17.5 Postprocessing for Premixed Combustion Calculations

ANSYS FLUENT provides several additional reporting options for premixed combustion calculations. You can generate graphical plots or alphanumeric reports of the following items:

• Progress Variable

• Damkohler Number

• Stretch Factor

• Turbulent Flame Speed

• Static Temperature

• Product Formation Rate

• Laminar Flame Speed

• Critical Strain Rate

• Unburnt Fuel Mass Fraction

• Adiabatic Flame Temperature

These variables are contained in the Premixed Combustion... category of the variable selection drop-down list that appears in postprocessing dialog boxes. See Chapter  31 for a complete list of flow variables, field functions, and their definitions. Chapters  29 and 30 explain how to generate graphics displays and reports of data.

Note that Static Temperature and Adiabatic Flame Temperature will appear in the Premixed Combustion... category only for adiabatic premixed combustion calculations; for non-adiabatic calculations, Static Temperature will appear in the Temperature... category. Unburnt Fuel Mass Fraction will appear only for non-adiabatic models.

ANSYS FLUENT also provides several additional reporting options for premixed combustion calculations with the ECFM model for flame speed closure. You can generate graphical plots or alphanumeric reports of the same items that are available with the premixed mode, and in addition:

• Progress Variable Curvature

• Flame Area Density

• Net Flame Area Production

• Flame Area Production P1

• Flame Area Production P2

• Flame Area Production P3

• Intermittent Turb Net Flame Stretch

• Flame Area Destruction

These variables will also appear in the Premixed Combustion... category.

Computing Species Concentrations

If you know the composition of the unburnt and burnt mixtures in your model (i.e., if you have performed separate ANSYS FLUENT or external analyses of chemical equilibrium calculations or 1D premixed flames), you can compute the species concentrations in the domain using custom field functions:

• To determine the concentration of a species in the unburnt mixture, define the custom function $Y_u(1-c)$, where $Y_u$ is the mass fraction for the species in the unburnt mixture (specified by you) and $c$ is the value of the progress variable (computed by ANSYS FLUENT).

• To determine the concentration of a species in the burnt mixture, define the custom function $Y_b c$, where $Y_b$ is the mass fraction for the species in the burnt mixture (specified by you) and $c$ is the value of the progress variable (computed by ANSYS FLUENT).

See Section  31.5 for details about defining and using custom field functions.