turbulentInlet

Description

The turbulentInlet is a boundary condition that produces spatiotemporal-variant field by summing a set of pseudo-random numbers and a given spatiotemporal-invariant mean field. The field can be any type, e.g. scalarField. At a single point and time, all components are summed by the same random number, e.g. velocity components (u, v, w) are summed by the same random number, p; thus, output is (u+p, v+p, w+p).

The pseudo-random number generator obeys the probability density function of the uniform distribution constrained by the range [0:1]. The seed for the random number generator is hard-coded; therefore, it will produce the same sequence of random numbers at every execution.

$$x_p = (1 - \alpha) x_p^{n - 1} + \alpha (x_{ref} + c s R |x_{ref}|)$$

where:

Property	Description
$x_p$	Patch field
$x_{ref}$	Spatiotemporal-invariant patch scalar
$n$	Time level
$\alpha$	A scalar attempting to build two-temporal-point correlations by heuristically adding a fraction of the new random component to the previous time patch field
$c$	A heuristic automatically calculated correction term to compensate energy level losses due to the alpha scalar
$R$	Pseudo-random number [HARD-CODED seed]
$s$	Fluctuation scale (proportional to the xRef)

Usage

The condition requires entries in both the boundary and field files.

Boundary file

<patchName>
{
    type             patch;
    ...
}

Field file

<patchName>
{
    // Mandatory entries
    type             turbulentInlet;
    fluctuationScale <scalar>;               // the term `s` above
    referenceField   <scalarField>;          // the term `xRef` above

    // Optional entries
    alpha            <scalar>;               // the term `alpha` above

    // Inherited entries
    ...
}

where:

Property	Description	Type	Required	Default
type	Type name: turbulentInlet	word	yes	-
fluctuationScale	RMS fluctuation scale (fraction of mean)	scalar	yes	-
referenceField	Reference (mean) field	scalarField	yes	-
alpha	Fraction of new random component added to previous	scalar	no	0.1

The inherited entries are elaborated in:

• fixedValueFvPatchField.H
• Random.H

• This boundary condition should not be used for DES or LES computations as a turbulent velocity inflow condition, because the BC will not produce turbulence-alike time-series, and will decay almost immediately downstream of the inlet boundary although its historical name suggests the opposite.
• Nevertheless, the BC may be still used for other applications, e.g. as a uniform-random noise source in aeroacoustics.

Further information

Tutorial:

• pitzDaily

Source code:

• turbulentInlet

API:

• Foam::turbulentInletFvPatchField

History: Introduced in version 1.5