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Handbook of Turbomachinery Second Edition Revised - Ventech!

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Figure 25 Variation <strong>of</strong> flow coefficient for various geometries <strong>of</strong> labyrinth seals.<br />

generation <strong>of</strong> seals, called brush seals, has been introduced and successfully<br />

applied to critical high-pressure gradient regions in many advanced gas<br />

turbines [100].<br />

Disc Plenum Buffering and Disc-Cooling Methods<br />

Although turbine airfoils are exposed to higher thermal loads, the turbine<br />

disc should be treated as the most critical component when failure is<br />

considered. Because disc alloys have temperature capabilities significantly<br />

lower than airfoil materials, cooling <strong>of</strong> the discs and prevention <strong>of</strong> the hot<br />

gas ingress into a disc cavity present a challenge for a design team. The flow<br />

in the disc cavity must also be understood so that proper cooling <strong>of</strong> the disc<br />

can be ensured in order to prevent thermal distress. Typical disc-cooling<br />

techniques can be based on<br />

Radial outflow <strong>of</strong> the cooling air (directly injected or preswirled) in the<br />

disc cavity between stator and rotor or between disc and corotating<br />

cover plate<br />

Jet impingement <strong>of</strong> the disc surface particularly at the critical disc rim<br />

location<br />

Cooling air leakages from the forward to aft cavity <strong>of</strong> the disc through<br />

small gaps in the blade-disc attachments<br />

Typically the cooling air source has a static pressure that is significantly<br />

higher than the static pressure in a disc cavity. This pressure differential can<br />

be utilized in a preswirling system to provide a tangential velocity<br />

Copyright © 2003 Marcel Dekker, Inc.

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