Experimental Verification of Pitch Angles for Power Regulation of Variable Pitch Horizontal Axis Wind Turbine

Abstract

In this paper a variable speed variable pitch horizontal axis wind turbine (HAWT) is designed using the blade element momentum (BEM) model and experimentally tested in an open section wind tunnel. The BEM offers a fast design approach since it is essentially a twodimensional strip theory model and is used for all preliminary designs and for real time wind turbine control. Two wind turbines were designed that have the same rated power (0.45 kW). In the first design the blade is composed of a constant thickness blade (t/c = 15%). In the second design the blade is composed of a variable thickness blade varying from t/c = 25% at the hub to t/c=21% at the tip. The model results show that thick blades are less sensitive to errors in the pitch angles as the turbine switches from variable speed to variable pitch control. The thick blades were also easier to manufacture using CNC machines. Three sets of experimental results were obtained for pitch angles of -5 o , 0 o and 10 o . The experimental measurements compare favorably for the 0 o and 10 o which correspond to cases in which the power coefficient is large (order of 10%). The experimental measurements for the -5 o does not compare well with the model. This is attributed to two issues. First the blades operate in the stall regime and hence the BEM model is not valid, and second the power coefficient is relatively small (order of 1%). Overall the BEM theory compares well with experiment, with a correlation coefficient, R 2 , of 0.9.