Handbook of Turbomachinery Second Edition Revised - Ventech!

and/or clocking) effects than their stator–stator counterparts for transonic
compressors.
Aeroelastic Interaction (Blade Forced Response)
All the aforementioned interaction effects are of a pure aerodynamic nature
where the main concern is the corresponding time-averaged unsteady losses
resulting from the interactions, which are usually small. The blade
mechanical responses under those unsteady disturbances can have very
important consequences. Excessive stress levels at a blade resonant
condition, in which the frequency of an unsteady disturbance coincides
with that of a particular blade vibration mode, may occur due to lack of
damping (aerodynamic and/or mechanical). The frequencies of the blade
vibration modes at risk can be identified from the Campbell diagram (Fig.
6), when the frequency curves (e.g., those for the first flap ‘‘1F’’ and the first
torsion ‘‘1T’’) cross the engine order excitation lines (1EO, 2EO . . . ). Even if
the designer can choose an appropriate condition to avoid resonance at
design, it is difficult or impossible to do so at off-design conditions. When
the machine is started off or shut down, blades will have to go through some
resonance conditions, and it is important to be able to assess the unsteady
Figure 6 Campbell diagram.
Copyright © 2003 Marcel Dekker, Inc.