Vortex methods to answer the need for improved understanding and modelling of tip‐loss factors

Standard blade element momentum (BEM) codes use Prandtl's tip‐loss correction which relies on simplified vortex theory under the assumption of optimal operating condition and no wake expansion. The various tip‐loss functions found in the literature are listed. A simple comparison between them shows important differences in Annual Energy Production which reveal a large uncertainty in current BEM‐based computations. A new tip‐loss correction for implementation in BEM codes has been developed using a lifting‐line code to account for the effect of wake expansion, roll‐up and distortion under many operating conditions. A database of tip‐loss corrections is established for further use in BEM codes. This model is closer to the physics of the flow and hence, a better assessment of the performance of wind turbines by this method is expected.