3-D time-accurate CFD simulations of wind turbine rotor flow fields

This paper presents the results of three-dimensional and time-accurate Computational Fluid Dynamics (CFD) simulations of the flow field around the National Renewable Energy Laboratory (NREL) Phase VI horizontal axis wind turbine rotor. The 3-D, unsteady, parallel, finite volume flow solver, PUMA2, is used for the simulations. The solutions are obtained using unstructured moving grids rotating with the turbine blades. Three different flow cases with different wind speeds and wind yaw angles are investigated: 7 m/s with 0° yaw (pre-stall case I), 7 m/s with 30° yaw (prestall, yawed case II), and 15 m/s with 0° yaw (post-stall case III). Results from the inviscid simulations for these three cases and comparisons with the experimental data are presented. Some information on the current work in progress towards Large Eddy Simulations (LES), including details about the viscous grid and the implementation of wall-functions, are also discussed. The inviscid results show that the flow is attached for cases I and II, with the latter having an asymmetrical wake structure, whereas there is massive separation over the entire blade span in case III. There are considerable spanwise pressure variations in addition to the chordwise variations, in all three cases. Comparisons of sectional pressure coefficient distributions with experimental data show good agreement. These three-dimensional and time-accurate CFD results can be used for the far-field noise predictions based on the Ffowcs Williams - Hawkings method (FW-H), which can provide a first-principles prediction of both the noise and the underlying turbulent flow that generates the noise, in the context of the wind turbine application.