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Description

The MachNo function object computes the Mach number as a volScalarField.

The Mach number is a dimensionless quantity representing the ratio of flow velocity past a boundary to the local speed of sound:

\[M = \frac{|\u|}{\sqrt{\gamma p/\rho}}\]

where:

\(M\)
Mach number
\(\u\)
Velocity
\(\gamma\)
The ratio of specific heat of a gas at a constant pressure to heat at a constant volume
\(p\)
Static pressure
\(\rho\)
Fluid density

Operands

Operand Type Location
input volVectorField $FOAM_CASE/<time>/<inpField>
output file - -
output field volScalarField $FOAM_CASE/<time>/<outField>

Usage

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

MachNo1
{
    // Mandatory entries (unmodifiable)
    type            MachNo;
    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: MachNo word yes -
libs Library name: fieldFunctionObjects word yes -

The inherited entries are elaborated in:

Example by using the postProcess utility:

postProcess -func MachNo

Further information

Tutorial:

Source code:

API:

History: