Towards large eddy simulation of dispersed gas-liquid two-phase turbulent flows.

摘要

This study presents a detailed investigation of all essential components of computational and modeling issues necessary for a successful large-eddy simulation (LES) of dispersed two-phase turbulent flows. In particular, a two-layer concept is proposed to enable the LES capability in two-phase flows involving dispersed bubbles that are relatively large compared to the mesh size. The work comprises three major parts.; Part I focuses on the development and verification of a transient, three-dimensional, finite-volume-method (FVM) based accurate Navier-Stokes solver, named DREAM II (second generation of the DREAM code). Several high-order schemes are implemented for both the spatial and temporal discretization. Solution of the coupled partial differential equations is attacked with a fractional step (projection) method. The developed solver is verified against various benchmarks including Taylor's vortex, free-shear layer, backward-facing step flow and square cavity. A second-order overall accuracy is achieved in both space and time.; Part II concerns the modeling and LES of single-phase turbulent flows. A review of the LES theory and subgrid-scale (SGS) models is presented. Three SGS models, namely, Smagorinsky model, dynamic model and implicit model, are implemented and investigated. Then turbulent channel flow, plane mixing layer, and flow past a square cylinder are simulated, and comparisons of the first-, second-order statistics, and characteristic flow structures are made with direct numerical simulation (DNS) and/or benchmark experiments. The test results show superior quality of the present LES.; Part III delves into the theory, modeling and simulation of dispersed two-phase flow systems. A conceptual review of the characteristics and description of such system is made, considering both Eulerian-Eulerian (E-E) and Eulerian-Lagrangian (E-L) approaches, but with an emphasis on the latter. Various hydrodynamic forces acting on particles or bubbles are summarized and interpreted. Formulations regarding interphase coupling is discussed in depth. Typical computational treatments of modeled two-way couplings in an E-L DNS/LES are reviewed. Issues related to the interpolation are addressed. A general Lagrangian particle-tracking (LPT) program, named PART, is developed and verified using analytical solutions. (Abstract shortened by UMI.)