An experimental evaluation of the interplay between geometry and scale on cross-flow turbine performance

Abstract

Cross-flow turbines harness kinetic energy in wind or moving water. Due to their unsteady fluid dynamics, it can be difficult to predict the interplay between aspects of rotor geometry and turbine performance. This study considers the effects of three geometric parameters: the number of blades, the preset pitch angle, and the chord-to-radius ratio. The relevant fluid dynamics of cross-flow turbines are reviewed, as are prior experimental studies that have investigated these parameters in a more limited manner. Here, 223 unique experiments are conducted across an order of magnitude of diameter-based Reynolds numbers ($\approx 8\times 10^4-8\times 10^5$) in which the performance implications of these three geometric parameters are evaluated. In agreement with prior work, maximum performance is generally observed to increase with Reynolds number and decrease with blade count. The broader experimental space clarifies parametric interdependencies; for example, the optimal preset pitch angle is increasingly negative as the chord-to-radius ratio increases. As these experiments vary both the chord-to-radius ratio and blade count, the performance of different rotor geometries with the same solidity (the ratio of total blade chord to rotor circumference) can also be evaluated. Results demonstrate that while solidity can be a poor predictor of maximum performance, across all scales and tested geometries it is an excellent predictor of the tip-speed ratio corresponding to maximum performance. Overall, these results present a uniquely holistic view of relevant geometric considerations for cross-flow turbine rotor design and provide a rich dataset for validation of numerical simulations and reduced-order models.

This article appeared in Hunt et al., Renewable and Sustainable Energy Reviews 206, 114848 (2024), and may be found at https://doi.org/10.1016/j.rser.2024.114848. Data supporting this manuscript may be found in the Dryad digital repository at https://doi.org/10.5061/dryad.mpg4f4r8p

References in corpus (3)

• The dynamic stall dilemma for vertical-axis wind turbines
• Analysis of dynamic stall development on a cross-flow turbine blade
• Cycle-to-cycle variations in cross-flow turbine performance and flow fields

Cited by in corpus (4)

• Influence of the downstream blade sweep on cross-flow turbine performance
• Experimental identification of blade-level forces, torque, and pitching moment for cross-flow turbines
• Performance characteristics and bluff-body modeling of high-blockage cross-flow turbine arrays with varying rotor geometry
• Experimental validation of a linear momentum and bluff-body model for high-blockage cross-flow turbine arrays