Investigation on the performance of a novel forward-folding rotor used in a downwind horizontal-axis turbine

A novel forward-folding rotor (Downwind Forward-Folding Rotor, DFFR) used in a downwind horizontal axis turbine is presented in this paper. This novel wind turbine is designed to align the combination of gravitational, centrifugal, and thrust forces along the blade path, which can result in primarily tensile loads instead of cantilever loads on the blades. The power performance of the DFFR is validated to have no significant degradation, compared with that of a conventional rotor. The DFFR blades fold forward at a power-limited condition, which induces the change of the blade pitch angle and cone angle and thus maintains a constant power output. HAWT prototypes with different fold angles and the corresponding power coefficients were investigated in a wind tunnel. It is found that the maximum power coefficient decreases by 72.8% when the blades fold from 25 degrees to 0 degrees. The fold angle control strategy maintaining constantly the rotor power output at 3.95 W was acquired based on the experiment data. Moreover, a brief comparison of blade root bending moment between the DFFR and a utility-scale rotor is presented, indicating that the peak blade root bending moment can be reduced by 24.1% by the blade forward folding method. (C) 2019 Elsevier Ltd. All rights reserved.