SANDWake3D: A 3D parabolic RANS solver for atmospheric boundary layers and turbine wakes

Abstract. Despite many recent advances, modeling wind turbine wakes using semi-empirical and analytical models still face challenges when dealing with more complicated situations involving wind shear, veer, atmospheric stratification, and wake superposition. To address these limitations, this study introduces a three-dimensional, parabolic Reynolds Averaged Navier Stokes (RANS) k-epsilon formulation which includes an atmospheric boundary layer model and an actuator disk model for turbine wakes. The full three-dimensional solution for the velocity, temperature, and turbulence variables are efficiently solved through an alternating direction implicit scheme that requires orders of magnitude less computational resources than traditional high fidelity approaches. The results of the parabolic RANS model are compared to the equivalent large-eddy simulations (LES) and semi-empirical wake models at different wind speeds under stable atmospheric conditions with veer and shear. For the single turbine wake the RANS model was able to capture the wake deficit behavior, including the wake stretching and skewing that was observed in the LES. The distribution of the wake turbulence in the RANS model also agreed with results from the higher fidelity simulations. In simulations of a two-turbine, directly waked configuration, the new RANS model was able to handle the wake superposition behavior without difficulty, and also correctly modeled the corresponding increase in wake turbulence when compared to LES. Lastly, a demonstration of the RANS model on a 9-turbine, 3 row wind farm is shown and compared to LES.