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Handbook of Turbomachinery Second Edition Revised - Ventech!

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with nonreflecting boundary conditions are still useful when compared with<br />

well-established analytic solutions (only available for single-row configurations)<br />

or specially designed single-row experimental tests for method<br />

validation purposes.<br />

Regarding the circumferential domain truncation, for both blade<br />

flutter and rotor–stator interaction problems, adjacent blades in one blade<br />

row would usually experience unsteadiness with a constant phase difference<br />

(interblade phase angle). Therefore, if a single-blade passage computation<br />

domain is taken (Fig. 18), a flow variable at the upper periodic boundary UU<br />

and that at the lower periodic boundary UL will have to satisfy the phaseshifted<br />

(or time-lagged) periodic condition:<br />

Where<br />

ULðx; tÞ ¼UUðx; t DtÞ ð30Þ<br />

Dtð¼ s=oÞ is the time lag <strong>of</strong> the flow variable at the lower boundary<br />

compared to that at the upper boundary.<br />

o is blade vibration (or blade passing) angular frequency.<br />

s is the interblade phase angle [Eqs. (6) and (7)].<br />

Figure 18 Single-passage computational domain with the phase-shifted periodicity<br />

(s ¼ interblade phase angle).<br />

Copyright © 2003 Marcel Dekker, Inc.

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