Research Papers

The Tip Clearance Flow Resonance Behind Axial Compressor Nonsynchronous Vibration

[+] Author and Article Information
Jean Thomassin

 Pratt & Whitney Canada, 1000 Marie-Victorin, Longueuil, QC, J4G-1A1, Canada

Huu Duc Vo, Njuki W. Mureithi

 École Polytechnique de Montréal, 2500, Chemin de Polytehcnique, Montréal, QC, H3T-1J4, Canada

J. Turbomach 133(4), 041030 (Apr 27, 2011) (10 pages) doi:10.1115/1.4001368 History: Received February 13, 2009; Revised February 04, 2010; Published April 27, 2011; Online April 27, 2011

Nonsynchronous vibration (NSV) is a particular type of aero-elastic phenomenon, where the rotor blades vibrate at nonintegral multiples of the shaft rotational frequencies. NSV behavior appears similar to off-design stall flutter but with a particular blade tip flow evolution. This paper demonstrates the link between NSV and the resonance induced by the tip clearance flow based on a proposed hypothesis and experimental confirmation. At off-design operating conditions, the rotor blade tip clearance shear layer flow can evolve tangentially. It is proposed that this tangential flow becomes a support for an acoustic feedback wave that settles between rotor blades. The feedback wave is driven by the blade vibratory motion and synchronizes the shear layer vortical structures with the blade vibration frequency. Depending on the blade tip local temperature, and when the feedback wavelength matches within one or two blade pitches, the system becomes resonant and very high vibrations can occur on the blade. An axial stage compressor test rig is set-up to look into the underlying mechanism behind NSV through targeted measurements using both static and rotating instrumentation. The experimental apparatus consists of the first stage of a high pressure compressor driven by an electric motor. The test-section is built to minimize the effects of the adjacent stator blade rows in order to isolate the role of rotor blade tip clearance flow on NSV. Sensitivity studies are carried out to assess and demonstrate the effects of the rotor blade tip clearance and inlet temperature on NSV and validate the predicted resonance for NSV occurrence under various conditions. Vibrations and surface pressure data from adjacent blades are collected to demonstrate the predicted interactions between neighboring rotor blades. Finally, evidence of the staging phenomenon, inherent to the proposed NSV mechanism, is experimentally obtained. All the data obtained are consistent with and thus in support of the proposed mechanism for NSV.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 1

General features of oscillating shear layer (15)

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Figure 2

Oscillating shear layer impinging on a vibrating structure (14)

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Figure 3

Thomassin (14) NSV model summary

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Figure 4

NSV critical speed prediction

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Figure 5

Rotating rig test-section

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Figure 6

Installed compressor test rig

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Figure 7

Static instrumentation (casing)

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Figure 8

Rotating instrumentation

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Figure 9

NSV region and vibration amplification

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Figure 10

Normalized NSV vibration versus corrected speed

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Figure 11

Unsteady pressure correlation method

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Figure 12

Convection velocity UF

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Figure 13

Resonance condition

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Figure 14

Critical NSV speed prediction

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Figure 15

Influence of the feedback wave harmonic

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Figure 16

Maximum blade interactions




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