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Research Papers

On Large Eddy Simulation Based Conjugate Heat Transfer Procedure for Transient Natural Convection

[+] Author and Article Information
M. Fadl

Department of Engineering Science,
University of Oxford,
Oxford OX1 3PJ, UK
e-mail: m.s.fadl@lboro.ac.uk

L. He

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

1Present address: CREST, Loughborough University, Leicestershire LE11 3TU, UK.

2Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 12, 2017; final manuscript received July 31, 2017; published online September 6, 2017. Editor: Kenneth Hall.

J. Turbomach 139(11), 111010 (Sep 06, 2017) (9 pages) Paper No: TURBO-17-1086; doi: 10.1115/1.4037492 History: Received July 12, 2017; Revised July 31, 2017

Natural convection is an important heat transfer mode for flexible operations of gas turbines and steam turbines. Its prediction presents considerable challenges. The strong interdependence between fluid and solid parts points to the need for coupled fluid–solid conjugate heat transfer (CHT) methods. The fundamental fluid–solid time scale disparity is further compounded by the long-time scales of practical turbine flexible operations. In addition, if a high-fidelity flow model (e.g., large eddy simulation (LES)) is adopted to resolve turbulence fluctuations, extra mesh dependency on solid domain mesh may arise. In this work, understanding of the extra solid mesh dependency in a directly coupled LES based CHT procedure is gained by an interface response analysis, leading to a simple and clear characterization of erroneously predicted unsteady interface temperatures and heat fluxes. A loosely coupled unsteady CHT procedure based on a multiscale methodology for solving problems with large time scale disparity is subsequently developed. A particular emphasis of this work is on efficient and accurate transient CHT solutions in conjunction with the turbulence eddy resolved modeling (LES) for natural convection. A two-scale flow decomposition associated with a corresponding time-step split is adopted. The resultant triple-timing formation of the flow equations can be solved efficiently for the fluid–solid coupled system with disparate time scales. The problem statement, analysis, and the solution methods will be presented with case studies to underline the issues of interest and to demonstrate the validity and effectiveness of the proposed methodology and implemented procedure.

Copyright © 2017 by ASME
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References

Figures

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Fig. 1

Computational domain and mesh (CHT)

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Fig. 2

Time-mean (left) and instantaneous (right) velocity contours (range: 0–0.75 m/s) of LES solution (midaxial plane)

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Fig. 3

Time histories of wall heat flux for two fluid meshes (fluid-domain only LES)

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Fig. 4

Turbulence spectra for two different fluid meshes (fluid-domain only LES)

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Fig. 5

Turbulence velocity spectra for different meshes (fluid-domain only LES)

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Fig. 6

Interface temperatures for different meshes (steady RANS based CHT)

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Fig. 7

Interface heat fluxes for different meshes (steady RANS based CHT)

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Fig. 8

Interface temperatures for different meshes (directly coupled CHT using LES)

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Fig. 9

Interface heat fluxes for different meshes (directly coupled CHT using LES)

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Fig. 10

Time history of interface wall temperature for different meshes (directly coupled CHT using LES)

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Fig. 11

Temperature variations across fluid–solid interface (solid line: realistic; dash line: erroneous)

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Fig. 12

Interface temperatures for different meshes (loosely coupled CHT using LES)

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Fig. 13

Interface time-averaged heat flux for different meshes (loosely coupled CHT using LES)

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Fig. 14

Time-averaged heat fluxes for transient, 100 K/1 s (unsteady flow model versus quasi-steady flow model)

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Fig. 15

Time-averaged heat fluxes for transient, 100 K/30 s (unsteady flow model versus quasi-steady flow model)

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