On LES Based Conjugate Heat Transfer Procedure for Transient Natural Convection

Abstract

Natural convection prediction closely relevant to flexible operations (e.g. fast and frequent startups and showdowns) of gas turbines and steam turbines presents considerable challenges. The strong inter-dependence between fluid and solid parts points to the need for conjugate heat-transfer (CHT) methods. However, the long time scales of the practical operation processes of interest, and the fundamental fluid-solid time scale disparity raise general issues regarding the computational costs of the CHT methods. In particular, if a high-fidelity flow model (e.g. LES) needing to resolve smaller time scales of turbulence is adopted, we also face an additional question regarding the consistency and accuracy of the fluid-solid interface treatment. In this paper, we address the issues by the means of a loosely coupled CHT procedure based on the multi-scale methodology recently proposed for transient conjugate heat transfer predictions. The multi-scale framework provides an efficient way for accurately solving problems with a huge scale disparity. A particular emphasis of the present work is on efficient and accurate transient CHT solutions in conjunction with the turbulence eddy resolved modelling (LES) for natural convection. A multi-scale flow decomposition associated with the 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 very disparate time scales. The methodology will be presented with case studies supported by a new interface analysis to underpin the problem statement and motivation of the present work, and to demonstrate the validity and effectiveness of the methodology and implemented procedure.