A Modified Beddoes–Leishman Model for Unsteady Aerodynamic Blade Load Computations on Wind Turbine Blades

Abstract

A modified version of the Beddoes–Leishman (BL) dynamic stall model is presented. A novel approach was applied for deriving the effective flow separation points using twodimensional (2D) static wind tunnel test data in conjunction with Kirchhoff's model. The results were then fitted in a leastsquares sense using a new nonlinear model that gives a better fit for the effective flow separation point under a wide range of operating conditions with fewer curve fitting coefficients. Another model, based on random noise generation, was also integrated within the BL model to simulate the effects of vortex shedding more realistically. The modified BL model was validated using 2D experimental data for the S809 and NACA 4415 aerofoils under both steady and unsteady (oscillating) conditions. The model was later embedded in a freewake vortex model to estimate the unsteady aerodynamic loads on the NREL Phase VI rotor blades consisting of S809 aerofoils when operating under yawed rotor conditions. The results in this study confirm the effectiveness of the proposed modifications to the BL method under both 2D and threedimensional (3D) (rotating) conditions.