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Research Papers: Gas Turbines: Structures and Dynamics

Enhanced Computational Fluid Dynamics Modeling and Laser Doppler Anemometer Measurements for the Air-Flow in an Aero-engine Front Bearing Chamber—Part II

[+] Author and Article Information
J. Aidarinis

Laboratory of Fluid Mechanics
and Turbomachinery,
Aristotle University of Thessaloniki,
Egnatia Street,
Thessaloniki 54124, Greece
e-mail: aidarini@auth.gr

A. Goulas

Laboratory of Fluid Mechanics
and Turbomachinery,
Aristotle University of Thessaloniki,
Egnatia Street,
Thessaloniki 54124, Greece
e-mail: goulas@auth.gr

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received August 20, 2014; final manuscript received November 13, 2014; published online January 28, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(8), 082502 (Aug 01, 2015) (15 pages) Paper No: GTP-14-1501; doi: 10.1115/1.4029365 History: Received August 20, 2014; Revised November 13, 2014; Online January 28, 2015

A detailed computational study of the air-flow through the outer gap of the front bearing of an aero-engine is presented. The reason to carry out this study was to understand the flow through the bearing as a function of the operational parameters of the engine, which was necessary for the modeling of the flow in the whole bearing chamber. The complex geometry and the size of the bearing gap relative to the overall dimensions of the bearing chamber and the need for very precise and detailed information of the effect on the flow within the chamber of the bearing operational parameters, prohibited the solution of the flow through the gap together with the rest of the bearing chamber. A 3D modeling of the flow through the outer bearing gap, which included a section of the ball bearing, was performed. Functions relating the pressure drop of the air coming through the bearing gap and the tangential component of velocity of the air exiting the bearing region, to the mass of air through the gap of the ball bearing and the rotational speed of the shaft were developed. The effect of the lubrication oil within the bearing was modeled as an anisotropic porous medium with a predefined law. In order to acquire in a mathematical form the above relationships a series of computational runs were performed. These relationships, in the form of second order curves, were subsequently introduced to the model of the bearing chamber as described by Aidarinis and Goulas (2014, “Enhanced CFD Modeling and LDA Measurements for the Air-Flow in an Aero Engine Front Bearing Chamber (Part I),” ASME Paper No. GT2014-26060). The constants of the relationships were derived through comparisons of the calculations with the experimental data. From the analysis, it was concluded that the pressure drop across the bearing increases with the square of the rotational speed of the shaft with the mass flow of air through the ball bearing as a parameter and vice versa. For this particular ball bearing, there is a region where, for any combination of rotational speed of the shaft and pressure drop through the bearing, there is no flow of air through the bearing. In this paper the detailed modeling methodology, the computational flow field, the boundary conditions and finally the results are presented and discussed.

Copyright © 2015 by ASME
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Figures

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Fig. 1

Front view of the bearing

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Fig. 4

Modeled outer bearing gap (21/21)

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Fig. 5

Modeled outer bearing gap shape (1/21)

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Fig. 6

Modeled bearing gap control surfaces (1/21)

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Fig. 7

3D CFD grid view (a), lower view (b), and side view (c)

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Fig. 8

3D computational domain and boundary conditions of the surfaces

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Fig. 9

Contours of axial air velocity UX (Uxi = 3.0 m/s): 5500 rpm, 7000 rpm, 4000 rpm, and 4000 rpm no porous media

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Fig. 10

Contours of circumferential air velocity Ut (Uxi = 3.0 m/s): 5500 rpm, 7000 rpm, 4000 rpm, and 4000 rpm no porous media

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Fig. 11

Contours of static pressure Pst (Uxi = 3.0 m/s): 5500 rpm, 7000 rpm, 4000 rpm, and 4000 rpm no porous media

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Fig. 12

Streamlines in the bearing gap region (Uxi = 3.0 m/s): 5500 rpm, 7000 rpm, 4000 rpm, and 4000 rpm no porous media

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Fig. 13

Ball bearing pressure loss versus axial inlet velocity as a function of porous media coefficients for 4000/5500 rpm

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Fig. 14

Ball bearing pressure loss versus bearing cage circumferential velocity as a function of porous media coefficients for Uxi = 3 m/s

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Fig. 15

Ball bearing circumferential exit velocity versus axial inlet velocity as a function of rotational speed for various porous media coefficients

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Fig. 16

The 3D surface of Eq. (6)

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Fig. 17

Axial velocity profiles for lines 22 and 24 (cases 2–4): air-flow 23 g/s, 4000 rpm; X = 163.5 mm and Y = 65 mm and air-flow 23 g/s, 4000 rpm; X = 163.5 mm and Y = 85 mm

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Fig. 18

Axial velocity contours at Y = 75 mm (cases 2–4): A1, A2, A3, and LDA

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Fig. 19

Axial velocity profiles for lines 11 and 24 (cases 2–5): air-flow 23 g/s, 5500 rpm; X = 143.5 mm and Y = 55 mm and air-flow 23 g/s, 5500 rpm; X = 163.5 mm and Y = 85 mm

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Fig. 20

Axial velocity contours at Y = 55 mm (cases 2–5): A2, A3, A4, and LDA

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Fig. 21

Axial velocity profiles for lines 11 and 14 (cases 2–7): air-flow 23 g/s, 7000 rpm; X = 143.5 mm and Y = 55 mm and air-flow 23 g/s, 7000 rpm; X = 143.5 mm and Y = 85 mm

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Fig. 22

Axial velocity contours at Y = 85 mm (cases 2–7): A5, BLK, A7, and LDA

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Fig. 23

Axial velocity profiles for lines 11 and 21 (cases 3 and 4): air-flow 33 g/s, 4000 rpm; X = 143.5 mm and Y = 55 mm and air-flow 33 g/s, 4000 rpm; X = 163.5 mm and Y = 55 mm

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Fig. 24

Axial velocity contours at Y = 65 mm (cases 3 and 4): A2, A3, A4, and LDA

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Fig. 25

Axial velocity profiles for lines 11 and 21 (cases 3–5): air-flow 33 g/s, 5500 rpm; X = 143.5 mm and Y = 55 mm and air-flow 33 g/s, 5500 rpm; X = 163.5 mm and Y = 55 mm

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Fig. 26

Axial velocity contours at Y = 85 mm (cases 3–5): A3, A4, A5, and LDA

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Fig. 28

Pressure loss across the modeled bearing versus shaft rotational speed as a function of axial inlet

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