Abstract
In the present work, a computationally efficient engineering model for the aerodynamic load calculation of non-planar wind turbine rotors is proposed. The method is based on the vortex cylinder model, and can be used in two ways: either as a correction to the currently widely used blade element momentum (BEM) method, or used as the main model, replacing the BEM method in the engineering modelling complex. The proposed method needs the same order of computational effort as the ordinary BEM method, which makes it ideal for time-domain aero-servo-elastic simulations. The results from the proposed method are compared with results from two higher-fidelity aerodynamic models: a lifting-line method and a Navier-Stokes solver. For planar rotors, the aerodynamic loads are identical to the current BEM model when the drag force is excluded during the calculation of the induced velocities. For non-planar rotors, the influence of the blade out-of-plane shape, measured by the difference of the load between the non-planar rotor and the planar rotor, is in very good agreement with higher-fidelity models. Meanwhile, the existing BEM methods, even with a correction of radial induction included, show relatively large deviations from the higher-fidelity method results.
Highlights
The blade element momentum (BEM) method has long been dominant in the low-fidelity aerodynamic modelling of horizontal15 axis wind turbines
The method is based on the vortex cylinder model, and can be used in two ways: either as a correction to the currently widely used blade element momentum (BEM) method, or used as the main model, replacing the BEM method in the engineering modelling complex
By comparing the results from the three low-fidelity models with higher-fidelity models, it will be highlighted to which extent the influence of the non-planar rotor geometry can be correctly modelled by each of the lower-fidelity models. 7.1 Test cases 10 There are five different wind turbine blades used for the comparison, all of them are based on the IEA-10.0-198 10 MW reference wind turbine (RWT) (Bortolotti et al, 2019)
Summary
The blade element momentum (BEM) method has long been dominant in the low-fidelity aerodynamic modelling of horizontal axis wind turbines. A low-fidelity model that could capture the most important features of the aerodynamics of non-planar rotors, while maintaining approximately the same level of computational effort as the current BEM methods, would be of great value to both the scientific and the commercial wind turbine communities. Both for the design optimization as well as for the aeroelastic simulations. 20 Apart from the momentum theory, which effectively only applies to a planar rotor disc, it is possible to calculate the induced velocity, including the radial component, from analytical equations at each blade section with the superposition of vortex cylinders.
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