Insights into the flow dynamics and rotor performance of a Savonius turbine with dynamic venting using controllable flaps

Abstract

The drag-driven vertical-axis turbines with semicircular rotor blades, commonly known as Savonius turbines, remain potentially beneficial to extract renewable energy from wind and water streams, especially in terms of their practicality to provide low-cost solutions to rural areas. However, they suffer drawbacks due to the negative torques on their returning blades. We propose a novel solution by dynamically venting out these returning blades using controllable flaps, which retained its omnidirectional capability. Results from unsteady numerical simulations showed that the vented rotor attained a maximum average power coefficient ( CP) of 0.275 at the tip-speed ratio (TSR, symbolized as λ) of 0.9, which was 21.7% better than that on the unvented rotor. Furthermore, the proposed dynamically-vented blades produced large improvements in the average torque coefficient ( CT), with maximum gains of 38.3% on the returning blade at ᵰ6; = 0.4 and 24.8% on the full rotor at ᵰ6; = 1.0, relative to those on the unvented rotor. The controlled dynamic venting was beneficial because it modified the pressure distributions surrounding the returning blade, and changed the flow structure downstream of the vented blade that improved the torque on the subsequent blade entering the returning side. Elucidation on the flow dynamics revealed that the flows were vented outward through the flap aperture onto the convex side of the returning blade, rather than inward into its concave side, as initially hypothesized.

Investigations on the wave performance of Savonius turbine operating under initial phase-locked strategy

“…Chan [24] used an evolutionary-based genetic algorithm and computational fluid dynamics (CFD) simulations to optimize the blade shape. Fatahian [25] introduced an innovative solution that involves the dynamic venting of these returning blades through controllable flaps while preserving their omnidirectional capability. Yao [26] explored the effect of parameters concerning different flow velocities.…”

Performance analysis of an idealized Darrieus–Savonius combined vertical axis wind turbine

“…They are compatible with omnidirectional installation and low-cost maintenance. A Savonius rotor is capable of self-starting at low wind speeds, [1][2][3] and the H-type Darrieus rotor can operate with the optimum tip speed ratio (TSR) range of 2.5-4.5, achieving a high power coefficient. [4][5][6][7] In contrast to the single Darrieus rotors, the Darrieus-Savonius combined vertical axis wind turbine (hybrid VAWT) was designed to possess high starting torque.…”