Computational Investigation of Cambered Blades and Virtual Camber in Cross-Flow Turbines

This research computationally investigates how cambered blades interact with the virtual camber induced in cross-flow turbine blades. Most cross-flow turbines use uncambered airfoils, likely due to the symmetries in the change of angle of attack over a complete rotation. Unlike axial-flow turbines, flow is curvilinear relative to the rotating airfoil, so an equivalent airfoil in rectilinear flow has virtual camber, changing the lift produced and relative angle of attack. In this study, single-bladed turbines with camber of up to ±3% are simulated using URANS and LES models for a range of tip-speed ratios and chord-to-radius ratios. Results are validated against experimental performance and PIV data. It is shown that camber affects the turbine performance at different parts of the cycle, depending on the direction of concavity of the camber line. This is due to camber augmenting both the lift produced by the blade and the timing of leading-edge vortex formation. It is also shown that the effects of camber are dependent on tip-speed ratio and chord-to-radius ratio, since these are the main parameters that influence the virtual camber effect. The results of this work may be used to improve the geometry of cross-flow turbines for optimal performance and control strategies.