Performance enhancement of a Savonius wind turbine under near-wall conditions using a passive flow-responsive curtain

Savonius wind turbines are increasingly considered for urban and building-integrated applications, where installation near walls or structural boundaries is often unavoidable. Under such near-wall conditions, wall-induced flow modification can significantly degrade aerodynamic performance depending on the turbine–wall distance and wall orientation relative to the incoming flow. However, most existing flow-control devices have been designed for free-stream conditions and lack adaptability to wall-affected inflow. To address this, this study experimentally investigates the aerodynamic influence of a downstream wall and proposes a passive flow-responsive curtain–guide system to mitigate performance degradation. Results show that close wall proximity reduces power output by up to 21% due to flow blockage. However, the introduction of a passive flow-responsive guide enables autonomous stabilization of the curtain within the optimal range, yielding consistent peak power coefficient increases of 13%–36% regardless of wall orientation. Particle image velocimetry confirms that these gains arise from flow redirection and a flow-induced torque-balance mechanism. Overall, the proposed passive system provides a simple and robust strategy for urban and building-integrated Savonius wind energy applications.