Handbook of Turbomachinery Second Edition Revised - Ventech!

Figure 14 Time-space static pressure contours on suction surface at 90% span
under different inlet distortion wavelengths.
while for the case with a long length scale [Fig. 14(b)] the moving shock
covers nearly 50% chord. Clearly, this long wavelength case with a large
shock oscillation is strongly nonlinear.
Given the importance of circumferential length scales, one should be
cautious about the practice of ‘‘slightly’’ changing blade counts to obtain a
much reduced multipassage computational domain—a drastic change in the
corresponding circumferential wavelength by doing so may result in a very
different unsteady response!
Phasing of Unsteady Disturbances
It must be kept in mind that influences of an unsteady disturbance depend
on its phase angle, not just the amplitude. The most obvious example is the
use of ‘‘antisound’’ where an acoustical noise disturbance can be completely
cancelled by artificially introducing an acoustical disturbance with the same
amplitude but a 1808 phase shift.
Phasing Between Wake and Potential Disturbances
In the context of blade forced responses, there is a scope of utilizing the
phase difference between wake and potential disturbances to produce
positive results. For example, a higher unsteady loading might not
Copyright © 2003 Marcel Dekker, Inc.