost, this increase in cost is not exceedingly high and might allow for this model's usage in later design stages. Accordingly, the present study is a valuable source for future wind turbine simulations and design and we hope that it fosters further developments in the field.