The Q
function object computes the second invariant of the velocity gradient tensor [ \(s^{-2}\)]:
\[ Q = \frac{1}{2}\left[\left(\mathrm{tr} \left(\grad \u\right)\right)^2 - \mathrm{tr} \left(\grad \u \dprod \grad \u\right)\right] \]
Q
iso-surfaces are good indicators of turbulent flow structures.
Operand | Type | Location |
---|---|---|
input | volVectorField | $FOAM_CASE/<time>/<inpField> |
output file | - | - |
output field | volScalarField | $FOAM_CASE/<time>/<outField> |
Example of the Q
function object by using functions
sub-dictionary in system/controlDict
file:
Q1 { // Mandatory entries (unmodifiable) type Q; libs (fieldFunctionObjects); // Optional (inherited) entries field <inpField>; 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: Q | word | yes | - |
libs | Library name: fieldFunctionObjects | word | yes | - |
The inherited entries are elaborated in:
Example by using the postProcess
utility:
postProcess -func Q
The Q field is stored on the mesh database, using the default name
Q
If the field
entry is set to a value other than U
, the default name becomes
Q(<field>)
This can be overridden using the result
entry.
Tutorial:
channel395DFSEM
tutorial: $FOAM_TUTORIALS/incompressible/pimpleFoam/LES/channel395DFSEMSource code:
Related:
History