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Handbook of Turbomachinery Second Edition Revised - Ventech!

Handbook of Turbomachinery Second Edition Revised - Ventech!

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properly sizing the damper, a highly effective and relatively inexpensive<br />

design can be achieved for attenuating vibration levels. The correct sizing <strong>of</strong><br />

a fluid-film bearing is essential to proper system operation, and improper<br />

sizing may lead to serious problems. Additional information on the design<br />

<strong>of</strong> squeeze film dampers may be found in Vance [21].<br />

Solid Dampers<br />

There are a few alternatives to fluid-film dampers—<strong>of</strong>ten referred to solid<br />

dampers. One <strong>of</strong> these options is a device that operates in a manner similar<br />

to a fluid-film damper except the fluid is replaced by a solid elastomeric<br />

material. The viscoelastic properties <strong>of</strong> this material provide an energy<br />

dissipative effect that assists in attenuating the vibration levels in rotating<br />

machinery. These dampers possess the advantage <strong>of</strong> being simple in design,<br />

are relatively low in cost, and do not require a fluid with all the associated<br />

components required for fluid collection and recirculation. The main<br />

disadvantage, however, is that the damping forces generated by the solid<br />

damper are relatively low in comparison with those generated by fluid-film<br />

dampers. In addition, there are also temperature limitations to protect the<br />

elastomeric material from deterioration.<br />

Seals<br />

A seal is a mechanical component designed to minimize the flow <strong>of</strong> fluid<br />

(liquid or gas) from one region <strong>of</strong> a turbomachine to another. The goal <strong>of</strong> a<br />

design for such a device is to reduce the flow to zero and minimize the<br />

absorption <strong>of</strong> power and any tendency <strong>of</strong> the forces generated by the device<br />

to destabilize the transverse vibrational response <strong>of</strong> the rotating assembly.<br />

Numerous seal configurations have been developed over the years including<br />

designs referred to as floating contact, face, and labyrinth seals. The forces<br />

that exist between the rotating assembly and support structure for most<br />

seals are generally small and do not significantly affect the rotordynamic<br />

characteristics <strong>of</strong> the system. For certain configurations and operating<br />

conditions, however, the seal forces may be large enough to be considered in<br />

a rotordynamics performance evaluation. The seal in these situations serves<br />

not only as a seal to restrict axial-fluid flow, but also as a pseudo-bearing or<br />

damper. More detail concerning the properties <strong>of</strong> seals and their associated<br />

forces may be found in Childs [1].<br />

Working Fluid Mechanisms<br />

Fluid <strong>of</strong> some type (liquid, gas, steam) always flows through a turbomachine<br />

usually at high velocities and with complicated flow paths. Interaction forces<br />

Copyright © 2003 Marcel Dekker, Inc.

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