Field Investigation of Bluff Body, Spring, Damping, and Mechanical Rectification Performance Impacts on a Galloping Current Energy Converter

Abstract The Water Horse is a galloping current energy converter, originally developed by Renerge Inc., which uses flow-induced oscillation to harness riverine hydrokinetic energy and convert it to electricity through a novel power takeoff (PTO) system. This article presents the correlational analysis of data collected during field testing of a Water Horse prototype at the University of Alaska Fairbanks (UAF) Tanana River Test Site in the summer of 2020. Testing focused on investigating the impacts of various system parameters on system level performance. Specifically, variations in bluff body sizing, spring stiffness, generator damping, and mechanical rectification of shaft rotation were correlated with oscillation frequency, oscillation amplitude, electrical output power, and water-to-wire efficiency. Completed at Reynolds numbers of 700,000 to 1,100,000, these data provide insight into galloping energy harvesting at the kW scale in a typical Alaska riverine environment. The bluff body with a smaller diameter and length delivered higher electrical power output than the larger bluff body; however, energy transfer into the floating platform was qualitatively higher with the larger bluff body. Removal of mechanical rectification led to increases in power production and system efficiency while decreasing peak-to-average power levels at the generator. The data show that optimal damping was not reached due to force limitations in the PTO design. Overall, total conversion efficiency was low, reaching a maximum total efficiency of 1.8% for the design swept area and a maximum specific efficiency of 2.6% for the actual swept area.