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 crossflow 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. We used the resulting experimental data to assess the effectiveness of multiple analytical blockage corrections for both turbine types. Of the corrections evaluated, two are recommended. However, as these methods are based on axial momentum theory, we observe that corrections are more effective for thrust than power. We also find that increasing blockage changes the local Reynolds number, which can affect turbine performance but is not reflected in axial momentum theory.

Solidity effects on the performance of vertical-axis wind turbines

“…In addition, thrust coefficient values for this turbine often exceeded unity during the tests and so no blockage Glauert (1935), but discussed in many other works (see e.g. Bahaj, Molland, Chaplin, & Batten, 2007;Chen & Liou, 2011;Mikkelsen, 2004;Ross & Polagye, 2020). However, in all tests the low-geometric blockage of the turbine was kept constant to minimize any resulting blockage effects.…”

The effect of porosity on the drag of cylinders

“…The blockage correction presented by Maskell (1965) is not valid for porous bodies, as it assumes zero wake velocities, while various corrective models based on actuator disks (Bahaj et al 2007; Werle 2010), often used in wind engineering, are not valid for cases where the bluff-body porosity is small. A recent review of blockage correction models can be found in Ross & Polagye (2020). Although blockage will affect the magnitude of the drag coefficients, care was taken such that it would not alter the trends or the conclusions of the study.…”

Flow Field Measurement of Laboratory-Scaled Cross-Flow Hydrokinetic Turbines: Part II—The Near-Wake of Twin Turbines in Counter-Rotating Configurations

“…Later in the decade, tow tank experiments were conducted by Wosnik group for a reference cross-flow hydrokinetic turbine [6,7]. Related to this reference model, Ross and Polagye performed various experimental measurements with other smaller scaled turbine models to assess analytically models of blockage effect on cross-flow turbines [8]. Other than tow tank experiments, studies of small scaled turbines in water flumes have also been fruitful for the community.…”