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.

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


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)


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

Boundary file

    type             patch;

Field file

    // 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


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


Source code:



  • Introduced in version 1.5