Lecture. - Belgique: Von Karman Instinute, 1999, 2001, 2003. 138 p.Foreword
Numerical simulation of flames is a growing field bringing important improvements to our under-standing of combustion. The main issues and related closures of turbulent combustion modeling are reviewed. Combustion problems involve strong coupling between chemistry, transport and fluid dynamics. The basic properties of laminar flames are first presented along with the major tools developed for modeling turbulent combustion. The links between the available closures are enlighted from a generic description of modeling tools. Then, examples of numerical models for mean burning rates are discussed for premixed turbulent combustion. The use of direct numerical simulation (UN'S) as a research instrument is illustrated for turbulent transport occurring in premixed combustion, gradient and counter-gradient modeling of turbulent fluxes is addressed. Finally, a review of the models for nonpremixed turbulent flames is given.Contents
Introduction
Balance equations
nstantaneous balance equations
Reynolds and Favre averaging
Favre averaged balance equations
Filtering and Large Eddy Simulation
Major properties of premixed, nonpremixed and partially premixed Flames
Laminar premixed flames
Laminar diffusion flames
Partially premixed flames
A direct analysis: Taylor’s expansion
Scales and diagrams for turbulent combustion
Introduction
Turbulent premixed combustion diagram
Introduction
Combustion regimes
Comments
Nonpremixed turbulent combustion diagram
Introduction
Tools for turbulent combustion modeling
Introduction
Scalar dissipation rate
Geometrical description
G-field equation
Flame surface density description
Flame wrinkling description
Statistical approaches: Probability density function
Introduction
Presumed probability density functions
Pdf balance equation
Joint velocity/concentrations pdf
Conditional Moment Closure (CMC)
Similarities and links between the tools
Reynolds-averaged models for turbulent premixed combustion
Turbulent flame speed
Eddy-Break-Up model
Bray-Moss-Libby (BML) model
Introduction
BML model analysis
Recovering mean reaction rate from tools relations
Reynolds and Favre averaging
Conditional averaging - Counter-gradient turbulent transport
Models based on the flame surface area estimation
Introduction
Algebraic expressions for the flame surface density SI
Flame surface density- balance equation closures
Analysis of the flame surface density balance equation
Flame stabilization modeling
A related approach: G-equation
S Turbulent transport in premixed combustion
Introduction
Direct numerical simulation analysis of turbulent transport
Introduction
Results
Physical analysis
External pressure gradient effects
Counter gradient transport - Experimental results
To include counter-gradient turbulent transport in modeling
Towards a conditional turbulence modeling ?
Reynolds averaged models for nonpremixed turbulent combustion
Introduction
Fuel/Air mixing modeling
Introduction
Balance equation and simple relaxation model for x
Models assuming infinitely fast chemistry
Eddy Dissipation Model
Presumed pdf: infinitely fast chemistry model (IFCM) .
Flamelet modeling
Introduction
Flame structure in composition space
Mixing modeling in SLFM
Conclusion
Flame surface density modeling, Coherent Flame Model (CFM)
MIL model
Conditional Moment Closure (CMC)
Pdf modeling
Turbulent micromixing
Linear relaxation model, IEM/LMSE
GIEM model
Stochastic micromixing closures
Interlinks PDF / Flame surface modeling
Joint velocity/concentrations pdf modeling
Large eddy simulation
Introduction
Unresolved turbulent fluxes modeling
Smagorinsky model
Scale similarity model
Germano dynamic model
Structure function models
Unresolved scalar transport
Simplest approaches for combustion modeling
Arrhenius law based on filtered quantities
Extension of algebraic Favre averaged approaches
Simple extension of the Germano dynamic model
LES models for non premixed combustion
Linear Eddy Model
Dynamic micro-mixing model
Probability Density functions
LES models for premixed combustion
Introduction
Artificially thickened flames
G-equation
Filtering the progress variable balance equation
Numerical costs
Conclusion
