Flame Propagation
Simcenter STAR-CCM+ has two types of flame position models which you can use with all flamelet models—the Coherent Flame Model (CFM) and the Turbulent Flame Speed Closure (TFC) model. You can also use the TFC model with the Complex Chemistry model.
Each flamelet model describes how species and temperature is calculated in the flow field—it defines the species and temperature in the flame and after the flame. A flame position model is used to calculate the flame movement in space, for premixed and partially-premixed systems, through calculation of the turbulent flame speed.
You can select one of the following flame position models in Simcenter STAR-CCM+:
- Coherent Flame Model (CFM)
- Turbulent Flame Speed Closure (TFC)
The flamelet flame position models solve for the flame position by transporting a reaction progress variable. Normalized product species are used to define the reaction progress variable—so that it is zero for unburnt reactants and one for burnt products at chemical equilibrium.
Coherent Flame Model (CFM)
The CFM model solves an additional transport equation for the Flame Surface Density, which represents the extent of convolution of the premixed flame. The Flame Surface Density is then used to calculate the source term for the reaction progress variable. The CFM model is designed for simulating flames where the fuel and oxidizer are perfectly mixed before entering the computational domain.
To initiate combustion, the CFM model provides the Flame Area Density ignitor, accessible by right-clicking the node. While active, the Flame Area Density ignitor applies its specified value to the cells that are contained within the ignitor parts. When inactive, this ignitor does not affect the values of flame area density.
Turbulent Flame Speed Closure (TFC)
The TFC model uses an algebraic expression, called the turbulent flame speed, to calculate the source term for the mean reaction progress variable equation (for Flamelets) or the species (for Complex Chemistry).
- The flamelet TFC model provides the Progress Variable Ignitor that you access by right-clicking the node. While active, the Progress Variable ignitor applies its specified progress variable to the cells that are contained within the ignitor parts. When inactive, this ignitor does not affect the values of the progress variable.
- The complex chemistry TFC model provides the Fixed Temperature Ignitor that you access by right-clicking the node. When the Fixed Temperature Ignitor is on, the temperature that chemical reactions are evaluated at is set to the constant temperature defined in the Ignitors node.
- For any unsteady TFC setups, you can also use any of the spark models to initiate combustion.