Impact of Blade Mounting Structures on Cross-Flow Turbine Performance

Abstract

Cross-flow turbines convert fluid kinetic energy to rotational mechanical energy via blades rotating about an axis perpendicular to free stream direction. These turbines may be further sub-divided into those that generate torque from lift on foils (e.g., Darrieus rotors) and those that generate torque from drag (e.g., Savonius rotors). Despite historical concerns of low performance and structural failure due to fatigue, lift-based cross-flow turbines have experienced a resurgence of research and commercial interest in recent years and hold promise for urban1 and offshore2 wind applications. Modern experimental and computational techniques have enabled substantial increases in power performance3 and suggestions that optimized arrays may be able to extract more power per area than arrays of axial-flow turbines4. Drag-based cross-flow turbines are also an area of active research5, but are not the focus of this investigation and recent developments (e.g., Plourde et al.6) are not discussed here. In addition to wind applications, cross-flow turbines have several features that make them a promising alternative to axial-flow (horizontal-axis) turbines when operated in marine or river currents. First, their typically rectangular form factor is well-suited for the geometry of shallow tidal and river channels, allowing for the construction of higher blockage ratio turbine arrays that could boost array performance7 . Second, the maximum blade velocity of cross-flow turbines is generally lower than equivalently sized axial-flow turbines, reducing the risk of blade cavitation and potential harm to aquatic fauna through collision or acoustic emissions8 . Third, cross-flow turbine operation is either bi- or omni-directional, depending on the axis orientation eliminating the need for active yaw control in oscillating tidal currents.