Research Papers

Effect of Tip Clearance on the Prediction of Nonsynchronous Vibrations in Axial Compressors

[+] Author and Article Information
Martin Drolet

École Polytechnique de Montréal
and Pratt and Whitney Canada
1000 Boulevard Marie-Victorin
Longueuil, QC, J4G 1A1, Canada
e-mail: martin.drolet@polymtl.ca

Huu Duc Vo

e-mail: huu-duc.vo@polymtl.ca

Njuki W. Mureithi

e-mail: njuki.mureithi@polymtl.ca
École Polytechnique de Montréal
2500 chemin de Polytechnique
Montréal, QC, H3T 1J4, Canada

Contributed by the International Gas Turbine Institute (IGTI) for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 17, 2011; final manuscript received August 9, 2011; published online October 30, 2012. Editor: David Wisler.

J. Turbomach 135(1), 011023 (Oct 30, 2012) (10 pages) Paper No: TURBO-11-1140; doi: 10.1115/1.4006401 History: Received July 17, 2011; Revised August 09, 2011

This work investigates the effect of tip clearance size and operating temperature on the predictions of the critical rotor speed at which nonsynchronous vibrations (NSV) can be encountered in a turbine engine axial flow compressor. It has been proposed that the tangential tip clearance flow, observed at high blade loading near stall, can act as an impinging resonant jet on the upcoming blades and could be the underlying physics behind NSV. A model, in the form of an equation to predict the critical blade tip speed at which NSV can occur, was proposed based on the Jet-Core Feedback Theory and was experimentally verified by Thomassin et al. (2008, “Experimental Demonstration to the Tip Clearance Flow Resonance Behind Compressor NSV,” Proceedings of GT2008: ASME Turbo Expo Power for Land, Sea and Air, Berlin, Germany, Jun. 9–13, Paper No. GT2008-50303). In the equation, a factor k that was called the “tip instability convection coefficient” was measured experimentally and found to be influenced by the tip clearance size and operating temperature. This factor has a significant impact on the accuracy of the NSV predictions obtained using the proposed model. This paper propose a numerical experiment to determine the effect of tip clearance size and temperature on k, in order to improve the critical NSV tip speed predictions using the proposed model. A review of the NSV model is presented along with the relevant background theory on the subject. Two different blade geometries are simulated to provide a generic approach to the study. The leakage flow velocity is calculated to estimate k and a correlation is proposed to model the behavior of the k parameter as a function of the tip clearance size. The latter was found to significantly improve the critical NSV speed predictions. The effect of operating temperature on k is also discussed. Finally, the variation of k with the aerodynamic loading is assessed and compared with available data in the literature to strengthen the generic nature of the results.

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Fig. 1

Tip clearance flow impingement flow paths [8]

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Fig. 2

(a) The jet core feedback theory [3] and (b) physics of the proposed NSV model by Thomassin et al. [8]

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Fig. 3

NSV prediction on Campbell diagram

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Fig. 4

Measured instability convection coefficient k at different operating conditions, data from Ref. [8]

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Fig. 5

SR geometry: (a) side view (b) blade tip section

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Fig. 6

TR geometry: (a) side view (b) blade tip section

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Fig. 7

Typical chord-wise VL profiles calculated at different rotor speeds for (a) SR geometry at 1% chord tip clearance and (b) TR geometry at 0.4% chord tip clearance

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Fig. 8

Characteristics of the tip leakage flow: tip leakage velocity profiles for (a) SR geometry and (b) TR geometry, (c) area-averaged turbulent kinetic energy at tip averaged for all speed with logarithmic trend lines (dashed lines) and (d) anticipated trends in k with tip clearance based on velocity profiles behavior

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Fig. 9

Numerical results for calculated k, (a) overall results, and (b) comparison of available data in the literature with Eq. (11) fitted with speed-averaged numerical results

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Fig. 10

(a) Distorted velocity profiles calculated at 3.83% tip clearance for the subsonic geometry and (b) Ideal tip clearance flow model of Rains [13] as depicted in Ref. [12]

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Fig. 11

Calculated k at different inlet temperatures near stall for the TR geometry. Experimental data is from Ref. [8].

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Fig. 12

Calculated blade loading versus nondimensional tip clearance for both SR and TR geometries (data shown for all the different speeds)

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Fig. 13

(a) Equation (15) and its (b) derivative plotted versus ψ

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Fig. 14

Typical values of loading ψ and flow coefficient ϕ found near stall for most compressor geometries




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