A Detailed investigation of the Blade Element Momentum (BEM) model based on analytical and numerical results and proposal for modifications of the BEM model

Abstract

The paper presents the results of a comprehensive investigation of the BEM model based on detailed results from actuator disc simulations as well as analytical derivations. The objectives of this work has been to investigate the deficiencies in the BEM model, which is the most common engineering model for computation of the aerodynamic loads on wind turbine rotors and used widely within the industry. An additional objective has been to derive modifications to the BEM model in order to improve the accuracy of the model. Our comparisons of numerical results from the actuator disc simulations with BEM results have shown two areas of deviations. On the inner part of the rotor the BEM model overestimates the induction due to neglecting the pressure term from wake rotation. On the outer part of the rotor the tendency is opposite with an underestimation of the induction by the BEM model which seems to be an effect from expansion of the stream tubes. Two simple correction models to the BEM model were derived to account for these deviations and the results of the modified BEM model correlate very well with actuator disc results for different load distributions.