Research Papers: Applications

Wavelet Analysis of Experimental Blade Vibrations During Interaction With an Abradable Coating

[+] Author and Article Information
Romain Mandard

EC Lille, LML,
Université Lille Nord de France,
CNRS, UMR 8107,
Villeneuve d'Ascq F-59650, France
e-mail: romain.mandard@centraliens-lille.org

Jean-François Witz

Université Lille Nord de France,
CNRS, UMR 8107,
Villeneuve d'Ascq F-59650, France

Yannick Desplanques

EC Lille, LML,
Université Lille Nord de France,
CNRS, UMR 8107,
Villeneuve d'Ascq F-59650, France

Jacky Fabis

The French Aerospace Lab,
Lille F-59000, France

Jean Meriaux

Site de Villaroche,
Moissy-Cramayel F-77550, France

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received June 17, 2013; final manuscript received April 11, 2014; published online May 6, 2014. Assoc. Editor: Mihai Arghir.

J. Tribol 136(3), 031102 (May 06, 2014) (13 pages) Paper No: TRIB-13-1124; doi: 10.1115/1.4027438 History: Received June 17, 2013; Revised April 11, 2014

Minimizing the clearance between turbofan blades and the surrounding casing is a key factor to achieving compressor efficiency. The deposition of an abradable coating on casings is one of the technologies used to reduce this blade-casing clearance and ensure blade integrity in the event of blade-casing contact. Aircraft in-service conditions may lead to interactions between the blade tip and the coated casing, during which wear of the abradable coating, blade dynamics, and interacting force are critical yet little-understood issues. In order to study blade/abradable-coating interactions of a few tens of milliseconds, experiments were conducted on a dedicated test rig. The experimental data were analyzed with the aim of determining the friction-induced vibrational modes of the blade. This involved a time-frequency analysis of the experimental blade strain using continuous wavelet transform (CWT) combined with a modal analysis of the blade. The latter was carried out with two kinds of kinematic boundary conditions at the blade tip: free and modified, by imposing contact with the abradable coating. The interaction data show that the blade vibration modes identified during interactions correspond to the free boundary condition due to the transitional nature of the phenomena and the very short duration of contacts. The properties of the continuous wavelet transform were then used to identify the occurrence of blade-coating contact. Two kinds of blade/abradable-coating interactions were identified: bouncing of the blade over short time periods associated with loss of abradable material and isolated contacts capable of amplifying the blade vibrations without causing significant wear of the abradable coating. The results obtained were corroborated by high-speed imaging of the interactions.

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Fig. 1

Schematic representation of blade/abradable-coating interaction: (a) actual compressor configuration and (b) reverse test-rig configuration

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Fig. 5

Raw signals obtained in experiment 3 (blade c)

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Fig. 4

Raw signals obtained in experiment 2 (blade b)

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Fig. 3

Raw signals obtained in experiment 1 (blade a)

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Fig. 2

(a) Side view and (b) top view of the incursion cell of the test rig

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Fig. 6

Experimental modal analysis of the incursion cell: meshing and directions of natural modes

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Fig. 7

Experimental set up for the modal analysis of the clamped-simply supported blade

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Fig. 8

Scales versus Fourier frequencies for the Morlet mother wavelet (p = 6)

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Fig. 9

Spectrogram representation of CWT: (a) blade strain εxx in experiment 2 (raw signal), (b) real part of CWT in scalogram representation, (c) scale and frequency distribution for scalogram B, (d) real part of CWT in spectrogram representation, and (e) scale and frequency distribution for scalogram D

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Fig. 12

Time-frequency decomposition of blade strain εxx in experiment 1

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Fig. 13

Time-frequency decomposition of blade strain εxx in experiment 2

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Fig. 14

Time-frequency decomposition of blade strain εxx in experiment 3

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Fig. 15

Time-frequency decomposition of the blade strain εxx in experiment 3 over the (7–21 ms) time window correlated with high-speed imaging

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Fig. 16

FFT spectrum of the blade strain εxx in experiment 1 over the (t1t2) time window

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Fig. 17

Dynamic blade-coating couplings for isolated contact

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Fig. 18

High-speed imaging of isolated blade-coating contact at time t5 in experiment 3

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Fig. 10

Comparison between STFT and CWT modulus for the time-frequency decomposition of the blade strain εxx in experiment 2: (a) raw signal, (b) STFT modulus, (c) CWT modulus, and (d) FFT modulus over the complete signal

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Fig. 11

Comparison between the real parts of STFT and CWT for the time-frequency decomposition of the blade strain εxx in experiment 2: (a) raw signal, (b) real part of STFT, (c) real part of CWT, and (d) FFT modulus over the complete signal



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