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Research Papers: Gas Turbines: Structures and Dynamics

On Nonlinear Rotor Dynamic Effects of Aerodynamic Bearings With Simple Flexible Rotors

[+] Author and Article Information
B. Bou-Saïd1

 Laboratoire de Mécanique des Contacts et des Solides, Bâtiment Jean D’Alembert 20 Rue des Sciences INSA, 20 Avenue A. Einstein 69 621, Villeurbanne Cedex, Francebenyebka.bou-said@insa-lyon.fr

G. Grau

 Microturbo 8 Chemin du Pont de Rupé BP 2089, Toulouse Cedex 2, 31 019 France

I. Iordanoff

 ENSAM-33405, Talence Cedex, France

1

Corresponding author.

J. Eng. Gas Turbines Power 130(1), 012503 (Dec 26, 2007) (9 pages) doi:10.1115/1.2747262 History: Received July 07, 2006; Revised March 27, 2007; Published December 26, 2007

The last decades have experienced a growing enhancement of aeronautical oil free turbomachinery. The classical linear approach of rotor dynamics commonly uses stiffness and damping coefficients to model journal bearings. In the present study, a nonlinear time dependant calculation is used for the dynamic simulation of a rotor mounted with aerodynamic (gas) bearings. A comparison between the two approaches indicates that the dynamic behavior of such bearings can be nonlinear in operating ranges where the rotor eccentricity reaches high values. In that case, the linear approach may lead to incorrect results and the nonlinear approach should be performed for better rotor dynamic prediction. A numerical procedure which analyzes the dynamic behavior of simple flexible rotors taking into account the nonlinear (transient regime) characteristics of aerodynamic bearings is presented. A simple example highlights the needs of nonlinear simulations in order to predict dynamic performance in oil-free turbomachinery.

Copyright © 2008 by American Society of Mechanical Engineers
Topics: Bearings , Damping , Rotors
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References

Figures

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Figure 1

Bump foil bearing description

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Figure 2

Evolution of critical speed value against the dimensionless static load

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Figure 3

Comparison of linear and nonlinear approaches

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Figure 4

Sketch of the model

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Figure 5

Schematic of three lobed deformable bearing

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Figure 6

Critical engine failure speed diagram for various values of α

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Figure 7

Schematic representation of the considered vibration modes

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Figure 8

Coordinate representation

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Figure 9

Stiffness and damping coefficients of a ball bearing

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Figure 10

Configuration of the reference case

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Figure 11

Dynamic response at y=l2

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Figure 12

Scematic of a hollow shaft with a central disk

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Figure 13

Comparison between the Rayleigh-Ritz model and rigid rotor model

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Figure 14

Response curve to unbalance. Comparison with the rigid case.

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Figure 15

Deformation of the rotor at 4000rpm

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Figure 16

Deformation of the rotor at 9600rpm

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Figure 17

Response curves to unbalance in configuration ball bearings, air bearings with linear and nonlinear action

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