Rotational effects on the aerodynamics and aeroacoustics of wind turbine airfoils

This paper describes numerical simulations of the effects of rotation on the sectional performance characteristics of wind turbine airfoils. In the present paper, only sectional calculations are performed, but in three dimensions. However, the equations are not averaged in the radial direction. Instead, a quasi-periodic behavior is assumed in the spanwise direction that allows for a spanwise flow to develop. The present sectional simulations provide comparisons between non-rotating and rotating cases. It is argued that this gives insight into the effects of rotation on the airfoil performance characteristics, especially at high angles of attack and stalled conditions, without the need for full rotating blade simulations, which would be computationally more expensive. The three-dimensional compressible Navier-Stokes equations in generalized coordinates are solved numerically. A short-time Reynolds averaging and Favre averaging is performed on the governing equations in order to permit the simulation of a high Reynolds number turbulent flow. Different closure schemes are used to model the additional terms that arise due to the averaging. The rotational effects are modeled by adding terms to the governing equations. The equations of conservation of mass and conservation of energy remain unchanged. A Detached Eddy Simulation used for turbulence modeling. It is based on the one-equation Spalart-Allmaras turbulence model. Three sets of simulations of the S809 airfoil at a blade spanwise location of 80 percent of the UAE PHASE VI experiment are conducted with and without rotational effects. Each set has been performed at angles of attack of 12.23, 13.22 and 15.24 degrees. The results show that the effect of rotation is to delay stall relative to the non-rotating case. Noise predictions are made using a Ffowcs Williams-Hawkings solver.