A Snortland, B Polagye, O Williams, Proceedings of the 13th European Wave and Tidal Energy Conference, 1-9
Phase-averaged 2D planar PIV data for an optimal and sub-optimal tip-speed ratio (π = π.π and 1.9, respectively) is captured over the upstream and downstream sweep of a two-bladed, straight-bladed cross-flow turbine. The azimuthally varying near-blade hydrodynamics are examined in concert with phase-averaged performance data. Both the near-blade and near-wake hydrodynamics are shown to be highly dependent on tip-speed ratio and azimuthal position. The implications of observed hydrodynamics on power production are discussed. The duration and severity of flow reversal and detachment on the blades appear to be critical to overall turbine performance, with strong and persistent stall and vortex interactions occurring for most of the turbine rotation for π = 1.1. This may lead to forces that outweigh any increases in lift production from the leading-edge vortex that forms early in the rotation. Upstream blade vortex shedding is significantly delayed for π = π. π . This, combined with a weakly stalled downstream blade, significantly increases turbine performance. Differences between flow patterns observed in this study and prior work suggest an influence of Reynoldβs number.