Surface Wave Effects on Intracycle Blade Dynamics of Cross-Flow Turbines*

This project computationally investigates the effect of waves on marine energy cross-flow turbines (CFT) operating close to the water surface. CFTs extract energy from moving water with the axis of rotation perpendicular to the freestream velocity. Compared with the more common axial flow turbine, blade level dynamics of a CFT change throughout one cycle due to a transient airfoil orientation. These dynamics offer opportunities to optimize performance through control strategies and geometry changes. Previous research utilizes a steady uniform freestream velocity to understand CFT performance, but many turbines are installed in locations of non-uniform flow or close to a free surface. To understand these effects, a numerical model is developed for a turbine in uniform flow with surface wave conditions. The model uses the volume of fluid method to simulate and track the air-water interface. A two-bladed CFT is placed horizontally in the water channel. Simulations are conducted with and without the presence of waves under various operating conditions and wave parameters. Differences in conditions are investigated using flow field visualization. Turbine performance and unsteady forces on the blades are reported and results are compared with baseline turbine simulations. This framework is then used to characterize intracycle effects on dynamic stall and power production.