The uniformMixed is a boundary condition that provides β€˜mixed’ type boundary condition that mix a uniform fixed value and a uniform patch-normal gradient condition. The term β€œuniform” is a legacy name since the prescribed values were previously spatially uniform across that patch.


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

Boundary file

    type            patch;

Field file

    // Mandatory entries
    type            uniformMixed;

    // Optional entries
    uniformValue    <Function1<Type>>;
    uniformGradient <Function1<Type>>;

    // Conditional entries

        // if 'uniformValue' and 'uniformGradient' entries are set
        uniformValueFraction    <Function1<scalar>>;

    // Inherited entries


Property Description Type Required Default
type Type name: uniformMixed word yes -
uniformValue Uniform fixed values Function1<Type> no -
uniformGradient Uniform gradient values Function1<Type> no -
uniformValueFraction Fraction values Function1<scalar> conditional -

The inherited entries are elaborated in:

  • fixedGradientFaPatchField.H
  • Function1.H

  • This boundary condition allows lazier definitions so that either or both: uniformValue and uniformGradient must be defined. If only of these entries is defined, the value fraction is automatically treated appropriately (ie, 0 with \c uniformGradient and 1 with uniformValue). If both uniformValue and uniformGradient are defined, the uniformValueFraction must also be defined.
  • The value entry (optional) is used for the initial values. Otherwise the function(s) are used for the evaluation. In some cases (eg, coded or expression entries with references to other fields) this can be problematic and the value entry will be needed.

Further information


  • N/A

Source code:



  • Introduced in version v2306