Performance characteristics and bluff-body modeling of high-blockage cross-flow turbine arrays with varying rotor geometry

Abstract

While confinement is understood to increase the power and thrust coefficients of cross-flow turbines, how the optimal rotor geometry changes with the blockage ratio -- defined as the ratio between the array projected area and the channel cross-sectional area -- has not been systematically explored. Here, the interplay between rotor geometry and the blockage ratio on turbine performance is investigated experimentally with an array of two identical cross-flow turbines at blockage ratios from 35% to 55%. Three geometric parameters are varied -- the number of blades, the chord-to-radius ratio, and the preset pitch angle -- resulting in 180 unique combinations of rotor geometry and blockage ratio. While the optimal chord-to-radius ratio and preset pitch angle do not depend on the blockage ratio, the optimal blade count increases with the blockage ratio -- an inversion of the relationship between efficiency and blade count typically observed at lower blockage. To explore the combined effects of rotor geometry, rotation rate, and the blockage ratio on array performance, we utilize two bluff-body models: dynamic solidity (which relates thrust to the rotor geometry and kinematics) and Maskell-inspired linear momentum theory (which describes the array-channel interaction as a function of the blockage ratio and thrust). By combining these models, we demonstrate that the array time-average thrust coefficient increases with dynamic solidity in a manner that is self-similar across blockage ratios. Overall, these results highlight key design principles for cross-flow turbines in confined flow and provide insights into the similarities between the dynamics of cross-flow turbines and bluff bodies at high blockage.

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in J. Renewable Sustainable Energy 17, 034501 (2025) and may be found at https://doi.org/10.1063/5.0272110. Data supporting this work is available in the Dryad data repository at https://doi.org/10.5061/dryad.1c59zw45d

References in corpus (6)

• The dynamic stall dilemma for vertical-axis wind turbines
• Effect of aspect ratio on cross-flow turbine performance
• An experimental evaluation of the interplay between geometry and scale on cross-flow turbine performance
• Analysis of dynamic stall development on a cross-flow turbine blade
• Cycle-to-cycle variations in cross-flow turbine performance and flow fields
• Influence of the downstream blade sweep on cross-flow turbine performance

Cited by in corpus (1)

• Experimental validation of a linear momentum and bluff-body model for high-blockage cross-flow turbine arrays