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Research Papers: Gas Turbines: Turbomachinery

Two-Phase Flow Pressure Drop in Corrugated Tubes Used in an Aero-engine Oil System

[+] Author and Article Information
Michael Flouros

MTU Aero Engines,
Munich 80995, Germany
e-mail: Michael.flouros@mtu.de

Andreas Kanarachos

Frederick Institute of Technology,
Nicosia 1036, Cyprus
e-mail: kanarachos.andreas@gmail.com

Kyros Yakinthos

Laboratory of Fluid Mechanics
and Turbomachinery,
AUTH,
Thessaloniki 54124, Greece
e-mail: kyak@auth.gr

Christina Salpingidou

Laboratory of Fluid Mechanics
and Turbomachinery,
AUTH,
Thessaloniki 54124, Greece
e-mail: csalpingidou@eng.auth.gr

Francois Cottier

MTU Aero Engines,
Munich 80995, Germany
e-mail: francois.cottier@mtu.de

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received August 26, 2015; final manuscript received September 4, 2015; published online November 17, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(6), 062603 (Nov 17, 2015) (22 pages) Paper No: GTP-15-1423; doi: 10.1115/1.4031627 History: Received August 26, 2015; Revised September 04, 2015

In modern aero-engines, the lubrication system holds a key role due to the demand for high reliability standards. An aero-engine bearing chamber contains components like bearings and gears. Oil is used for lubrication and for heat removal. In order to retain the oil in a bearing chamber, pressurized seals are used. These are pressurized using air from the compressor. In order to avoid overpressurization of the bearing chamber, air/oil passages are provided in the bearing chamber. At the top, a vent pipe discharges most of the sealing air and at the bottom, a scavenge pipe is used for discharging the oil by means of a pump (scavenge pump). The scavenge pipe is setup in most cases by tubes of circular or noncircular cross sections. When the scavenge pipe has to be routed in a way that sharp bends or elbows are unavoidable, flexible (corrugated) pipes can be used. Because of the corrugation, considerable flow resistance with high-pressure drop can result. This may cause overpressurization of the bearing compartment with oil loss into the turbomachinery with possibility of ignition, coking (carbon formation), or contamination of the aircraft’s air conditioning system. It is therefore important for the designer to be capable to predict the system’s pressure balance behavior. A real engine bearing chamber sealed by brush seals was used for generating different air/oil mixtures thus corresponding to different engine operating conditions. The mixtures were discharged through a scavenge pipe which was partly setup by corrugated tubes. Instead of a mechanical pump, an ejector was used for evacuating the bearing chamber. An extensive survey covering the existing technical literature on corrugated tube pressure drop was performed and is presented in this paper. The survey has covered both single-phase and multiphase flows. Existing methods were checked against the test results. The method which was most accurately predicting lean air test results from the rig was benchmarked and was used as the basis for extending into a two-phase flow pressure drop correlation by applying two-phase flow multiplier techniques similar to Lockhart and Martinelli. Comparisons of the new two-phase flow pressure drop correlation with an existing correlation by Shannak are presented for mixtures like air/oil, air/water, air/diesel, and air/kerosene. Finally, numerical analysis results using ansys cfx version 15 are presented.

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Figures

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Fig. 1

The test facility with the bearing chamber and the scavenge pipe

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Fig. 2

Different perspective for the corrugated tubes AB and BC

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Fig. 3

Typical sizes for PCA025. Outer diameter D2 = 33.9 mm, inner diameter D1 = 25.4 mm, pitch p = 5.2 mm, wall thickness t = 0.4 mm, and ridge depth r = 4.25 mm.

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Fig. 4

Bend loss coefficient CB for a 90 deg-bend

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Fig. 5

Comparison among results from different authors for a straight 10 m long corrugated pipe with medium water

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Fig. 6

Comparison among results from different authors for a straight 10 m long corrugated pipe with medium air

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Fig. 7

Comparison of experimental and predicted pressure drop by using Yeaple’s correlation

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Fig. 8

Comparison of experimental and predicted pressure drop by using Gropp’s correlation

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Fig. 9

High-speed camera shot of the scavenge flow showing the slug motion

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Fig. 10

Two-phase flow regimes according to Taitel and Dukler

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Fig. 11

Two-phase flow regimes according to Baker

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Fig. 12

Comparison of results for two-phase flow of air and oil between Shannak et al. and Flouros et al.

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Fig. 13

Comparison of results between correlations by Shannak et al. and Flouros et al. at a mass flux of 200 kg/m2 s and 5 bar inlet pressure

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Fig. 14

Comparison of results between correlations by Shannak et al. and Flouros et al. at a mass flux of 200 kg/m2 s and 10 bar inlet pressure

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Fig. 15

Comparison of results between correlations by Shannak et al. and Flouros et al. at a mass flux of 520 kg/m2 s and 5 bar inlet pressure

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Fig. 16

Comparison of results between correlations by Shannak et al. and Flouros et al. for air/oil mixture at 60 °C, a mass flux of 200 kg/m2 s, and at 5 bar inlet pressure

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Fig. 17

Comparison of between correlations by Shannak et al. and Flouros et al. at a mass flux of 200 kg/m2 s, 5 bar inlet pressure, and air/diesel mixture

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Fig. 18

Comparison of results between correlations by Shannak et al. and Flouros et al. at a mass flux of 200 kg/m2 s, 5 bar inlet pressure, and air/kerosene at 60 °C mixture

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Fig. 19

Comparison of computation results using the correlation of Flouros et al. for all four two-phase flow mixtures as a function of X

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Fig. 20

Comparison of computation results using the Shannak et al. correlation for all four two-phase flow mixtures as a function of X

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Fig. 21

Mixed dynamic viscosities according to Dukler for four mixtures as a function ofX

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Fig. 22

Comparison of experimental results for two-phase flow of air and oil with results derived by Friedel and Chisholm methods

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Fig. 23

Comparison of experimental results for two-phase flow of air and oil with results derived by Lockhart–Martinelli and homogeneous flow model

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Fig. 24

Comparison of computation results for two-phase flow of air and water with results derived by Friedel and Chisholm. At X = 1 (lean air), Gnielinski’s [39] pressure drop equations were used.

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Fig. 25

Comparison of computation results for two-phase flow of air and oil with results derived by Friedel and Chisholm

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Fig. 26

Comparison of computation results for two-phase flow of air and diesel with results derived by Friedel and Chisholm

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Fig. 27

Comparison of computation results for two-phase flow of air and kerosene with results derived by Friedel and Chisholm

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Fig. 28

Comparison of results for air and oil flow as a function of the mixing Re number using Friedel, Chisholm, and Flouros et al. methods. Remix calculation was based on Dukler’s homogeneous dynamic viscosity method.

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Fig. 29

Comparison of results for air and oil flow as a function of the mixing Re number using Friedel, Chisholm, and Flouros et al. methods. Remix calculation was based on Storek/Brauer homogeneous dynamic viscosity method.

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Fig. 30

Comparison of computation results using the Friedel (smooth pipe) correlation for four mixtures as a function of X

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Fig. 31

Comparison of computation results using the Chisholm (smooth pipe) correlation four mixtures as a function of X

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Fig. 32

Comparison of computation results using the Lockhart–Martinelli method for four mixtures as a function of X

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Fig. 33

Comparison of computation results using the homogeneous flow method for four mixtures as a function of X

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Fig. 34

Hexahedral mesh of the core stream and wall

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Fig. 35

The air velocity distribution into the tube. The flow is in the direction of the z-axis.

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Fig. 36

Recirculation zones within the corrugations (air flow)

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Fig. 37

Radial expansion s of the core stream (medium: air) into the corrugation

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Fig. 38

Radial expansion of the core stream as a function of the Re number for air at 40 °C

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Fig. 39

Comparison of single-phase flow results between CFD analysis and the Yeaple correlation for air, water, and oil

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