Turbulent Flame Speed Closure (Flamelet) Model Reference

• Zimont, the most widely used option for constant pressure combustion simulations
• Peters, commonly for internal combustion engines
• User Defined, a scalar profile

Turbulent Flame Speed Closure (Flamelet) Model Properties

Convection

Sets the discretization scheme that Simcenter STAR-CCM+ uses for computing the convection flux on a cell face in appropriate transport equations. More information is given in the related topic for the Convection Term:

• 1st-Order: First-order upwind scheme. This scheme scales the transported quantity by the upstream or downstream mass flow rate depending on flow direction. Only use when a higher-order scheme fails to give convergence, or in order to obtain an initial solution before switching to a higher-order scheme.
• 2nd-Order: Second-order upwind scheme. This scheme introduces linear interpolation of cell values on either side of the upstream or downstream face. Using this scheme can lead to poorer convergence properties, but gives accuracy as good as or better than the first-order scheme.
• MUSCL 3rd-Order/CD: Third-order upwind scheme. This scheme, which is valid for both steady and unsteady simulations, uses bounded differencing with an upwind blending factor to control the numerical dissipation in the scheme.

Secondary Gradients

There are two sources of secondary gradients in Simcenter STAR-CCM+ flow solvers:

• boundary secondary gradients for diffusion
• interior secondary gradients at cell faces

Use this property to control which gradients are included in the solver. On gives both gradients while Off excludes them. Interior Only and Boundaries Only select the corresponding gradients.

Flow Boundary Diffusion

When activated, diffusion is calculated across the flow boundary for all combustion scalars (for example, mixture fraction, mixture fraction variance, and progress variable).

Bounded Differencing

Only available when the Turbulent Flame Speed Closure (TFC) model property, Convection, is set to MUSCL 3rd-Order/CD.

Upwind Blending Factor

Specifies the proportion of upwind differencing, ${\varsigma }_{ubf}$ related to Eqn. (891).

The default value of this property is 1.0. Use lower values to reduce the numerical dissipation of the scheme.

Coefficient from Eqn. (3556). Unavailable when the Turbulent Flame-Speed Closure (TFC) Source Option property is set to User Defined Source.

Laminar Flame Speed

You select the turbulent flame speed method within the Turbulent Flame Speed Closure (TFC) > Turbulent Flame Speed node.

Method

Method	Corresponding Method Node
Turbulent Flame Speed - Zimont Selects the Zimont method (Eqn. (3580)) for calculating the turbulent flame speed source term.	Zimont Turbulent Flame Speed 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). See Turbulent Flame Speed. Unburnt Thermal Diffusivity Control The unburnt thermal diffusivity is defined as the laminar thermal conductivity divided by the product of specific heat and density, evaluated at the unburnt state. Flamelet Table The above properties are interpolated from the flamelet table. User Defined Profile Allows you to set this diffusivity as a scalar profile. Activates the User Defined Unburnt Thermal Diffusivity node. Power Law Determines the diffusivity using Eqn. (3486). Flame Stretch Effect When activated, uses the flame stretch factor $G$ (Eqn. (3581)), which takes the flame stretch effect into account by representing the probability of unquenched flamelets. Activates the Flame Stretch Effect node. Sub-Nodes Flamelet Table This node serves as a placeholder to indicate that the flamelet table provides values for the unburnt thermal diffusivity. User Defined Unburnt Thermal Diffusivity Use the Unburnt Thermal Diffusivity Profile sub-node of this node to set this diffusivity as a scalar profile. Flame Stretch Effect Constant, ustr Coefficient ${\mu }_{str}$ from Eqn. (3582). Critical Strain Rate Control Chemical Time Scale Method Activates the Chemical Time Scale Method node. User Defined Profile Activates the User Defined Critical Strain Rate node. Flame Stretch Effect: Sub-Nodes Chemical Time Scale Method Constant $B$ from Eqn. (3584). User Defined Critical Strain Rate The Critical Strain Rate Profile sub-node of this node functions as a scalar profile.
Peters Turbulent Flame Speed Selects the Peters method (Eqn. (3585)) for calculating the turbulent flame speed source term.	Peters Turbulent Flame Speed 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. (3586) Constant, A4 Coefficient $A_4$ , from Eqn. (3586) Constant, B1 Coefficient $B_1$ , from Eqn. (3586) Constant, B3 Coefficient $B_3$ , from Eqn. (3586) Ewald’s Corrector Constant $c_{ew}$ , from Eqn. (3586)
User Defined Turbulent Flame Speed Selects the User-Defined method for calculating the turbulent flame speed source term.	User Defined Turbulent Flame Speed 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.
User Defined Source Selects the User-Defined Source method for calculating the turbulent flame speed source term.	User Defined Source Progress variable source term. 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). Sub-Nodes User Source Profile Defines the Turbulent Flame-Speed Closure (TFC) progress variable source term. User Source Jacobian Profile Defines the Turbulent Flame-Speed Closure (TFC) progress variable Jacobian source term.

Initial Conditions

Progress Variable

You specify a progress variable between 0.0 (unburnt) and 1.0 (fully burnt).

Boundary Settings

Flow Boundaries

Flow boundaries except the Outlet have the Progress Variable physics value, a scalar profile, available by default.

Wall Boundary

Wall Combustion Scalar

Selects the scalars for the wall combustion calculation.

See Wall Combustion Scalar Option.

Region Settings

TFC Combustion Solver Properties

Under-Relaxation Factor

In order to promote convergence, this property is used to under-relax changes of the solution during the iterative process. If residuals show solution divergence and do not decrease, reduce the under-relaxation factor for the relevant solvers. The default value is 0.8.

Solver Frozen

When On, the solver does not update any quantity during an iteration. It is Off by default. This is a debugging option that can result in non-recoverable errors and wrong solutions due to missing storage. See Finite Volume Solvers Reference for details.

Reconstruction Frozen

When activated, Simcenter STAR-CCM+ does not update reconstruction gradients with each iteration, but rather uses gradients from the last iteration in which they were updated. Activate Temporary Storage Retained in conjunction with this property. This property is deactivated by default.

Reconstruction Zeroed

When On, the solver sets reconstruction gradients to zero at the next iteration. This action means that face values used for upwinding (Eqn. (905)) and for computing cell gradients (Eqn. (917) and Eqn. (918)) become first-order estimates. This property is Off by default. If you turn this property Off after having it On, the solver recomputes the gradients on the next iteration.

Temporary Storage Retained

When activated, Simcenter STAR-CCM+ retains additional field data that the solver generates during an iteration. The particular data retained depends on the solver, and becomes available as field functions during subsequent iterations. Deactivated by default.

Field Functions

The following field functions are only available when the TFC model is selected with a flamelet model.

Progress Variable

$c$ , in Eqn. (3535).

Progress Variable Variance

$c_{\mathrm{var}}$ , in Eqn. (3332).

Unnormalized Progress Variable

$y$ in Eqn. (3532).

Unnormalized Progress Variable Variance

$y_{\mathrm{var}}$ in Eqn. (3536).