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Pre-Stall Behavior of Several High-Speed Compressors FREE

[+] Author Affiliations
M. Tryfonidis, O. Etchevers, J. D. Paduano, A. H. Epstein

Massachusetts Institute of Technology, Cambridge, MA

G. J. Hendricks

United Technologies Research Center, East Hartford, CT

Paper No. 94-GT-387, pp. V001T01A135; 24 pages
doi:10.1115/94-GT-387
From:
  • ASME 1994 International Gas Turbine and Aeroengine Congress and Exposition
  • Volume 1: Turbomachinery
  • The Hague, Netherlands, June 13–16, 1994
  • Conference Sponsors: International Gas Turbine Institute
  • ISBN: 978-0-7918-7883-5
  • Copyright © 1994 by ASME

abstract

High speed compressor data immediately prior to rotating stall inception are analyzed and compared to stability theory. New techniques for the detection of small amplitude rotating waves in the presence of noise are detailed and experimental and signal processing pitfalls discussed. In all nine compressors examined, rotating stall precedes surge. Prior to rotating stall inception, all the machines support small-amplitude (<1% of fully developed stall) waves travelling about the circumference. Travelling wave strength and structure are shown to be a strong function of corrected speed. At low speeds, a −0.5 times shaft speed wave is present for hundreds of rotor revolutions prior to stall initiation. At 100% speed, a shaft speed rotating wave dominates, growing as stall initiation is approached (fully developed rotating stall occurs at about 1/2 of shaft speed). A new, 2-D, compressible hydrodynamic stability analysis is applied to the geometry of two of the compressors and gives results in agreement with data. The calculations show that, at low corrected speeds, these compressors behave predominantly as incompressible machines. The wave which first goes unstable is the 1/2 shaft frequency mode predicted by the incompressible Moore-Greitzer analysis and previously observed in low speed compressors. Compressibility becomes important at high corrected speeds and adds axial structure to the rotating waves. At 100% corrected speed, it is one of these hitherto unrecognized compressible modes which goes unstable first. The rotating frequency of this mode is constant and predicted to be approximately coincident with shaft speed at design. Thus, it is susceptible to excitation by geometric nonuniformities in the compressor. This new understanding of compressor dynamics is used to introduce the concept of travelling wave energy as a measure of compressor stability. Such a wave energy-based scheme is shown to consistently give an indication of low stability for significant periods (100–200 rotor revolutions) before stall initiation, even at 100% corrected speed.

Copyright © 1994 by ASME
Topics: Compressors
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