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Tidal Turbine Theory
The performance graph below is a representation of the expected coefficients of performance that the test turbines will produce. The solid line represents the ideal Betz Limit. This is the limit created by the countering effects of Viscous losses (left side of graph) and Swirl losses (right side of graph). The smaller dashed line is the predicted curve that will be seen for one test turbine at the lead of a turbine array. The thicker dashed line represents the predicted performance of secondary turbines with opposite swirl effects. Secondary turbines could capture some of the lost efficiency in the primary turbines due to swirl.  The sketches below display the importance of a streamlined body on the turbine testing apparatus. Figure A shows a non-streamlined housing on the test apparatus. With this sort of shape there will be separation of the fluid boundary layer from the housing, increasing drag and having possible effects on the validity of data collected on the test turbine. Figure B shows a streamlined housing on the test apparatus. This sort of shape will significantly reduce separation of the fluid boundary layer, allowing for more accurate and reproducible readings on a test turbine.  As described above, the swirl effects of the turbine on the water are very significant in quantifying both the performance of individual turbines as well as arrays of turbines. The following two picture show a turbine test apparatus with the turbine before the supporting keel and with the turbine after the supporting keel. In the first situation, rotating flow leaving the turbine will not engage the supporting keel in a direct linear fashion. This will cause significant separation and drag effects. In the second situation, the linear flow hits the keel first, causing insignificant flow separation before the water engages the test turbine. Though a test apparatus with no supporting keel at all would be idea, the second situation is the most logical and effective design option available to the group.   Design Considerations Spreadsheet: Includes all considerations that should be made for a final, implementable, in ocean design. Feasibility, Adverse Effects, Physical Design |
Mechanical Engineering Senior Design 2007-2008
