Efficiency of water turbinesGorlov and Darrieus are cross-axial type turbines, which unlike propellers, have shafts which rotate about an axis perpendicular to the flow. This makes them particularly suitable for the wide nozzle outlet aperture which is part of Manta Ray's design, as well as facilitating the coupling of multiple turbines on a common shaft. |
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Gorlov type turbines are a relatively recent recent innovation and are highly efficient. The main advantage of Darrieus turbines is that they are no longer covered by a patent (1931), but are afflicted by two problems:
Both of these could be overcome; the former by using a starter engine, which could be an integral part of the generator, while the latter would be improved by using multiple turbines operating out of phase.
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Axial flow turbines. |
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Cross-axial flow turbines. |
For further information please refer to
"Limits of the Turbine Efficiency
for Free Fluid Flow"
Alexander N. Gorban,
Alexander M. Gorlov,
Valentin M. Silantyev in
Journal of Energy Resources Technology
Vol. 123, Dec. 2001 pp. 312-7