Analysis of a cycloidal wave energy converter using unsteady Reynolds averaged Navier-Stokes simulation

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University of New Brunswick
A computational fluid dynamic study was completed to investigate the two-dimensional wave generation and cancellation characteristics of the Atargis Cycloidal Wave Energy Converter (CycWEC). The numerical modeling was based on the unsteady Reynolds average Navier Stokes (URANS) equations and determined the free surface fluctuations using the volume of fluid method. A specialized hybrid grid design was required to accurately resolve the complex viscous flow field resulting from one or more hydrofoils rotating beneath the free surface at a constant angular velocity. The research progressed incrementally from single and two-hydrofoil wave generation concluded with two-hydrofoil wave cancellation. Unlike previous inviscid simulations, the URANS simulations were able to model nonlinear free surface interactions and viscous effects, allowing shaft torques to be numerically predicted for first time. It also provided complete velocity and pressure fields which previous experimental work could not. A grid refinement and time step sensitivity study are completed to increase simulation accuracy and computational efficiency. Fluctuations of wave height, surface pressure distribution, hydrodynamic force, and device efficiency from generated and cancelled wave fields are examined in detail for various hydrofoil pitch angles. For two-hydrofoil wave generation with large pitch angles URANS simulations predicted 94% of the required shaft power is transferred directly to the generated wave field. When operated as an energy extraction device the URANS simulations predicted that up to 92% of the incident wave field was cancelled and 82.7% of the average incident wave power was converted to useful shaft power.