Research Papers: Flows in Complex Systems

Pre-Stall Instability Distribution Over a Transonic Compressor Rotor

[+] Author and Article Information
A. J. Gannon, G. V. Hobson

Turbopropulsion Laboratory, Naval Postgraduate School, Monterey, CA 93943

J. Fluids Eng 131(5), 051106 (Apr 23, 2009) (11 pages) doi:10.1115/1.3112388 History: Received August 18, 2008; Revised January 29, 2009; Published April 23, 2009

An investigation of the behavior of a transonic compressor rotor when operating close to stall is presented. The specific areas of interest are the behavior and location of low-frequency instabilities close to stall. In running close to stall, compressors can begin to exhibit nonperiodic flow between the blade passages even when appearing to be operating in a stable steady-state condition. The data from the current rotor clearly show that low-frequency instabilities were present during steady-state operation when stall was approached. These frequencies are not geometrically fixed to the rotor and typically appear at 0.3–0.8 of the rotor speed. The presence of these low-frequency instabilities is known and detection is reasonably commonplace; however, attempts to quantify the location and strength of these instabilities as stall is approached have proved difficult. In the current test fast response pressure sensors were positioned in the case-wall; upstream, downstream, and over the rotor blade tips. Simultaneous data from the sensors were taken at successive steady-state settings with each being closer to stall. A time domain analysis of the data investigates the magnitude of the instabilities and their transient effect on the relative inlet flow angle. The data are also presented in the frequency domain to show the development and distribution of the instabilities over the rotor as stall was approached. Initially the instabilities appeared within the rotor row and extended downstream but at operation closer to stall they began to protrude upstream as well. The greatest amplitude of the instabilities was within the blade row in the complex flow region that contains phenomena such as the tip-vortex/normal-shock interaction and the shock/boundary-layer interaction. In addition as stall is approached the growth of the instabilities is nonlinear and not confined to one frequency.

Copyright © 2009 by American Society of Mechanical Engineers
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Figure 1

Transonic test rotor

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Figure 2

Transonic test rotor

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Figure 3

Kulite sensor positions

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Figure 4

Rotor-only performance maps

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Figure 5

Experimental pressure contours near stall, 95% speed (A)

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Figure 6

Resultant filtered signal (95%)

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Figure 7

Filtered signals through the rotor (95%)

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Figure 8

Relative inlet angle variation close to stall

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Figure 9

Spectral analysis from FFT (log-log scale)

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Figure 10

Low-frequency region (linear scale)

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Figure 11

Near-stall low-frequency instabilities (95%)

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Figure 12

Far from stall low frequencies (95%)

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Figure 13

Near-stall low-frequency instabilities (90%)

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Figure 14

Near-stall low-frequency instabilities (70%)




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