Abstract:
For small-scale applications, VAWT (vertical axis wind turbine) offers a practical option due to its omni-directional operation and relatively easy installation and maintenance. However, the VAWT characterizes lower power coefficient CP at different tip-speed ratio (TSR) operations compared to the HAWT due to the presence of dynamic stall and associated blade-wake interaction induced vibrations. Dynamic stall occurs because of a large and periodic variation in the angle of attack (angle formed between the blade chord and relative wind speed) during rotation. In this regard, an advance VAWT rotor for a 1 kW H-Darrieus VAWT with leading edge (LE) slats has been designed and the potential improvement in dynamic stall characteristics has been investigated. A 2D unsteady CFD analysis has been performed on a baseline VAWT rotor and validated against experimental data provided by the turbine manufacturer. ANSYS ICEM CFD and Fluent packages have been extensively used for the performance simulation. In this study, K-w SST (Shear Stress Transport) model has been used to capture the near wall as far-field turbulence. The turbine rotor performance (Cp vs. TSR) along with flow separation over the rotor blades in shape of downstream wake and vorticity structures has been studied in detail. A static stall analysis is then performed on the slatted rotor airfoil. The results show an increase in the maximum lift coefficient Cl,max and delay in static stall angle αstall by 25%, respectively. Dynamic stall analysis has also been performed. A visible improvement in vortex shedding has been observed for slatted blade. The improved performance of the advance rotor eventually causes an increase in overall CP vs. TSR curve, with 12.6% increase in the CP at the design point TSR. The increase in rotor performance is a considerable advancement in an H-Darrieus type VAWT technology with better prospects for urban scale installation.
