An experimental assessment of analytical blockage corrections for turbines

Abstract

In laboratory experiments involving wind or water turbines, it is often desirable to correct measured performance for the effects of model blockage. However, there has been limited experimental validation of the analytical blockage corrections presented in the literature. Therefore, the objective of this study is to evaluate corrections against experimental data and recommend one or more for future use. For this investigation, we tested a cross-flow turbine and an axial-flow turbine under conditions of varying blockage with other non-dimensional parameters, such as the free-stream Reynolds and Froude numbers, held approximately constant. Increasing blockage improved turbine performance, resulting in higher thrust and power coefficients over a larger range of tip-speed ratios. We used these experimental data to assess the effectiveness of multiple analytical blockage corrections for both turbine types. Of the corrections evaluated, the two based on measured thrust performed best. These corrections were more effective for the cross-flow turbine than the axial-flow turbine. We attribute this result to changes in the local Reynolds number caused by increasing blockage, an effect not captured by the analytical theory. For both turbines, the corrections performed better for thrust than power, which is consistent with the assumptions that underlie the analytical theory.