Evaluation and CFD Based Improvements of Reactive Reversible Blade Turbine

A Reactive Reversible Blade Turbine (RRBT) is a cross-flow type turbine design with multiple movable blades that pivot around their local axes to hydraulically balance the blade forces while passing through the negative drag portion of the flow regime. The RRBT allows the blades to react to the negative drag and freely rotate in a way that hydraulically balances the pressure loading. The blades “slice” through the water in a reverse motion, returning to a neutral position and resting against a stop, resulting in reduced resistance on the opposite side of the turbine shaft during rotation. This allows for a significant reduction of the negative drag during the single rotation of the turbine, which improves the power coefficients compared to the current state of the art and allows the turbine to operate at a slow-moving current. Although the design is simple, there is a broad design optimization space that can impact the performance and development of this turbine for various applications. This paper focuses on developing a transient numerical model using a moving mesh approach of a single blade to characterize the flow dynamics and performance estimation. The predicted power coefficient (Cp) of 0.219, using computational fluid dynamics (CFD), aligns well with the experimentally measured value of 0.2 at a 0.32 Tip Speed Ratio (TSR). Further investigation focuses on gaining a deeper understanding of turbine performance concerning changes in blade profile, blade angles, blade widths, and scaling effects. The design space exploration study reveals that the blade angle has a substantial impact on turbine performance, particularly in shifting the peak power coefficient with the TSR. As the blade angle increases, the power coefficient rises, peaking at around 72°, followed by a decrease as the blade angle further increases. The Reynolds number scaling also indicates an approximately 20% increase in peak Cp due to the increased hydrodynamic size for the scaling from 1X to 5X. It is essential to note that these findings are based on the analysis of a single blade, and additional investigation and experimental validation are necessary to comprehensively assess the performance of the proposed design modifications.