Date of Award

5-2012

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

Advisor

Michael L. Peterson

Second Committee Member

Richard W. Kimball

Third Committee Member

Gayle Zydlewski

Abstract

Hydro-kinetic tidal energy is a novel renewable resource with many potential sites located throughout the world. This thesis considers high solidity cross-flow turbines which are likely to be more fish friendly than axial flow turbines because they operate at low tip speed ratios while maintaining reasonable performance. At this time, limited experimental data exists that compares high solidity cross-flow turbine performance for different blade profiles. A cross-flow tidal turbine test bed was developed with power coefficient, thrust coefficient, and wake velocity measurement capabilities. Tow tank testing was performed for seven different blade profiles over a range of inflow velocities, tip speed ratios, and blade toe angles, with a constant blade number of four. Two-bladed tests were also performed for one of the profiles. Turbine rotational speed was controlled to eliminate the problem of turbine starting, allowing for testing at low tip speed ratios and conditions with negative power coefficients. Power coefficient results compared well with published data under similar test conditions; peak efficiencies were located at tip speed ratios consistent with modeling and had reasonable magnitudes that did not exceed the Betz limit.

A free vortex model was modified to include two effects: variation of blade toe angle, and a virtual incidence angle correction, which is an effect of flow curvature. These flow curvature effects were shown to be significant when the curvature index (blade chord length/turbine radius) was high, the case for the turbine geometries tested. Addition of the flow curvature correction significantly improved the comparison of the model with experimental data, specifically for the case of varying blade toe angle. These results are being used to validate the free vortex model, which can then be used to optimize the performance of cross-flow turbines.

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