Abstract
Cross-flow turbines, commonly referred to as vertical axis turbines in wind energy, are attractive options in tidal and river hydrokinetic energy capture. Since the axis of rotation is perpendicular to the flow, cross-flow turbines can be oriented vertically in a water channel, and avoid alignment and yaw positioning required of axial flow turbines. Other benefits include their scalable cross-sectional area, which is often ideal for shallow waterways. Many cross-flow turbine designs have been adapted from wind energy, and include two or more straight or helical blades, supported by various strut designs, and can vary in terms of blade chord to radius ratio, thus impacting the solidity of the turbine.
Marine energy is perhaps unique from wind energy in that rivers and tidal flows have abundant natural flow constrictions in which the waterway narrows, causing local flow acceleration, increased velocity, and significant improvement in energy capture efficiency. In addition to these natural constrictions, turbines can be arranged within the channel in close proximity to another to impose blockage, and further increase confinement and efficiency. Under these conditions, the turbine’s optimal operating conditions will vary, and there is potential for the turbine dynamics to constructively complement one another. This project explores the hydrodynamics of cross-flow turbines under these high confinement conditions using numerical simulations.
Using a two-dimensional Reynolds Averaged Navier Stokes solver, a two turbine array is spanned across a channel in a fence configuration, where the two sides of the domain are walls. Two blockage configurations are considered by increasing the width of the channel but keeping the turbine pair fixed in the same position. The performance and hydrodynamics are analyzed over a range of tip-speed ratios and operation conditions and compared against available experimental results.