fieldAverage

Description

The fieldAverage function object computes ensemble- and/or time-based field averages, with optional windowing, for a user-specified selection of volumetric and/or surface fields.

Fields are entered as a list of sub-dictionaries, which indicate the type of averages to perform, and can be updated during the calculation. The current options include:

• mean: arithmetic mean

$$\overline{x} = \frac{1}{N}\displaystyle\sum\limits_{i=0}^N x_i$$

• prime2Mean: prime-squared mean

$$\overline{x'}^2 = \frac{1}{N} \displaystyle\sum\limits_{i=0}^N (x_i - \overline{x})^2$$

• base: average over 'time', or 'iteration' (N in the above)
• window: optional averaging window, specified in 'base' units

Average field names are constructed by concatenating the base field with the averaging type, e.g. when averaging field 'U', the name of resultant fields becomes:

• arithmetic mean field, UMean
• prime-squared field, UPrime2Mean

Note that averaging is performed per cell. If the mesh is moving, e.g. a rotating body within a static outer mesh, cells in the rotating region will sample different regions of space which may lead to unexpected/non-continuous field average results.

Information regarding the number of averaging steps, and total averaging time are written on a per-field basis to the <functionObject name>Properties dictionary, located in <time>/uniform.

When restarting form a previous calculation, the averaging is continuous or may be restarted using the restartOnRestart option.

The averaging process may be restarted after each calculation output time using the restartOnOutput option or restarted periodically using the periodicRestart option and setting restartPeriod to the required averaging period.

With the subRegion option, also supports fields on function object surface output (e.g., sampledSurfaces).

Operands

Operand	Type	Location
input	{vol,surface}<Type>Field(s)	$FOAM_CASE/<time>/<inpField>s
output file	-	-
output field	{vol,surface}<Type>Field(s)	$FOAM_CASE/<time>/<outField>s

where <Type>=Scalar/Vector/SphericalTensor/SymmTensor/Tensor.

Usage

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

fieldAverage1
{
    // Mandatory entries (unmodifiable)
    type            fieldAverage;
    libs            (fieldFunctionObjects);

    // Mandatory entries (runtime modifiable)
    fields
    (
        <field name 1>
        {
            mean        <yes|no>;
            prime2Mean  <yes|no>;
            base        <time|iteration>;
            windowType   exact;
            window       10.0;
            windowName   <name>;
            allowRestart true;
        }
        ...
        <field name N>
        {
            mean        <yes|no>;
            prime2Mean  <yes|no>;
            base        <time|iter>;
       }
    );

    // Optional entries (runtime modifiable)
    restartOnRestart    false;
    restartOnOutput     false;
    periodicRestart     false;
    restartPeriod       0.002;

    // Optional (inherited) entries
    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: fieldAverage	word	yes	-
libs	Library name: fieldFunctionObjects	word	yes	-
fields	Names of the operand fields and averaging options	dict	yes	-
restartOnRestart	Restart the averaging on restart	bool	no	false
restartOnOutput	Restart the averaging on output	bool	no	false
periodicRestart	Periodically restart the averaging	bool	no	false
restartPeriod	Periodic restart period	scalar	conditional	-
restartTime	One-shot reset of the averaging	scalar	no	GREAT
subRegion	Name for alternative objectRegistry	word	no	""

The inherited entries are elaborated in:

• functionObject
• fieldAverageItem

Usage by the postProcess utility is not available.

Stored properties

Fields

Average fields are stored on the mesh database, using the default name constructions:

<field>Mean
<field>Prime2Mean

These are written to the standard time directories according to the writeControl setting.

Further information

Tutorial:

• pitzDaily
• throttle
• freeSpacePeriodic

Source code:

• fieldAverage

API:

• Foam::functionObjects::fieldAverage

History: Introduced in version v1606+