Effect of turbulence models on predicting HAWT rotor blade performances

Abstract

The effect of turbulence models on predicting the aerodynamic performance of horizontal-axis wind turbine (HAWT) rotor blades has been investigated. The flow fields around the 2-D airfoil and the 3-D blade of the NREL phase VI wind turbine rotor have been analyzed, and the results are compared between a correlation-based transition model and two other fully turbulent models. The turbulence models selected are the Spalart-Allmaras fully turbulent one-equation model, the k-omega SST fully turbulent two-equation model, and the gamma - (Re-theta t) over tilde transition model. A vertex-centered finite-volume method based on an unstructured mesh technique was used to discretize the governing Navier-Stokes equations. The inviscid fluxes were calculated by using 2(nd) order Roe's FDS, and the viscous fluxes were evaluated in a central-differencing manner. For the time integration, an implicit method based on the Gauss-Seidel iteration was used. The results showed that the gamma - (Re-theta t) over tilde transition model well captures the laminar separation bubbles on the surface of the airfoil and the blade, and these separation bubbles trigger the separation-induced transition as the laminar flow separates and re-attaches as turbulent. The separation bubbles change the flow pattern on the surface of the airfoil and on the blade, and the pressure and skin-friction distributions are also changed abruptly across the laminar-turbulent transition. With properly predicted boundary-layer transition, the results of the gamma - (Re-theta t) over tilde transition model match well with the experiment. However, the results of the fully turbulent models deviate from the experiment due to the lack of the ability of capturing the boundary-layer transition. The adoption of a proper transition turbulence model is essential for the accurate prediction of the aerodynamic loads and also the rotor performance for horizontal-axis wind turbines.