Wind tunnel testing and improved blade element momentum method for umbrella-type rotor of horizontal axis wind turbine

The umbrella-type rotor concept for horizontal axis wind turbine is proposed. The rotor allows blades to fold along the hinge which is fixed at the hub. The blade pitching and rotor coning are coupled as the hinge is inclined. This rotor is designed as a new approach to realize power control in high wind speed. The model-scale umbrella-type rotor with three blades was made and a rotor mechanical power testing platform was set up. Wind tunnel testing was conducted to supply data to estimate the rotor power performance. In the field of wind turbine aerodynamics theory, the blade element momentum model was improved for the umbrella-type rotor aerodynamics calculation. Comparison between wind tunnel testing data and simulation result has been made. Experiment result showed that umbrella-type rotor was effective in adjusting power output by folding blades. The highest power coefficient was 0.259 in current study. Nevertheless it dropped down to 0.06 when the blades were folded at 20°. In wind speed from 5 m/s to 9.54 m/s, a constant power output of 8.87 W was achieved. The calculated rotor power coefficient was found to be in good agreement with the experiment data. The highest average deviation was 11.81%.