Wind tunnel testing of a horizontal axis wind turbine rotor and comparison with simulations from two Blade Element Momentum codes

The results of wind tunnel tests performed on a full scale horizontal axis wind turbine with a rotor diameter of 1.2 m are presented, analyzed and compared with those predicted by WT_Perf and Qblade Blade Element Momentum (BEM) codes. The studied rotor, carved in wood, belongs to a family of wind turbines suitable for production by unskilled persons with hand tools, with more than one thousand turbines already produced. The experiments were conducted in a 2×2 m open test chamber closed circuit wind tunnel at wind speeds of 3.0; 3.7; 4.4; 5.5; 7.2; 7.7 m/s and shaft power with varying tip speed ratios (λ) was measured. The maximum experimentally obtained power coefficient (Cp) was found to vary significantly with the wind speed, between Cp=0.32 for 3.0 m/s and Cp=0.40 for 7.7 m/s. The tip speed ratio corresponding to peak power coefficient was found to vary inversely with the wind speed, from λ=6.5 at 3.0 m/s to λ=4.8 at 7.7 m/s. Comparison of the obtained wind tunnel data with the results provided by the two BEM codes was found to be good.