blendingFactor

Description

The blendingFactor function object computes and stores the blending coefficient employed by blended divergence schemes, giving an indicator as to which of the schemes is active across the domain.

Blended schemes combine contributions from two schemes, i.e. $\phi_1$ and $\phi_2$, using a weight field, i.e. $w$, such that the effective scheme value, i.e. $\phi_\eff$, is computed as follows:

$$\phi_\eff = w \phi_1 + (1 - w) \phi_2$$

It follows that when $w = 1$, the scheme reduces to $\phi_\eff = \phi_1$; similarly, when $w = 0$, the scheme reduces to $\phi_\eff = \phi_2$.

The weight field, i.e. $w$, is surface field and converted to a volume field for easier post-processing by setting the cell value to one minus the minimum of the face values:

$$w_c = 1 - \min_{\forall i \in \mathrm{faces}}\left(w_{f,i}\right)$$

This conversion leads to blending indicator field whose values mean:

0   =  scheme 0
1   =  scheme 1
0-1 =  a blend between scheme 0 and scheme 1

Operands

Operand	Type	Location
input	-	-
output file	dat	$FOAM_CASE/postProcessing/<FO>/<time>/<file>
output field	volScalarField	$FOAM_CASE/<time>/<outField>

Usage

Example of the blendingFactor function object by using functions sub-dictionary in system/controlDict file:

blendingFactor1
{
    // Mandatory entries (unmodifiable)
    type            blendingFactor;
    libs            (fieldFunctionObjects);

    // Mandatory (inherited) entry (runtime modifiable)
    field           <field>;

    // Optional entries (runtime modifiable)
    phi             phi;
    tolerance       0.001;

    // Optional (inherited) entries
    result          <fieldResult>;
    region          region0;
    enabled         true;
    log             true;
    timeStart       0;
    timeEnd         1000;
    executeControl  timeStep;
    executeInterval 1;
    writeControl    timeStep;
    writeInterval   1;
}

where the entries mean:

Property	Description	Type	Required	Default
type	Type name: blendingFactor	word	yes	-
libs	Library name: fieldFunctionObjects	word	yes	-
field	Name of the operand field	word	yes	-
phi	Name of flux field	word	no	phi
tolerance	Tolerance for number of blended cells	scalar	no	0.001

The inherited entries are elaborated in:

• functionObject
• fieldExpression
• writeFile

Usage by the postProcess utility is not available.

Notes on entries

The field and phi entries are used to construct the scheme name to lookup from the fvSchemes dictionary, as:

div(phi,U)

The tolerance entry is used as a threshold when computing the number of cells identified as using each scheme. The tolerance entry must be in the range 0 to 1, excluding the endpoints.

Stored properties

Fields

The blending factor is stored on the mesh database, using the default name:

blendingFactor(<field>)

The name can be overridden by using the result entry.

Further information

Related:

• Courant number blended scheme

Tutorial:

• cavity

Source code:

• blendingFactor

API:

• Foam::functionObjects::blendingFactor

History: Introduced in version v1606+