proudmanAcousticPower

Description

The proudmanAcousticPower function object computes the acoustic power due to the volume of isotropic turbulence using Proudman's formula.

The acoustic power, i.e. $P_A$ [W/m^3] in terms of turbulent kinetic energy, i.e. $k$, and turbulent kinetic energy dissipation rate, i.e. $\epsilon$ is given as:

$$P_A = \alpha_\epsilon \rho \epsilon M_t^5$$

where $\alpha_\epsilon = 0.1$ is a constant and

$$M_t = \frac{\sqrt{2 k}}{a_0}$$

with $a_0$ the speed of sound.

The acoustic power is also output in dB using:

$$L_P = 10 \log \frac{P_A}{P_{\ref}}$$

where $P_{\ref} = 1e^{-12}$ [W/m^3] is a constant.

Operands

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

Usage

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

proudmanAcousticPower1
{
    // Mandatory entries (unmodifiable)
    type            proudmanAcousticPower;
    libs            (fieldFunctionObjects);

    // Optional entries (runtime modifiable)
    alphaEps    0.1;
    // For incompressible flow simulations
    rhoInf      1.225;
    aRef        340;

    // 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: proudmanAcousticPower	word	yes	-
libs	Library name: fieldFunctionObjects	word	yes	-
rhoInf	Freestream density (for incompressible)	scalar	conditional	-
aRef	Speed of sound (incompressible)	scalar	conditional	-
alphaEps	Empirical model coefficient	scalar	no	0.1

The inherited entries are elaborated in:

• functionObject

Usage by the postProcess utility is not available.

Notes on entries

The freestream density and reference speed of sound are only necessary when a thermodynamics package is unavailable, typically for incompressible cases.

Further information

Tutorial:

• cavity

Source code:

• proudmanAcousticPower

API:

• Foam::functionObjects::proudmanAcousticPower

History: Introduced in version v1912