Influence of rotor geometry on the performance of high-blockage cross-flow turbine arrays

Cross-flow turbines show great promise for extracting power from river and tidal currents due to their ability to achieve high blockage. In these flows, confinement from the channel boundaries and thrust on the turbine cause accelerated flow through the rotor, which increases the turbine's efficiency. Although the effects of blockage on turbine performance are well documented, the design of cross-flow turbine rotors to best harness these effects has received little attention. Here, we experimentally investigate how rotor geometry interacts with confinement to influence the performance of a cross-flow turbine array. We consider 45 unique rotor geometries by varying three parameters: the chord-to-radius ratio, the number of blades, and the preset pitch angle. The performance of each rotor geometry is evaluated at blockage ratios of 35%, 45%, and 55% using a laboratory-scale array consisting of two identical, counter-rotating turbines. Across the tested blockages, the chord-to-radius ratio and preset pitch angle are found to affect performance in similar ways to that observed in prior studies of single turbines at low blockage. However, as the blockage ratio increases, geometries with more blades outperform their counterparts with fewer blades, indicating that turbines with higher thrust coefficients may be preferable for high blockage settings.