Numerical optimization of pre-swirl stators for horizontal axis hydrokinetic turbines

Abstract

Hydrokinetic turbines are an important element of the world's future renewable energy portfolio, with applications in both river (unidirectional) and tidal (bidirectional) situations. However, use is presently limited, due in part to typically low turbine efficiency. This project focused on improving horizontal axis turbine performance through the use of pre-swirl stator blades. Pre-swirl stators alter the turbine inlet flow so as to maximize the blade lift in the rotational direction. The increased lift leads to greater torque and power output from the turbine. The number of stator blades, chord length, and position relative to the turbine were fixed based on parametrics in the propeller literature. The remaining important stator parameters were the cross-sectional shape and the angle of attack. The shape was selected by considering several standard foil shapes and selecting the ones with the highest stall angle and highest lift/drag ratio. Numerical flow simulations were run with the selected foils at various angles of attack to determine the velocity at the turbine location and the streamline flow around the blade. The optimal angle of attack was the one which produced an inflow angle in the desired range, with the highest velocity magnitude. Following determination of the optimal foil shape and angle of attack, a 3D model of the shroud with stators was created in SolidWorks and analyzed for future experimental testing.