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Research Papers: Gas Turbines: Heat Transfer

Experimental Characterization of Rotor Convective Heat Transfer Coefficients in the Vicinity of a Leaf Seal

[+] Author and Article Information
Juan-Diego Pelegrin-Garcia

Department of Engineering Science,
University of Oxford,
Oxford OX1 3PJ, UK
e-mail: juan.pelegringarcia@eng.ox.ac.uk

David R. H. Gillespie

Department of Engineering Science,
University of Oxford,
Oxford OX1 3PJ, UK
e-mail: david.gillespie@eng.ox.ac.uk

Michael J. Pekris

Transmissions, Structures & Drives,
Rolls-Royce plc,
Derby DE24 8BJ, UK
e-mail: michael.pekris@rolls-royce.com

Gervas Franceschini

Transmissions, Structures & Drives,
Rolls-Royce plc,
Derby DE24 8BJ, UK
e-mail: gervas.franceschini@rolls-royce.com

Leonid Ganin

Department of Engineering Science,
University of Oxford,
Oxford OX1 3PJ, UK
e-mail: leonid.ganin@eng.ox.ac.uk

1Corresponding author.

Contributed by the Heat Transfer Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 28, 2016; final manuscript received July 19, 2016; published online September 27, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(3), 031901 (Sep 27, 2016) (10 pages) Paper No: GTP-16-1285; doi: 10.1115/1.4034519 History: Received June 28, 2016; Revised July 19, 2016

Leaf seals are filament seals for use at static to rotating interfaces in the engine secondary air system. They offer reduced leakage rates and better off-design performance over conventional labyrinth seals. If compared with advanced brush seals, leaf seals are more compliant due to their lower stiffness and can withstand higher axial pressure differences. Although leaf seals can exhibit hydrodynamic air-riding, this is not always the case and seal–rotor contact can occur. As a result, friction between the leaf tips and the rotor causes heat generation and wear. To predict the diameter of the rotating shaft and the seal life, the shaft and seal interface temperature needs to be estimated. In the steady state, this is determined by the ratio of convective heat transfer through the seal to that through the shaft. To that end, the convective heat transfer characteristics of the flow over the shaft around the seal are required to build accurate thermal models. In this paper, the convective heat transfer coefficient (HTC) distribution in the close vicinity of a typical leaf seal is investigated in a new test facility. The experimental setup and test method are described in detail, and accuracy considerations are included. The methodology employed to derive HTC is explained with reference to an analogous computational fluid dynamics (CFD) model. The importance of the choice of an appropriate driving gas temperature is demonstrated. Experimental HTC maps are presented for a blow-down seal geometry operating over a range of engine representative pressure ratios. Insight is gained into the flow field characteristics and heat transfer around the seal.

Copyright © 2016 by Rolls-Royce plc
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References

Figures

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Fig. 1

Leaf seal schematic [3]

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Fig. 2

Seal static thermal test facility (SSTTF)

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Fig. 3

Schematic of the test facility thermocouple instrumentation. The gas thermocouples are represented by the thick black lines on the diagram, and the position of the surface thermocouples and thermocouples embedded 1.5 mm below the surface by the circles in the lower part of the figure shows a part projected surface of the inner cylinder

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Fig. 4

Schematic of the heat flux sensor employed (not to scale)

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Fig. 5

Surface and gas temperature histories at the start of an unheated experiment, 2 bar seal pressure difference

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Fig. 6

Schematic of the data reduction methodology

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Fig. 7

CFD domain and boundary conditions

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Fig. 8

Computational mesh. The green region corresponds to the leaf pack porous zone.

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Fig. 9

Example of linear regression for CFD HTC calculation

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Fig. 10

Total and static temperature and velocity distributions downstream of the seal, case 3, q = 2500 W m−2, Tinlet = 323 K: (a) total temperature (K), (b) static temperature (K), and (c) velocity m s−1

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Fig. 11

Heat transfer coefficient derived set 1–3, Table 1, using linear regression: (a) HTC distribution and (b) normalized variation in reported HTC

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Fig. 12

Sealing performance of the seal

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Fig. 13

Gas temperature upstream (a) and downstream (b) of the seal (1 bar seal pressure difference)

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Fig. 14

Gas, surface, and embedded thermocouple temperature traces: (a) measurement location A1 (upstream side) and (b) measurement location B1 (downstream side)

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Fig. 15

Example of experimental strategy for measuring HTC: (a) heat flux measured during a typical test run and (b) typical regression fit

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Fig. 16

HTC variation with seal pressure difference: (a) HTC distribution upstream of the seal and (b) HTC distribution downstream of the seal

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Fig. 17

Comparison of experimental, CFD, and correlated HTC distributions at 1 bar seal differential pressure: (a) HTC distribution upstream of the seal and (b) HTC distribution downstream of the seal

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