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Handbook of Turbomachinery Second Edition Revised - Ventech!

Handbook of Turbomachinery Second Edition Revised - Ventech!

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Figure 38 Centrifugal stresses on a steam turbine blade airfoil.<br />

to a wide variation in actual stresses. This is discussed in more detail below,<br />

in the section on manufacturing and assembly stresses.<br />

High mean stresses, such as those induced by centrifugal loads, have a<br />

pronounced detrimental effect on the fatigue strength <strong>of</strong> high-strength<br />

materials such as blading alloys.<br />

Geometric Untwisting<br />

Centrifugal forces can induce untwisting <strong>of</strong> the blade. Such a shape change<br />

causes direct blade stresses, changes the blade’s natural frequency, and<br />

causes flow geometry distortion. This loading, and the next, centrifugal<br />

bending, affect longer blades <strong>of</strong> the LP turbine much more than blades in<br />

the HP or IP turbine.<br />

Copyright © 2003 Marcel Dekker, Inc.

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