MachNo

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:

• functionObject
• fieldExpression

Example by using the postProcess utility:

postProcess -func MachNo

Further information

Tutorial:

• cavity

Source code:

• MachNo

API:

• Foam::functionObjects::MachNo

History: Introduced in version v1606+