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Research Papers: Gas Turbines: Structures and Dynamics

Numerical and Experimental Investigations on Preload Effects in Air Foil Journal Bearings

[+] Author and Article Information
Marcel Mahner

Department of Mechanical Engineering,
Institute of Applied Dynamics,
Technical University of Darmstadt,
Otto-Berndt-Straße 2,
Darmstadt 64287, Germany
e-mail: mahner@ad.tu-darmstadt.de

Pu Li

Department of Mechanical Engineering,
Institute of Applied Dynamics,
Technical University of Darmstadt,
Otto-Berndt-Straße 2,
Darmstadt 64287, Germany
e-mail: li@ad.tu-darmstadt.de

Andreas Lehn

Department of Mechanical Engineering,
Institute of Applied Dynamics,
Technical University of Darmstadt,
Otto-Berndt-Straße 2,
Darmstadt 64287, Germany
e-mail: lehn@ad.tu-darmstadt.de

Bernhard Schweizer

Department of Mechanical Engineering,
Institute of Applied Dynamics,
Technical University of Darmstadt,
Otto-Berndt-Straße 2,
Darmstadt 64287, Germany
e-mail: schweizer@ad.tu-darmstadt.de

1Corresponding author.

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 19, 2017; final manuscript received July 25, 2017; published online October 17, 2017. Editor: David Wisler.

J. Eng. Gas Turbines Power 140(3), 032505 (Oct 17, 2017) (9 pages) Paper No: GTP-17-1376; doi: 10.1115/1.4037965 History: Received July 19, 2017; Revised July 25, 2017

A detailed elastogasdynamic model of a preloaded three-pad air foil journal bearing is presented. Bump and top foil deflections are herein calculated with a nonlinear beamshell theory according to Reissner. The two-dimensional pressure distribution in each bearing pad is described by the Reynolds equation for compressible fluids. The assembly preload is calculated by simulating the assembly process of top foil, bump foil, and shaft. Most advantageously, there is no need for the definition of an initial radial clearance in the presented model. With this model, the influence of the assembly preload on the static bearing hysteresis as well as on the aerodynamic bearing performance is investigated. For the purpose of model validation, the predicted hysteresis curves are compared with measured curves. The numerically predicted and the measured hysteresis curves show a good agreement. The numerical predictions exhibit that the assembly preload increases the elastic foil structural stiffness (in particular for moderate shaft displacements) and the bearing damping. It is observed that the effect of the fluid film on the overall bearing stiffness depends on the assembly preload: For lightly preloaded bearings, the fluid film affects the overall bearing stiffness considerably, while for heavily preloaded bearings the effect is rather small for a wide range of reaction forces. Furthermore, it is shown that the assembly preload increases the friction torque significantly.

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Figures

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Fig. 1

Preloaded three-pad air foil journal bearing with top andbump foils in initial configuration and in assembly configuration

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Fig. 2

Free body diagram of an infinitisimal beamshell segment [26]

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Fig. 3

Device for the automated measurement of air foil journal bearing hystereses

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Fig. 4

Direction of shaft displacement in the load-deflection test

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Fig. 5

Measured and predicted hysteresis curve of the lightly preloaded three-pad air foil journal bearing

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Fig. 6

Measured and predicted elastic foil structural stiffness of the lightly preloaded three-pad air foil journal bearing

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Fig. 7

Hysteresis curves for different assembly preloads of top and bump foil

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Fig. 8

Elastic foil structural stiffness for different assembly preloads of top and bump foil

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Fig. 9

Hysteresis curves with rotating and nonrotating shaft for different assembly preloads of top and bump foil

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Fig. 10

Overall bearing stiffness and elastic foil structural stiffness for the lightly preloaded bearing

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Fig. 11

Overall bearing stiffness and elastic foil structural stiffness for the heavily preloaded bearing

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Fig. 12

Friction torque on the shaft for different assembly preloads of top and bump foil

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