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Research Papers: Gas Turbines: Controls, Diagnostics, and Instrumentation

Ejector Scavenging of Bearing Chambers. A Numerical and Experimental Investigation

[+] Author and Article Information
Joachim Kutz

MTU Aero Engines,
80995 Munich, Germany

Agnes Jocher

Institute for Combustion Technology,
RWTH Aachen University,
52056 Aachen, Germany

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received March 1, 2013; final manuscript received March 7, 2013; published online June 24, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 135(8), 081602 (Jun 24, 2013) (7 pages) Paper No: GTP-13-1066; doi: 10.1115/1.4024259 History: Received March 01, 2013; Revised March 07, 2013

Oil system architecture in aero engines has remained almost the same for the last 30 years. At least one oil feed pump is responsible for distributing pressurized oil into the bearing chambers, and several scavenge pumps are responsible for evacuating the bearing chambers from the oil and the air mixture. Air is used as the sealing medium in bearing chambers and is the dominant medium in terms of volume occupation and expansion phenomena. In order to simplify the oil system architecture and thus improve the system's reliability with less mechanical parts and also decrease weight, an ejector system has been designed for scavenging bearing chambers. The idea behind the ejector is to use high-pressure oil from the feed pump and use it for feeding the ejector's primary jet. Through the momentum transfer between the pressurized oil at the jet's tip and the two-phase mixture of air and oil from the bearing chamber, the mixture will be discharged into the oil tank. In order to design the ejector for aero engine applications, engine-relevant performance conditions had to be considered. The design was performed using a one-dimensional analysis tool and then considerably refined by using the numerical tool ansys cfx. In a further step, the ejector was manufactured out of pure quartz glass and was tested in a lube rig with a bearing chamber, which has evolved from a real engine application. In the bearing chamber, engine-relevant performance conditions were simulated. Through the provided instrumentation for pressures, temperatures, and air/oil flows, the performance characteristics of the ejector were assessed and were compared to the analytic and numerical results. A high-speed camera was used to record the two-phase flow downstream of the bearing chamber in the scavenge pipe. This work is part of the European Union-funded research program Engine LUBrication System TechnologieS (ELUBSYS) within the 7th EU Frame Programme for Aeronautics and Transport (AAT.2008.4.2.3).

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References

ESDU, 1985, “Ejectors and Jet Pumps—Design and Performance for Incompressible Liquid Flows,” Paper No. ESDU 85032.
Jocher, A., 2011, “Auslegung und Fluidmechanische Untersuchung eines Zweiphasen-Ejektors fuer Flugtriebwerke (Design and Fluid Mechanical Investigation of a Two-Phase Flow Ejector for Aero-Engines),” Master's thesis, Munich Technical University, Munich, Germany.
Levy, S., 1999, Two Phase Flow in Complex Systems, Wiley & Sons, New York, pp. 90–107.
Storek, H., and Brauer, H., 1980, “Reibungsdruckverlust der Adiabaten Gas/Fluessigkeitstroemung in Horizontalen und Vertikalen Rohren (Frictional Pressure Loss of the Adiabatic Gas/Liquid Flow in Horizontal and Vertical Pipes),” VDI Forschungsheft, Vol. 599, VDI, Verlag, pp. 8–9.
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Ishii, M., and Zuber, N., 1979, “Drag Coefficient and Relative Velocity in Bubbly, Droplet or Particulate Flows,” AIChE J., 25(5), pp. 843–855. [CrossRef]
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Figures

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Fig. 1

Bearing chamber using ejector scavenging. High-speed cams were used to visualize the flow at different sections.

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Fig. 2

The MTU rig facility

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Fig. 3

The bearing chamber

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Fig. 4

Ejector characteristics

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Fig. 5

Selected ejector configuration

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Fig. 6

The computed ejector with its relevant dimensions

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Fig. 7

The flow pattern in the ejector at 1 g/s air and 450 L/H oil as secondary flow. The primary flow is 260 L/H. The dark areas are pure oil; the brighter areas indicate air entrainment.

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Fig. 8

High-speed snapshot of the scavenge flow

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Fig. 9

Picture of quartz glass ejector. The primary nozzle was axially adjustable.

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Fig. 10

The ejector arrangement in the rig setup

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Fig. 11

Different sprayers were used in the ejector for the primary flow

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Fig. 12

The performance curves of the ejector for two primary nozzle positions as a function of the secondary flow

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Fig. 13

Proper function of the ejector, even at 60 deg nose up

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Fig. 14

At a very low bearing chamber pressure (<0.1 barg), the ejector gets choked

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Fig. 15

The ejector at horizontal position at an air flow of 1 g/s, 450 L/H secondary oil, and 260 L/H primary oil flow

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