A numerical investigation on effects of blades with varying chord length in Darrieus vertical axis wind turbines

Energy production in dense urban areas remains a key challenge for achieving SDG7 goals. Vertical Axis Wind Turbines (VAWTs) have emerged as ideal candidates for such environments due to their compact design and omni-directional wind capture. However, low torque at lower rotational speeds and self-starting issues have hindered their transition to commercial-scale production. This research intends to address these challenges by implementing blades equipped with a novel varying chord length distribution. A good number of cases with variable chord length distributions were examined to explore the configuration with highest torque generated using 3D URANS model. The findings suggest that augmenting the chord length at the mid-span of the blade effectively postpones the initiation of dynamic stall. Conversely, a reduction in chord length in the vicinity of the blade tips contributes to the generation of attenuated tip vortices. Comparison with a simple straight bladed turbine reveals that the optimal varying chord configuration enhances performance by up to 67 % at low values of Tip Speed Ratio (TSR), particularly at TSR = 0.75, and improves self-starting capability by 21 %. These improvements, along with enhanced structural strength, make it ideal for rooftop installation.