Use of quasi-3D CFD simulations to generate polar curves for blade element momentum computations

Abstract

The blade element momentum (BEM) method is an aerodynamic tool widely used for the analysis and design of horizontal axis wind turbines.The method demands as input polar curves for the airfoils of the blade sections. These curves are commonly obtained through wind tunnel measurements or two-dimensional simulations. Since it neglects rotational effects, in its original formulation, the BEM method tends to underestimate the blade loads at high wind speeds and semi-empirical models are used to correct the polar curves, accounting for these rotational effects. However, the knowledge of the relationship between the proper value of the empirical parameters needed in such models and the blade geometry or the operation condition depends strongly on the user's experience. Recently, researchers have been applying airfoil polar curves extracted from 3D simulations of realistic blade geometries. Besides the greater computational cost, the polar curves extracted in this manner are subjected to the aerodynamic influence of the three-dimensional geometric characteristics of the particular simulated blade. The investigation proposed here aims at evaluating the possibility of generating polar curves with quasi-3D Navier-Stokes simulations to be used in BEM computations. The quasi-3D simulations will account for non-inertial effects on the airfoil flow over the airfoil disregarding the 3D effects of a particular blade geometry. It is believed that an accurate and robust methodology can be developed for the aerodynamic computations of horizontal-axis-wind-turbine rotors.