Community Research and Development Information Service - CORDIS

The advantages of variable pitch air turbines

As fixed pitch self rectifying turbines can only be efficient for only a narrow range of airflows research was carried out on the design of variable pitch blades.

The following advantages of variable pitch were found:
higher air to shaft conversion efficiency was achieved at higher air flows (this could double the value of all preceding investment);
it is possible to choose whether to use smaller turbines which get into the efficient operating region at lower airflows;
overspeed protection without brakes can be provided;
a moderate amount of reactive loading can be applied to widen the frequency band of efficient operation giving perhaps 1.5 times the hydrodynamic productivity or to allow the use of smaller civil structures;
a minimum loading profile to ingested water can be presented.

If variable pitch is used with a low inertia variable speed link it is possible to:
maintain the proper damping coefficient over a wide range of flows;
use different damping coefficients for different wave spectra;
reduce idling drag losses during lulls;
apply larger amounts of reactive loading.

If variable pitch is used with hydraulics and energy storage it is possible to:
combine the outputs of adjacent turbines to further widen the usable sea state range;
run true synchronous generators at a steady mean rating with lower capital costs and less disturbance to slender island networks;
avoid conversion losses valued at the capital cost of a generator every year.

Reported by

University of Edinburgh
Kings Buildings Mayfield Road
EH9 3JL Edinburgh
United Kingdom
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