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On the Effects of Unsteady Flow Conditions on the Performance of a Cross Flow Hydrokinetic Turbine

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Technical Report

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Hydrokinetic turbines convert the energy of flowing water into usable electricity. Axial flow and cross flow turbines are the most common forms of hydrokinetic turbine, however cross flow turbine performance and the impact of surface waves are not well understood. Test were conducted to observe the effects of waves on the performance characteristics of a cross flow turbine promulgated by the Department of Energys Reference Model Project, specifically Reference Model 2. Testing of a 16 scale model was conducted in the large towing tank in the Hydromechanics Laboratory. The scale model turbine had a 1.075 m diameter and blades with a height of 0.807 m and a NANA 0021 cross section. Baseline no wave turbine performance was compared to published data on the same model turbine. Additionally, test were conducted with incident waves, which were scaled to be large enough to create a shear in velocity across the span of the turbine. Tests were also conducted a various turbine depths and various tow speeds which resulted in a range of Reynolds numbers. The average turbine performance characteristics improved slightly as depth decreased due to acceleration of the constricted flow near the surface. Waves did no significantly change the performance of the turbine when averaged over of an entire cycle and several wave periods. This was the case even though the test waves created a velocity shear across the entire span of the blade. The waves were found to impart cyclic signatures in the torque measurement which may have consequences for instantaneous blade loading and power output from the device. A computational model was developed to predict turbine performance and compares favorably to the experiment at peak turbine performance. However, the model does not accurately predict the correct power at off peak conditions.

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  • Fluid Mechanics
  • Machinery and Tools

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