Optimal design of protuberant blades for small variable-speed horizontal axis wind turbine-experiments and simulations

In our previous study, it has been shown that the use of protuberances covering the whole leading edges of B-blades will enhance the performance of horizontal axis wind turbine (HAWT) under low speed rotations. However, a great loss of performance shall occur after a critical tip speed ratio is reached. The research aims to optimize the protuberance design of HAWT blades for the system to gain optimal performance under low speed rotations, whereas no significant drop of performance happens at high tip speed ratios. The optimization study was performed not only for baseline blades but also for those designed by the blade element momentum theory. For verifications, wind tunnel experiments were carried out to provide comparative data; additionally, numerical simulations were also conducted to further visualize the flow fields. The results show that the optimal leading-edge protuberances would significantly increase the HAWT performance under low speed rotations, yet no serious performance payback occurs at high tip speed ratios.