Consideration of Aerodynamic Effects of Blade Rotation as computed with Urans in Load Simulations with BEM

Load simulations for wind turbines are often based on the blade-element-momentum theory (BEM). This theory is based on a simplification of the underlying physics of rotor aerodynamics and makes use of 2-dimensional airfoil properties. Therefore, some relevant aerodynamic effects cannot be represented with this approach. These aerodynamic effects can be stationary or dynamic and assigned either to the global rotor flow or to the local flow within the boundary layer. The stationary effects that are related to the local flow within the boundary layer can be included into BEM simulations using so called 3 dimensional airfoil tables. Semi-empirical correction models have been developed to account for the particular effect. It is shown that relying on such correction models to account for 3 dimensional flow effects in the boundary layer is not precise enough to predict the loads on modern wind turbines under certain conditions. Therefore, a method is described to account for all relevant stationary effects in the boundary layer that are related to rotor rotation in BEM-based load simulations. The presented approach makes use of 3 dimensional URANS CFD simulations of a wind turbine rotor. The URANS simulations are used to extract 3 dimensional airfoil tables that can be used in load simulations based on the BEM approach. The 3D airfoil polars are explained in detail by means of the simulated flow field.

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