Performance of Bi-Directional Blades for Tidal Current Turbines

Horizontal-Axis Tidal Current Turbines can utilize bi-directional blades which operate well in both directions in a reversing flow, avoiding the use of yaw or pitch mechanisms, thus reducing initial and maintenance costs. A “class” of bi-directional hydrofoil shapes was designed, and studied numerically using OpenFOAM, and one foil with favorable characteristics, named B3-351045, was tested experimentally in the University of New Hampshire High-Speed Cavitation Tunnel - HiCaT. The foils were designed with considerations for lift, drag, and cavitation inception. Simplified 2D simulations for a range of angles of attack for foils with different foil-geometry parameters were used to select a favorable hydrofoil. The selected hydrofoil was fabricated and tested in the HiCaT. Lift and drag were measured using a custom-designed force balance and cavitation inception was observed visually. Experimental and numerical data were compared. Bi-directional blades may be an economically-feasible option when addressing the reversing direction of tidal flows, since the decreased performance of the blades can be offset by the lower costs compared to unidirectional blades.