Investigation of the NREL phase VI experiment with the incompressible CFD solver THETA

Abstract

DLR's incompressible flow solver THETA is introduced for wind turbine applications on the isolated NREL phase VI Unsteady Aerodynamic Experiment rotor. The optimization of parameter settings for the prediction of attached and separated flows on the rotor is performed, including time step size, spatial discretization scheme, turbulence models and Chimera overset grid technique. Afterwards, a systematic study on the pressure distributions, rotor thrust and rotor torque for experimental series S, I and J is performed. The accuracy of results for wind velocities between 7 and 25 m/s, covering attached, partly separated and deep stalled flow conditions, is discussed. While good to excellent agreement between THETA sectional pressure distributions and the experimental reference data is achieved in attached flow and deep stall configurations, more efforts are needed to predict partly separated flow cases with comparable accuracy. A code-to-code comparison with DLR's compressible flow solver TAU enabled the quantification of differences in pressure prediction because of the use of incompressible and compressible flow solvers