Chemistry Acceleration Properties

Chemistry Acceleration

When the In Situ Adaptive Tabulation and the Clustering properties are activated at the same time, accuracy can be reduced. Therefore, if In Situ Adaptive Tabulation is activated, deactivate Clustering. ISAT is not available when using Dynamic Mechanism Reduction.

In Situ Adaptive Tabulation: When this option is activated, a Chemistry Acceleration > In Situ Adaptive Tabulation node appears in which you can specify the ISAT tables.
Clustering: When this option is activated, a Chemistry Acceleration > Clustering node appears in which you can specify the clustering components.
Dynamic Mechanism Reduction: When this option is activated, a Chemistry Acceleration > Dynamic Mechanism Reduction node appears in which you can specify the parameters for reducing the number of species in the mechanism that are solved for by the CVODE solver.

In Situ Adaptive Tabulation

Tabulates computationally expensive functions and then interpolates these at run time. You can use ISAT to retrieve approximate values for multi-dimensional functions that are expensive to compute. See In Situ Adaptive Tabulation.

Absolute Tolerance: Absolute tolerance for the ISAT approximation.
Table Size (MB): Maximum size for the ISAT table.
Sensitivity Absolute Tolerance: The absolute tolerance of the CVODE solver which computes the sensitivity matrix that is used in the ISAT approximation.
Sensitivity Relative Tolerance: The relative tolerance of the CVODE solver which computes the sensitivity matrix that is used in the ISAT approximation.

In Situ Adaptive Tabulation Context Menu

Clear ISAT Table: Clears all of the internal ISAT tables and statistics (such as: adds, retrieves, and grows).

Clustering

Components

The available clustering components are listed below—default clustering components are marked with an asterisk*. For unsteady simulations, the chemistry time-step is the flow time-step—which is constant and therefore unavailable for clustering.

[available species]
Chemistry Time Step*
Entropy
Equivalence Ratio*
OH* (when present)
Mixture Fraction
Pressure
Progress Enthalpy
Static Enthalpy
Temperature*
TFC Reaction Rate*
TFC Unburnt Progress Variable (this is the Unburnt Unnormalized Progress Variable)
[User Component n]
X Co-ordinate
Y Co-ordinate
Z Co-ordinate

[Clustering Component] Properties

Tolerance

Allows you to specify the tolerance of the component for clustering.

Tolerance Type

There are two ways to specify the clustering table resolution for any clustering variable:

Relative: The clustering bin size is calculated as the maximum of that variable in the computational domain minus the minimum, which is then multiplied by the Relative Tolerance, $ε_{r e l}$ in Eqn. (3430).
Absolute: The clustering bin size is the Absolute Tolerance, $ε_{a b s}$ in Eqn. (3431).

Dynamic Mechanism Reduction

If the complex chemistry approximation option, Relax to Chemical Equilibrium, is activated, the dynamic mechanism reduction option is unavailable.

Error Tolerance: The lower the number, the closer the solution is to that of the full chemical mechanism—less species are removed from the mechanism. Higher values exclude a greater number of species from the solution, which is therefore less accurate.
Imposed Target Species: Species that you select from the full chemical mechanism that are target species for the Directed Relation Graph (DRG) algorithm Eqn. (3433). These species are always included in the reduced chemical mechanism.; If the species, NO, is present in a mechanism, it is automatically included in the target species.
Minimum Number of Target Species: The minimum number of target species (including the imposed target species). If this value is greater than the number of Imposed Target Species, the remaining target species are taken to be those with the fastest reaction rates.