Evaluation of pitch control techniques for a cross-flow water turbine
Gauthier, Timothy Andrew
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Cross-flow water turbines are complex devices that have yet to see large-scale implementation relative to conventional horizontal-axis wind turbines. While wind energy was the primary target of past investigations, water energy follows most of the same dynamic principles. However, water currents tend to be much more stable than their wind current counterparts, and many water currents exist in channels that favor the compact shape of the cross-flow turbine. These advantages have rejuvenated interest in cross-flow turbine design for marine energy generation. Computational models give engineers the ability to accurately estimate what designs work best to avoid costly field maintenance and downtime. Specifically, computational fluid dynamics uses the Navier-Stokes equations, a set of differential equations that describe the pressure and velocity fields in a fluid domain. The Reynold-Averaged Navier-Stokes turbulence model described in this work examines how controlling the pitch of water turbine blades can improve system performance and reliability. Pitch means that the blade noses up or down about the chord line which runs from leading edge to trailing edge relative to the inflow. Pitch control was originally developed for helicopter blades and is commonly used by conventional wind turbines, but pitch control for water turbines is a relatively new research area. Initial results suggest significant incremental gain in power output with pitch control up to 149%, as compared to a no-pitch case, based on a to-scale representation of the cross-flow water turbine in the Fluids and Computations Laboratory at Montana State University. Simultaneous reliability gain is observed as the force transmitted by the water to the blades is reduced by 135%; this may allow for lower cost turbine structures and streamlined hydrofoil design. Additionally, turbine wake profile visualization and blade pressure coefficient curves describe the viscous interaction both quantitatively and qualitatively. Cross-flow water turbines have the potential to become a significant worldwide energy source, with performance optimization studies such as these a necessary prerequisite.