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Handbook of Turbomachinery Second Edition Revised - Ventech!

Handbook of Turbomachinery Second Edition Revised - Ventech!

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Features and Structure <strong>of</strong> LP Blades<br />

Figure 35 shows the nomenclature for arotating LP blade. Rotating LP<br />

turbine blades may be ‘‘free-standing,’’ that is, not connected to each other<br />

in any way; they may be connected in ‘‘groups’’ or ‘‘packets’’, each<br />

comprising several blades (generally between 2 and 8); or all blades in the<br />

whole row may be ‘‘continuously’’ connected. Free-standing blades have the<br />

following characteristics compared to grouped blades: (1) they have less<br />

inherent damping at the blade tips; (2) their resonances are more easily<br />

defined (i.e., no mechanical interactions with neighboring blades); (3) they<br />

have more aerodynamic interactions; and (4) they are easier to install and<br />

disassemble, as there are no welds or rivets [30, 31].<br />

In connected blades, there are a number <strong>of</strong> design choices. The<br />

connections may consist <strong>of</strong> shrouds (or bands) over the tips <strong>of</strong> the blades, or<br />

<strong>of</strong> tiewires (or lashing or lacing wires) located along the blade height as<br />

illustrated in Fig. 36. As with HP blades, connections made at the blade tip<br />

are termed shrouding. Shrouds may be inserted over tenons protruding<br />

above the blade tips, and these tenons then riveted down to secure the<br />

shrouds, or they may consist <strong>of</strong> integrally forged stubs in a welded or<br />

brazed-together assembly. Other types <strong>of</strong> riveted connections are also used.<br />

Tiewires may consist <strong>of</strong> either integrally forged stubs welded or brazed<br />

Figure 33 Steam turbine diaphragm construction.<br />

Copyright © 2003 Marcel Dekker, Inc.

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