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research-article

ON LES BASED CONJUGATE HEAT TRANSFER PROCEDURE FOR TRANSIENT NATURAL CONVECTION

[+] Author and Article Information
Mohamed Fadl

Department of Engineering Science, University of Oxford, Oxford OX1 3PJ, UK
moh_saker1981@yahoo.com

Li He

Department of Engineering Science, University of Oxford, Oxford OX1 3PJ, UK
li.he@eng.ox.ac.uk

1Corresponding author.

ASME doi:10.1115/1.4037492 History: Received July 12, 2017; Revised July 31, 2017

Abstract

Natural convection is an important heat transfer mode for flexible operations of gas turbines and steam turbines. Its prediction presents considerable challenges. The strong inter-dependence 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. 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 fluxes. A loosely coupled unsteady CHT procedure based on a multiscale methodology is subsequently developed. The multiscale framework provides an efficient way for accurately solving problems with huge time scale disparity. A particular emphasis of this work is on efficient and accurate transient CHT solutions in conjunction with the turbulence eddy resolved modelling (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 demonstrate the validity and effectiveness of the proposed methodology and implemented procedure.

Copyright (c) 2017 by ASME
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