Parametric Experimentation with Cross-Flow Turbines

Abstract:

Cross-flow turbines are free-stream kinetic energy converters that operate with an axis of rotation perpendicular to the direction of water flow. Because they can be deployed in high-blockage configurations, cross-flow turbine arrays have the potential to exploit both the kinetic and potential energy in moving water and operate, on an array basis, more efficiently than sparse arrays of axial-flow turbines. However, because their unit efficiency is lower, cross-flow turbines have received less commercial attention than axial-flow turbines and parametric studies of experimental performance are limited.

We present the results of performance testing for a set of fixed-pitch cross-flow turbines. The aspect ratio of the turbines are held constant while number of blades, preset blade pitch angle, blade helix angle, and blade profile are parametrically adjusted. Turbine performance is characterized using torque control in a laboratory flume at moderate blockage ratio and a diameter-based Reynolds number on the order of 10⁵. In addition to power performance, acoustic Doppler velocimeters on a computer-controlled gantry system are used to characterize the wake structure. Results demonstrate that turbine performance is strongly sensitive to the preset blade pitch angle, with a positive (outward) blade pitch substantially increasing peak efficiency relative to neutral pitch and negative (inward) blade pitch substantially degrading peak efficiency. The relevance of these studies to high-efficiency turbine arrays are also discussed.