title: A Universal Wall-Modeling Approach for Large-Eddy Simulations of Complex Turbulent Flows with Heat Transfer
Creators: name: Li, Yongxiang
Publisher: name: UNSPECIFIED
Year: 2023

description: Since last few decades, the Large-Eddy Simulation (LES) technique has been widely adapted from academic research to industrial practice with anticipation of LES to be accurate and reliable to predict the unsteady turbulent heat and fluid flows. However, in LES, fine numerical grids scaled by viscous length are indispensable to resolve the turbulent motions in the near-wall dominant flows, which makes LES of wall bounded flow very computational expensive and time-consuming. This shortcoming has limited and impeded the application of LES to realistic industrial flows with solid walls. To circumvent this problem, a widely applied method is to model the flow in the near-wall region, which is expected to provide the essential quantities accurately, e.g. the turbulent quantities in the outer layer, the frictional velocity and the heat flux in an energy system, with significantly reduced computational costs. Despite numerous available wall modeled LES (WMLES) approaches, they are rarely capable to predict the complex heat and fluid flows in a realistic industrial flow application, which is characterized as highly unsteady non-equilibrium wall bounded turbulent flow. The present work focuses on the development of a reliable and efficient universal wall-stress model for LES that allows to predict unsteady non-equilibrium wall bounded turbulent flows with conjugate heat transfer in industrial flow applications. It is progressively accomplished in four major steps: (1) the development of novel non-equilibrium wall functions for velocity and temperature in the context of turbulent and heated fluid flow; (2) implementation of the novel non-equilibrium wall functions into the framework of OpenFOAM by also taking into consideration of the conjugate heat transfer problem in the context of incompressible heat and fluid flow with constant and variable physical properties for LES; (3) verification and validation of the proposed WFLES approach by means of several generic benchmark test cases relevant to exhaust gas after-treatment systems. Thereby, the reference data-sets are complemented by in-house generated near-wall resolved LES, DNS data and experimental measurement; (4) application of the proposed WFLES to investigate the heat and fluid flow processes in an exhaust gas after-treatment system of a LADA Niva 21214 vehicle under typical driving condition. Thereby, the computed heat and fluid flow phenomena are compared with in-house experimental data. Important milestones are achieved in this work. In particular, a novel wall functions based wall-modeled LES method is developed as a numerical tool to predict complex turbulent flows with conjugate heat transfer in industrial flow applications. Which is first validated and verified using several typical industrial application relevant generic benchmark test cases, and then applied to predict the turbulent flow with conjugate heat transfer in an exhaust gas after-treatment system under a typical driving operating condition. The accuracy of the developed numerical tool is testified by the good agreement between numerical results and experimental measurement. This work demonstrates that the proposed wall functions based wall-modeled LES approach is a reliable and flexible numerical tool to predict accurately and economically the complex turbulent flows with conjugate heat transfer in realistic industrial flow applications.