Effects of near-wall grid spacing on SST-K-ω model using NREL Phase VI horizontal axis wind turbine

Investigation of the effects of near-wall grid spacing for the SST-K-ω model and study of the aerodynamic behavior of a horizontal axis wind turbine are the two goals of this paper. The NREL Phase VI is used as the aerodynamic model. Eight different cases are investigated for the near wall grid spacing study. Furthermore, one case is studied in both the SST-K-ω and the Langtry-Menter transitional models. For all cases the total number of nodes are fewer than 5000,000. Thrust forces, flow patterns and pressure coefficients are compared at different wind speeds. The thrust values of the SST-K-ω are not in a good agreement with the test results. The streamlines show that the inboard section of the blade has a severe complex 3D flow which separates at low velocities; the mid-span section stays attached for higher velocities and the outboard part has 2D-like behavior and separates as the last part. Also, for areas with complex separation, reattachment and sever spanwise flow (e.g., at the inboard section), the SST-K-ω mispredicts the pressure values. Generally, the SST-K-ω over predicts the separation by mispredicting the separation point. Besides, it is observed that Gamma–Theta transitional model behaves differently from the SST-K-ω, especially at the inner part and the results are closer to the test results.

► Different grid spacing for SST-K-ω model together with aerodynamic of NREL Phase VI are investigated.
► Results show that SST-K-ω is appropriate for fully attached or separated flows, but not for partially attached flows.
► Y-plus, expansion ratio, number of nodes inside B.L. and in streamwise directions found to be crucial factors.
► Spanwise flow is observed to be common for average and high wind speeds.
► Separation begins at very low wind speeds at inboard section and happens at higher speeds for outer sections.