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Research Papers: Gas Turbines: Structures and Dynamics

A Computational Parametric Analysis of the Vibration of a Three-Spool Aero-Engine Under Multifrequency Unbalance Excitation

[+] Author and Article Information
Pham Minh Hai

School of Mechanical, Aerospace and Civil Engineering, University of Manchester, Manchester, M13 9PL, UKhai.pham@postgrad.manchester.ac.uk

Philip Bonello

School of Mechanical, Aerospace and Civil Engineering, University of Manchester, Manchester, M13 9PL, UKphilip.bonello@manchester.ac.uk

J. Eng. Gas Turbines Power 133(7), 072504 (Mar 22, 2011) (9 pages) doi:10.1115/1.4002664 History: Received May 11, 2010; Revised May 13, 2010; Published March 22, 2011; Online March 22, 2011

The integration of squeeze-film dampers (SFDs) in aero-engine assemblies is a highly cost-effective means of introducing damping in an otherwise lightly damped structure. However, their deployment requires careful unbalance response calculations that take due account of the SFDs’ nonlinearity, particularly when they are unsupported by a centralizing spring. Until recently, such calculations were prohibitive due to the large number of assembly modes that typically need to be considered. This problem has been overcome by the authors through the novel impulsive receptance method (IRM) and the receptance harmonic balance method (RHBM), which efficiently solve the nonlinear problem in the time and frequency domains, respectively. These methods have been illustrated on a realistic twin-spool engine and have been shown to be effective for both single frequency unbalance excitation (unbalance on a single rotor) and multifrequency unbalance (MFU) excitation (unbalance on both rotors). In the present paper, the methods are applied to a realistic three-spool engine and the aims are twofold: (i) to present some preliminary results of a parametric study into a three-spool aero-engine assembly and (ii) to propose a technique that makes use of both IRM and RHBM in producing the speed responses under MFU excitation (from all three rotors) with a realistic speed relation between the rotors. The latter technique is necessary since the speed ratio will vary along a realistic speed characteristic and the authors have previously solved the twin-spool MFU problem under a constant speed ratio condition. The approach used here is to approximate the speed characteristic by one in which the speed ratios are ratios of low integers, enabling the use of RHBM to finish off (to steady-state) time-transient solutions obtained through IRM. The parameter study shows that the application of simple bump-spring supports to selected, otherwise unsupported, SFDs along with slight sealing should have a beneficial effect on the dynamic response of aero-engines with heavy rotors.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic of a representative three-spool engine

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Figure 2

Point receptance frequency response at center of the housing of the SFD LP front in y-direction

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Figure 3

Axial distributions of weight (-◼-) and polar moment of inertia (-●-): locations of SFD bearings and unbalances

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Figure 4

Bump-spring support with adjustable preloading

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Figure 5

Variation of rotor speeds and speed ratios

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Figure 6

Frequency spectra of relative velocity in y-direction with magnitudes max-normalized: co-phased, unsealed, and no bump-springs

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Figure 7

Lifts of journal centers (normalized to the corresponding radial clearances): no bump-springs

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Figure 8

Half peak-to-peak displacement amplitudes taken at synchronous frequencies in y-direction (normalized to the corresponding radial clearances): co-phased, unsealed, and no bump-springs

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Figure 9

Half peak-to-peak displacement amplitudes taken at synchronous frequencies in y-direction (normalized to the corresponding radial clearances): co-phased, slightly sealed, and no bump-springs

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Figure 10

Half peak-to-peak displacement amplitudes taken at synchronous frequencies in y-direction (normalized to the corresponding radial clearances): antiphased, slightly sealed, and no bump-springs

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Figure 11

Lifts of journal centers (normalized to the corresponding radial clearances): co-phased and slightly sealed

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Figure 12

Half peak-to-peak displacement amplitudes taken at synchronous frequencies in y-direction (normalized to the corresponding radial clearances): co-phased, slightly sealed, and preloading 1

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Figure 13

Half peak-to-peak displacement amplitudes taken at synchronous frequencies in y-direction (normalized to the corresponding radial clearances): co-phased, slightly sealed, and preloading 2

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Figure 14

Approximated speeds with 5% rounded-off

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Figure 15

Half peak-to-peak displacement amplitudes taken at synchronous frequencies in y-direction (normalized to the corresponding radial clearances): co-phased, slightly sealed, preloading 2, and “approximated” speeds

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Figure 16

Comparison between RHBM (….) and IRM (—) orbits of SFD LP rear: approximated speeds

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Figure 17

Transverse and axial cross sections of SFD

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