Abstract
Cross-flow turbines are attractive for tidal energy conversion because of their ability to rotate regardless of the direction of the water inflow. One of the downfalls of these turbines, however, is that their blades operate under dynamic stall, which reduces lift, and therefore the power generation of the turbine. To optimize performance further, we are examining the effects of foil and trailing edge thickness on dynamic stall and the overall turbine performance.
Ocean Renewable Power Company (ORPC) developed a set of hydrofoils with a blunt trailing edge geometry. There are two base foil geometries, NACA 0018 and NACA 0024, which each have been adapted to have 0.4% and 4.0% trailing edge thickness as a percentage of chord length. These blades are made of a 3D printed ABS plastic over a rectangular steel core. The blades will be tested in the ORPC Model Reference cross-flow turbine. The ORPC Model Reference cross-flow turbine is a 1 meter diameter turbine with three blades and two support struts fixed at a separation distance of z/H =1, where z is the upper strut location in reference to the bottom strut and H is the overall blade length.
The ORPC Model Reference turbine with the new blades will then be tested using the UNH cross-flow turbine test bed. This is a low-drag, 2nd generation hydrokinetic turbine test bed, with a submerged frame made from extruded aluminum NACA 0020 struts, and can be used to test cross-flow turbines up to nominally 1 square meter cross-section. This allows turbine models to be of a size where performance becomes independent of Reynolds number while maintaining reasonable blockage. The test bed is then installed in the UNH Wave and Tow Tank. The UNH Tow and Wave Tank enables research where test bodies can be towed, subjected to wave action, or both. It is 12 ft wide, 8 ft deep, 120 ft long. A tow tank provides a clean uniform inflow, which is useful for turbine performance evaluation, wake measurements, and numerical model validation.
The objective of these experiments is to explore the effects of increased mean and trailing edge thickness. Tow tank testing will be repeated on all four blade sets and consist of a Reynolds number independence sweep to determine ideal tow speed for each blade, and performance testing to identify the peak coefficient of power at a consistent tip speed ratio for each turbine.