Turbulent Flame Speed Closure (Complex Chemistry) Model Reference

Table 1. Turbulent Flame Speed Closure (Complex Chemistry) Model Reference
Theory	See Turbulent Flame Speed Closure.
Provided By	[physics continuum] > Models > Turbulence Chemistry Interactions
Example Node Path	Continua > Physics 1 > Models > Turbulent Flame Speed Closure (TFC)
Requires	Material: Multi-Component Gas Reaction Regime: Reacting Reacting Flow Models: Reacting Species Transport Reacting Species Transport Models: Complex Chemistry
Properties	Key properties are: Flame Speed Scaling Factor, Heat Release Rate Activation Threshold, and Flame Curvature Effect. See Turbulent Flame Speed Closure (Complex Chemistry) Model Properties.
Activates	Model Controls (child nodes)	Laminar Flame Speed and Turbulent Flame Speed
	Field Functions	Laminar Flame Speed, TFC Activity Indicator, Turbulent Flame Speed, Unburnt Thermal Diffusivity, and Wall Direction. See Field Functions.

Turbulent Flame Speed Closure (Complex Chemistry) Model Properties

Flame Speed Scaling Factor: A multiplier of the turbulent flame speed which allows you to increase the turbulent flame speed.
Heat Release Rate Activation Threshold: Only available when the Complex Chemistry > Approximation Options property Relax to Chemical Equilibrium is deactivated. Increasing this value (up to 1) selects fewer cells for flame propagation, which leads to more robust behaviour, however, flame positioning may become less accurate.
Flame Curvature Effect: Adds the contribution of the flame curvature to the turbulent flame speed. Usually this contribution is minor and tends to decrease the turbulent flame speed.
Enable Model before Start of Spark Time: Allows the TFC model to be activated before spark time.; The default is Off, meaning that only the underlying Complex Chemistry model (Laminar Flame Closure LFC) operates up to spark time.

Field Functions

Laminar Flame Speed: $s_{l}$ , defined by either Metghalchi Eqn. (3440) or Gulder Eqn. (3444).
TFC Activity Indicator: The volume in which the Turbulent Flame Speed Closure (TFC) model alters the chemical and diffusion terms to propagate the premixed flame front at the specified turbulent flame speed.
TFC Reaction Rate: The TFC reaction rate that is used in clustering is the target source from the TFC model for $Y_{c}$ , that is ${\dot{ω}}_{Y_{c}}^{t f c}$ in Eqn. (3435).
Turbulent Flame Speed: $s_{t}$ , defined by either Zimont Eqn. (3445) or Peters Eqn. (3450).
Unburnt Heat Release Rate: The heat that is released due to kinetic activity in the unburnt gases. This field function allows you to visualize areas in which the unburnt heat release rates are high—which indicates that knock is more likely to occur.
Unburnt Thermal Diffusivity: $α_{u}$ in Eqn. (3445).
Wall Direction

In addition to the above field functions, the following field functions are also available only when the Temporary Storage Retained property is activated for the Segregated Species solver.

Equivalence Ratio: Equivalence ratio $Φ$ in Eqn. (3443).
Exhaust Gas Recirculation Mass Fraction: Mass fraction of product (burnt) species $Y_{E G R}$ in Eqn. (3452).
Progress Variable: $c$ , in Eqn. (3535).
Species Correction Factor: $n_{f}$ calculated by Eqn. (3437).
Thermal Diffusion Flux Energy Source: $D$ in Eqn. (3434).
Unburnt Temperature: The conditional temperature in the unburnt gases. Allows you to construct the flame speed.

Laminar Flame Speed

Method	Corresponding Method Node
Gulder Laminar Flame Speed	Uses the Gülder laminar flame speed correlation Eqn. (3579). Activates the Gulder Laminar Flame Speed node which allows you to select a fuel using the Fuel Name property.
Metghalchi Laminar Flame Speed	Uses the Metghalchi laminar flame speed correlation Eqn. (3573). Activates the Metghalchi Laminar Flame Speed node which allows you to select a fuel using the Fuel Name property.
Precomputed LFS Table	Uses values taken from the Laminar Flame Speed Table that is specified under the Table Generators > LFS Table Generator node. Activates the Precomputed LFS Table node which allows you to select the Laminar Flame Speed Table defined in LFS Table Generator.
User Defined Laminar Flame Speed	Allows you to specify the unstrained laminar flame speed. Laminar Flame Speed > User Defined Laminar Flame Speed > Laminar Flame Speed Profile

Flame Speed Multiplier: Available for all Laminar Flame Speed (LFS) methods.; Allows you to multiply the LFS with a scale factor. The flame speed multiplier is applied to $S_{l}$ obtained from any of the LFS methods in Turbulent Flame Speed Closure.; Increasing the multiplier will increase the LFS and therefore the Turbulent Flame Speed. The recommended value ranges from 0.5 to 2. The default of 1 indicates that no multiplier is applied.

Turbulent Flame Speed

Method


Method	Corresponding Child Node
Peters Turbulent Flame Speed Selects the Peters method Eqn. (3450) for calculating the turbulent flame speed source term.	Peters Turbulent Flame Speed Properties: Wall Effect Constant Uses wall effects to model the quenching of the flame at walls. Select a setting from 0 (fully extinguished) to 1 (no effect). Constant, A1 Coefficient $A_{1}$ , from Eqn. (3451). Constant, A4 Coefficient $A_{4}$ , from Eqn. (3451). Constant, B1 Coefficient $B_{1}$ , from Eqn. (3451). Constant, B3 Coefficient $B_{3}$ , from Eqn. (3451). Ewald’s Corrector Constant $c_{e w}$ , from Eqn. (3451) Sub-nodes: Unburnt Thermal Diffusivity You can define the unburnt thermal diffusivity $D_{u}$ using the Power Law Eqn. (3486), or as a User-Defined Unburnt Thermal Diffusivity profile.
User Defined Turbulent Flame Speed Selects the User-Defined method for calculating the turbulent flame speed source term.	User Defined Turbulent Flame Speed Properties: Wall Effect Constant Uses wall effects to model the quenching of the flame at walls. Select a setting from 0 (fully extinguished) to 1 (no effect). Sub-nodes: Turbulent Flame Speed Profile Scalar profile value.
Zimont Turbulent Flame Speed Selects the Zimont method Eqn. (3445) for calculating the turbulent flame speed source term.	Zimont Turbulent Flame Speed Properties: Wall Effect Constant Uses wall effects to model the quenching of the flame at walls. Specify a setting from 0 (fully extinguished) to 1 (no effect). Flame Stretch Effect When activated, uses the flame stretch factor $G$ Eqn. (3446), which takes the flame stretch effect into account by representing the probability of unquenched flamelets. Activates the Flame Stretch Effect node. Sub-nodes: Unburnt Thermal Diffusivity You can define the unburnt thermal diffusivity using the Power Law or as a User-Defined Unburnt Thermal Diffusivity profile. Flame Stretch Effect Constant, ustr Coefficient $μ_{s t r}$ from Eqn. (3447). Critical Strain Rate Control Select either the Chemical Time Scale Methodwith which you can set the constant B in Eqn. (3449), or User Defined Profile