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Research Papers

Parker-Type Acoustic Resonances in the Return Guide Vane Cascade of a Centrifugal Compressor – Theoretical Modeling and Experimental Verification

[+] Author and Article Information
Sven König

 Energy Sector Oil and Gas Division, Process Compression, Siemens AG, Duisburg, 47053, Germanykoenig.sven@siemens.com

Nico Petry

 Institute of Energy and Environmental Engineering, Turbomachinery Division, Duisburg, 47048, Germanynico.petry@siemens.com

Due to the symmetry conditions of the Parker modes—as discussed earlier in the paper—the instrumentation of only one vane passage is sufficient for this study.

In reality the speed of sound increases with rotor speed. Since no temperature measurements are available within the RGV, the assumption of a constant speed of sound gives the best approximation for the nonequilibrium conditions during each run-up.

This is due to the approximation of the calculated frequencies as horizontal straight lines (assumption of constant speed of sound for the depicted speed range)

This aspect will be discussed in detail in the next subsection.

J. Turbomach 134(6), 061029 (Sep 12, 2012) (10 pages) doi:10.1115/1.4006316 History: Received October 26, 2010; Revised December 15, 2010; Published September 12, 2012; Online September 12, 2012

The potential of acoustic resonances within vane arrays of turbomachinery has been known since the fundamental investigations of Parker back in the sixties and seventies. In his basic studies on flat plate arrays (and later on for an axial compressor) he could show that vortex shedding from the respective trailing edges may excite acoustic resonances that are localized to the vaned flow region. In principle, such phenomena are conceivable for any kind of turbomachinery; however, no such investigations are publicly available for the centrifugal type. The current investigation is one part of an extended research program to gain a better understanding of excitation and noise generating mechanism in centrifugal compressors, and focuses on Parker-type acoustic resonances within the return guide vane cascade of a high-pressure centrifugal compressor. A simplified model to calculate the respective acoustic eigenfrequencies is presented, and the results are compared with finite element analyses. Furthermore, the calculated mode shapes and frequencies are compared with experimental results. It is shown that for high-pressure centrifugal compressors, according to the nomenclature of Parker, acoustic modes of the α, β, γ, and δ type exist over a wide operating range within the return guide vane cascade. For engine representative Reynolds numbers, the experimental results indicate that the vortex shedding frequencies from the vane trailing edges cannot be characterized by a definite Strouhal number; the excitation of the Parker-type acoustic modes is mostly broadband due to the flow turbulence. No lock-in phenomenon between vortex shedding and acoustic modes takes place, and the amplitudes of the acoustic resonances are too small to cause machines failures or excessive noise levels. The simplified model presented in the current paper has been successfully validated for the return guide vane cascade of a centrifugal compressor but can also be applied for arbitrary blade and vane arrays, given that the chord-to-pitch ratio is sufficiently high. With this model, frequency components in measured pressure signals, that were left unexplained in the past, can be easily inspected for possible Parker-type resonances.

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Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Experimental arrangement of Parker [7]

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Figure 2

Amplitude contours for α mode, C/s = 1.55, whole wind tunnel

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Figure 3

Amplitude contours for different acoustics modes, C/s = 1.55

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Figure 4

Frequency curves for varying chord-to-pitch ratios

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Figure 5

Reference case for α and β mode

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Figure 6

Reference case for γ and δ mode

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Figure 7

Computational mesh for return guide vane cascade

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Figure 8

Acoustics modes in return guide vane cascade

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Figure 9

Illustration of different compressor run-ups

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Figure 10

(a): Run-up close to choke line, sensor S2; (b): Run-up close to choke line, sensor S1; (c): Run-up through design point, sensor S2

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