Investigation on the aerodynamic characteristics of vertical axis airfoils and the influence mechanism of pitch moment

To address the issue of strong unsteady dynamic stall during the rotation of large-capacity vertical axis wind turbines (VAWTs), as well as the lack of matching criteria between airfoil aerodynamic selection and pitch system design in engineering applications, this study conducts a comparative analysis of airfoil aerodynamic characteristics and investigates the influence of pitching axis positions on the pitching moment. A high-precision unsteady numerical model for a megawatt-scale H-type double-blade VAWT is established using the Transition SST four-equation turbulence model with consideration of flow transition, combined with sliding mesh technology. The reliability of the method is validated against classical experimental data of high-Reynolds-number ramp-type pitching dynamic stall. The aerodynamic performance of three typical airfoils (NACA0021, S1046, and DU250) is systematically analyzed at a design tip speed ratio λ = 6. Furthermore, the full-cycle characteristics of the pitching moment corresponding to seven chordwise and two radial offset pitching axis positions are examined. The results indicate that the asymmetric airfoil DU250 achieves the highest wind energy capture efficiency, with a power coefficient (C_P) of 0.410, which is 6.77% higher than that of NACA0021. However, DU250 also exhibits the largest amplitudes of torque and pitching moment. The S1046 airfoil offers the optimal balance between power generation efficiency and load stability. The position at 0.25 times the chord length is identified as the theoretically optimal pitch axis location, significantly reducing both the amplitude and fluctuation of the pitching moment. Radial offset significantly amplifies the pitching moment. This study reveals the influence mechanism of airfoil geometric characteristics on the aerodynamic performance of VAWTs and quantifies the mapping relationship between pitch axis position and pitching moment. The findings provide theoretical support for the aerodynamic optimization design of large-capacity pitch-controlled VAWTs near the design tip speed ratio.