Characterization of three-dimensional effects for the rotating and parked NREL phase VI wind turbine

This paper addresses some three-dimensional effects which are pertinent to wind turbine aerodynamics. Two computational models are applied to the NREL Phase VI Rotor under rotating and parked conditions, a prescribed wake based Vortex Line Method (VLM) and a Parallelized Coupled Navier-Stokes/Vortex-Panel Solver (PCS). The linking between both models of the spanwise distribution of bound circulation enables the rigorous quantification of three-dimensional effects with PCS. For the rotating turbine under fully attached flow conditions, the effect of vortex sheet dissipation and the inboard vortex sheet itself on results obtained are investigated. A quantitative analysis of both radial pumping and Coriolis effect combined, known as Himmelskamp effect, is performed for viscous as well as inviscid flow. For the parked turbine, both models are applied at various pitch angles corresponding to fully attached as well as stalled flow. For partially stalled flow, it is found that a spanwise vortex originates from the blade's upper surface close to the 40% radial station and is attached to a region of stalled flow more outboard. Results show very good agreement with experimental data in particular for the PCS model. The effect of the pitch shaft section on results obtained by PCS is investigated. Finally, a new method for extracting three-dimensional aerofoil data is proposed that is particularly suited for highly stalled flow conditions.