Measurement of Axial Induction Factor for a Model Wind Turbine

Abstract

Understanding the velocity field information near the rotor plane of a wind turbine at various operating conditions is very important to understanding the aerodynamic performance of the wind turbine. Investigation of these flow fields has been an important area of study in experimental fluid dynamics for the last few decades. It is more convenient and cost effective to perform experiments with scaled-down model wind turbines rather than taking measurements around a full-scale model. Along with different experimental techniques, computational models to predict the performance of wind turbines have been developing. The basis of most of the commercially available codes is the Blade Element Momentum (BEM) method. However, the applicability and performance of these codes are often questionable at different operating conditions. Therefore, it is necessary to validate these codes with different wind turbine designs under a large variety of operating conditions. In this research project, two-dimensional PIV measurements near the rotor plane of a three-bladed, horizontal axis model wind turbine were taken at six different operating conditions and at 15 azimuthal angles. The results are presented in terms of axial induction factor. The radial distribution of axial induction factor at the rotor plane was compared to the results obtained from WT_Perf, a typical BEM method. BEM fails to predict of the value of axial induction factor at the tip region for most of the operating conditions. However, the predictions are good at the root region. At the mid-span region, BEM has good predictions for operating conditions higher than the optimum operating condition, better in the optimum operating conditions and differs significantly at the operating conditions lower than optimum tip-speed ratio. The datasets obtained from the experiment will serve as a very good database for code designers for the validation of codes and development of models.