Impact of harmonic pitch functions on performance of Darrieus wind turbine

Wind power is known as a promising renewable energy source without any environmental pollution. Increasing efficiency of wind turbines plays a vital role in wind energy applications, approving their high efficiency and cost-effectiveness. Variable pitch angle approaches are one of the best strategies for improving the performance and self-start ability of Darrieus turbines and delaying the start of dynamic stall phenomena. However, although this method has been successfully used on several occasions, it has not yet been investigated for various complicated variable pitch functions in different amplitudes. Therefore, the present study analyzed the relationship between the angle of attack and self-starting performance of H-type vertical axis wind turbine. Four pitch functions (cases 1, 2, 3 and Sinusoidal pitch) with four amplitudes; 0 degrees, 3 degrees, 10 degrees, and 20 degrees were selected, and two-dimensional CFD (Computational Fluid Dynamics) modeling was developed to predict flow behavior around the turbine blades. The results showed that the best variable pitch function could reduce the blade angle of attack in the upstream phase while increases the angle of attack in the downstream stage. In all cases, the amplitude of 3 degrees has an excellent performance compared to other amplitudes. Also, compared to other pitch angles, Case 1 could reduce the time required for starting and with an increase of 34% in power, so it is strongly recommended for implementing in conventional turbines. Simulations also indicated that in azimuth angles between 90 degrees and 100 degrees, and between 45 degrees and 60 degrees turbine has the best and worst self-starting performance, respectively. (C) 2019 Elsevier Ltd. All rights reserved.