Validation of various windmill brake state models used by blade element momentum calculation

The concept of windmill brake state model is considered in this paper. Blade Element Momentum (BEM) calculation often calculates the value of thrust coefficient in windmill brake state. Unfortunately, thrust coefficient predicted by momentum theory deviated dramatically from the experimental data when the value of axial induction factor is greater than 0.5. To solve this problem and to increase the accuracy of the prediction, windmill break state model including tip loss effect must be applied to equations of thrust coefficient. The problem of interest is that which windmill break state model is suitable for the wind turbine model being simulated. The purpose of this paper is to compare the rotor power predicted by six different windmill brake state models. The aerodynamic code based on BEM theory has been implemented in Matlab and validated with the simulated result of AWT-27 wind turbine model reported by National Renewable Energy Laboratory (NREL). Six windmill brake state models to be compared are Glauert’s characteristic equation, classical brake state model, advanced brake state model, Wilson and Walker model, modified advanced brake state model, and Shen’s correction. The predicted power curves obtained from each windmill brake state model are compared to the measured power curve of AWT-27/P4. It has been shown that Shen’s correction gives the highest correlation to the measured data with r-square of 0.970 and the predicted annual energy production (AEP) is different from measured data by only 6.3%.