November 19, 2009
Wave turbine takes wing
the blades of a paddle-wheel-style wave turbine like airplane wings
and you can boost the amount of electricity that can be extracted
from the ocean.
Previous paddle wheel, or cycloidal, turbines work by drag
-- the flow of water pushing against the blades -- or by a combination
of drag and lift. A new turbine, designed by U.S. Air Force Academy
aeronautical engineers, works by lift alone, which is more efficient.
Drag produces more turbulence, which reduces the amount of energy
transferred from waves.
Lift is the way airplane wings and helicopter blades work;
a specially-shaped blade produces a perpendicular force (up in the
case of aircraft) by reducing the pressure on one side of the blade
when it moves edge-wise through air or water.
The turbine is designed to work in the open ocean where wave
energy is strongest. The turbine can remain in place without mooring
because a cluster of lifting blades can be angled to cancel the wave
energy. Mooring is difficult and expensive in the deep ocean.
Computer models and small-scale prototypes show that under
optimal conditions the turbine would convert 97 percent of wave energy
to power that turns a generator shaft. Other high-efficiency wave
energy devices are limited to low-wave shallow waters.
A lift-based cycloidal turbine in the North Atlantic, where
wave energy is about twice the global average, would be able to transfer
up to 100 kilowatts of power per meter of wave crest to a generator.
Assuming a generator efficiency of 90 percent, a turbine spanning
40 meters would produce about 3.6 megawatts of electricity, which
is the same as a 120-meter-diameter state-of-the-art offshore wind
Ocean Wave Cancellation Using a Cycloidal Turbine
62nd Annual Meeting of the APS Division of Fluid Dynamics, Minneapolis,
November 24, 2009
press release -- see Stefan Siegel's contact information
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