Effect of flow confinement on the hydrodynamic performance of a fully-passive oscillating-foil hydrokinetic turbine

The influence of flow confinement on the hydrodynamic performance of a fully-passive oscillating-foil turbine prototype was investigated experimentally at a Reynolds number of 19,000. Quantifying confinement effects is important for comparison between model-scale experiments and full-scale turbine performance. The kinematic parameters and energy harvesting performance of the turbine were measured at eight confinement levels, ranging from 33% to 78%. Planar particle image velocimetry (PIV) was used to observe the timing of leading-edge vortex (LEV) formation and shedding, which was used to relate the flow physics to the turbine performance. The efficiency and the power coefficient increased with increasing confinement, as is expected, due to the increased effective velocity incident upon the turbine. At the highest level of confinement, the turbine performance dropped due to the shift in kinematic parameters associated with the close proximity to the confining walls.