Leveraging blade virtual morphing to enhance torque during start-up of H-Darrieus turbines

Small-scale H-Darrieus turbine ( HDT ) often struggles to reach self-sustained power producing speed due to low start-up torque. Low torque is sometimes manifested in the form of torque plateau or ‘ dead band ’. To improve torque development, turbine design variables such as blade chord-to-radius ratio ( c/r ) and solidity ( σ ) play critical role. To understand the effect of c/r only, this study analyses turbines with identical σ but different c/r using unsteady computational fluid dynamics ( CFD) . Results show that larger c/r enhances torque by influencing the leading-edge flow and vortex formation and convection. Two mechanisms are identified: (i) amplification of the variation of incidence angle along blade chord, effectively acting as aerofoil-camber morphing, and (ii) high blade pitch rate effect, especially at low λ (<1) where intra-cycle pitching is significant. These findings highlight the sensitivity of torque generation to c/r , offering design guidance for improving HDT start-up performance.