Realistic improvements via overset meshing on a Taguchi-optimized Savonius rotor with controllable dynamic venting

Recent advancements in controllable dynamic venting have enhanced the efficiency of drag-driven Savonius turbines while preserving their omnidirectional capability, making them more viable for practical energy extraction. This study extends previous work by employing overset meshing to improve the design and functionality of controllable flaps, allowing for more realistic hinge placement and rotation. Unlike prior approaches using the sliding mesh technique, each flap is now hinged at the inner tip of its parent rotor blade. This new mechanism allows the flap to rotate inward and vent impinging flows more effectively during the returning sweep, thus reducing negative torques and improving aerodynamic efficiency. Using a Taguchi-based optimization framework and analysis of variance, three flap designs and six operational parameters were systematically analyzed to maximize power output while minimizing energy consumption. The optimal configuration—a mid-half flap design—resulted in a 29% increase in average power coefficient (Cp) at the optimal tip-speed ratio (TSR = 1.0), surpassing previously reported gains of 21% and 25%. Notably, unlike earlier studies where flow venting occurred outward, this study confirms that vented flow is more naturally redirected inward toward the concave side of the returning blades, as initially hypothesized. These findings refine the approach to dynamic venting, demonstrating its potential to reduce negative torques and enhance Savonius rotor efficiency, particularly in practical applications where omnidirectionality and low-speed performance are advantageous.