Power performance and self-starting features of H-rotor and helical vertical axis wind turbines with different airfoils in turbulence

•Helical VAWTs had poorer power and self-starting performance than H-rotor ones.•Dynamic stall of a helical blade would not occur simultaneously for all blade elements.•As I increased, fatigue issues of H-rotor VAWTs became much severer than helical ones.•Self-starting performance of VAWTs with NACA4418 greatly improved in turbulence.•Recommendations for the design of VAWTs in built environments were provided. Wind tunnel tests were conducted to systematically assess the aerodynamic performance of both H-rotor and helical vertical axis wind turbines (VAWTs) in smooth and turbulent flows. The effects of airfoil section and pitch angle β on the power and self-starting performance were examined for both types of turbines. The helical turbine had a wider operating range of tip speed ratios (TSR λ) and much lower power performance than its H-rotor counterpart. This phenomenon was attributed to the flow deflection of helical blades due to their three-dimensional features, as well as that dynamic stall of a helical blade would not occur simultaneously for all blade elements. The helical turbine did not exhibit notably improved self-starting performance despite of the high manufacturing cost. Moreover, the start-up process was analyzed by using the static torque coefficient CT of both single-bladed and three-bladed turbines. It was found that turbulence intensity exercised a significant impact on CT. Turbulence would cause serious fatigue issues for H-rotor turbines and change the driving mechanism of helical turbines though it enhanced the self-starting performance. Recommendations were finally provided for the design of VAWTs in built environments.