16.1.3 Overview of the Problem Setup Procedure

For a single-mixture-fraction problem, you will perform the following steps:

1.   Choose the chemical description of the system: equilibrium, steady flamelet, unsteady flamelet, or diesel unsteady flamelet (Figure  16.1.1).

2.   Indicate whether the problem is adiabatic or non-adiabatic.

Figure 16.1.1: Defining Equilibrium Chemistry

3.   (steady laminar flamelet model only) Import a flamelet file or appropriate CHEMKIN mechanism file if generating flamelets (Figure  16.1.2).

Figure 16.1.2: Defining Steady Laminar Flamelet Chemistry

4.   Define the chemical boundary species to be considered for the streams in the reacting system model. Note that this step is not relevant in the case of flamelet import (Figure  16.1.3).

Figure 16.1.3: Defining Chemical Boundary Species

5.   (steady laminar flamelet model only) If you are generating flamelets, compute the flamelet state relationships of species mass fractions, density, and temperature as a function of mixture fraction and scalar dissipation (Figure  16.1.4).

Figure 16.1.4: Calculating Steady Flamelets

6.   Compute the final chemistry look-up table, containing mean values of species fractions, density, and temperature as a function of mean mixture fraction, mixture fraction variance, and possibly enthalpy and scalar dissipation. The contents of this look-up table will reflect your preceding inputs describing the turbulent reacting system (Figure  16.1.5).

Figure 16.1.5: Calculating the Chemistry Look-Up Table

The look-up table is the stored result of the integration of this equation (or this equation ) and this equation (in the separate Theory Guide). The look-up table will be used in ANSYS FLUENT to determine mean species mass fractions, density, and temperature from the values of mean mixture fraction ( $\overline{f}$), mixture fraction variance ( $\overline{f^{'2}}$), and possibly mean enthalpy ( $\overline{H}$) and mean scalar dissipation ( $\overline{\chi}$) as they are computed during the ANSYS FLUENT calculation of the reacting flow. See this section and this figure and this figure in the separate Theory Guide.

For a problem that includes a secondary stream (and, therefore, a second mixture fraction), you will perform the first two steps listed above for the single-mixture-fraction approach and then prepare a look-up table of instantaneous properties using this equation or this equation in the separate Theory Guide.