Effect of aspect ratio on cross-flow turbine performance

TL;DR

This study experimentally examines how the aspect ratio affects the performance of a straight-bladed cross-flow turbine, revealing invariance within tested ranges and emphasizing the importance of controlled experimental conditions.

Contribution

It provides the first systematic experimental analysis of aspect ratio effects on cross-flow turbine performance under controlled conditions.

Findings

Coefficient of performance is invariant across tested aspect ratios (0.95-1.63).

Froude number variation influences performance, highlighting experimental design importance.

Minimal blade-support interactions contribute to performance invariance.

Abstract

Cross-flow turbines convert kinetic power in wind or water currents to mechanical power. Unlike axial-flow turbines, the influence of geometric parameters on turbine performance is not well-understood, in part because there are neither generalized analytical formulations nor inexpensive, accurate numerical models that describe their fluid dynamics. Here, we experimentally investigate the effect of aspect ratio - the ratio of the blade span to rotor diameter - on the performance of a straight-bladed cross-flow turbine in a water channel. To isolate the effect of aspect ratio, all other non-dimensional parameters are held constant, including the relative confinement, Froude number, and Reynolds number. The coefficient of performance is found to be invariant for the range of aspect ratios tested (0.95 - 1.63), which we ascribe to minimal blade-support interactions for this turbine design. Finally, a subset of experiments is repeated without controlling for the Froude number and the coefficient of performance is found to increase, a consequence of Froude number variation that could mistakenly be ascribed to aspect ratio. This highlights the importance of rigorous experimental design when exploring the effect of geometric parameters on cross-flow turbine performance.