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Handbook of Turbomachinery Second Edition Revised - Ventech!

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Figure 48 Campbell diagram with limitations based on manufacturing and tuning<br />

requirements.<br />

below the seventh harmonic:<br />

H&<br />

60 40<br />

2<br />

1<br />

&7 ð14Þ<br />

1:5<br />

The frequency response <strong>of</strong> blades is typically verified as part <strong>of</strong> the<br />

manufacturing and quality-control process and compared to the permissible<br />

frequencies evaluated using a Campbell diagram. Then all other effects such<br />

as blade fixation and rotor-blade coupling are added to the frequency<br />

calculation and compared to the permissible frequency window.<br />

At higher modes, the frequencies are more difficult to calculate and<br />

test. Also, factors such as manufacturing tolerances, material properties,<br />

root attachment or disk effects, and the effects <strong>of</strong> deposits and/or erosion on<br />

the blade vane leading edge tend to cause the individual blade frequencies to<br />

scatter about the calculated frequency. Fortunately, at the higher harmonics<br />

the dynamic forces generated are usually lower.<br />

Copyright © 2003 Marcel Dekker, Inc.

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