Aerodynamic optimization and experiment of horizontal axis wind turbine for low wind speed

The low wind speed area (below 6 m/s) in China is more than 85% of the total land area. For areas with poor wind resource and urgent supply demand for electricity, the wind turbine for low wind speed area is an effective complement of the centralized power generation, which has received wide attention both at home and abroad. Research on the aerodynamic performance of low speed wind turbines is of great significance for promoting the development of small-scale wind turbine technology to achieve a decentralized new energy strategy. To develop a horizontal axis wind turbine suitable for low wind speed region, taking a 100 W small horizontal axis wind turbine as the research object, the development of a horizontal axis wind turbine for low wind speed was investigated by theoretical and experimental approaches in this paper. Firstly, a small-scale wind turbine design and analysis system was established based on the modified blade element momentum (BEM) theory and validated with experiments. Secondly, considering the matching of generator parameters, the influences of designed tip speed ratios and designed attack angles on the aerodynamic performances of the wind turbine were analyzed. Thirdly, based on the local wind resource statistic characteristics, taking the designed tip speed ratio, the designed attack angle, the chord length and twist angle as designed variables, the global multi-objective aerodynamic optimization of a small wind turbine blade for both improving annual energy production and starting performance was executed using NSGA-II. The aerodynamic performances of the wind turbines before and after optimization were compared based on the modified BEM theory. Finally, a laboratory wind turbine performance test platform was built to carry out the aerodynamic performance experiment, and the wind turbine power outputs at different wind speeds before and after optimization were measured. Based on the above research, the main results are as follows: The designed tip speed ratio and angle of attack have significant effects on the performances of wind turbine. With the increase of the designed tip speed ratio, the power coefficient at low tip speed ratio decreases and the maximum reduction is about 58.17%; With the increase of the designed attack angle, the power coefficient at low tip speed ratio decreases and the maximum reduction is about 65.14%. The performance at high tip speed ratio obviously improves and the power coefficient is increased by 234.39% at the maximum. After the multi-objective aerodynamic optimization, the annual energy production is increased by 9.14% and the starting torque of the wind turbine is increased by 9.62%. Experimental results show that, the optimal blades have significantly higher power output than the initial blades under different electrical load conditions; The starting wind speed of the wind turbine is reduced from 3.84 m/s to 3.03 m/s. The feasibility of the optimal designed method was verified. Therefore, it can be concluded that, the multi-objective global optimization strategy of wind turbine blade put forward in this paper, combining the overall design parameters with the geometric parameters, avoids local optimization, presents a solution to the contradiction between low starting wind speed and high power output. This research provides references for the design and application of horizontal axis wind turbines for low wind speed areas. © 2018, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.