The activeBaffleVelocity is a velocity boundary condition that simulates the opening of a baffle due to local flow conditions, by merging the behaviours of wall and cyclic conditions. The baffle joins two mesh regions, where the open fraction determines the interpolation weights applied to each cyclic- and neighbour-patch contribution.


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

Boundary file

    type            patch;

Field file

    // Mandatory entries
    type            activeBaffleVelocity;
    cyclicPatch     <word>;
    orientation     <label>;
    openFraction    <scalar>;
    openingTime     <scalar>;
    maxOpenFractionDelta <scalar>;

    // Optional entries
    p               <word>;

    // Inherited entries


Property Description Type Required Default
type Type name: activeBaffleVelocity word yes -
cyclicPatch Name of cyclic patch used when the active baffle is open word yes -
orientation Orientation (1 or -1) of the active baffle patch label yes -
openFraction Current fraction of the active baffle which is open scalar yes -
openingTime Time taken for the active baffle to open scalar yes -
maxOpenFractionDelta Maximum fractional change to the active baffle openness per time step scalar yes -
p Name of pressure field word no p

The inherited entries are elaborated in:

  • fixedValueFvPatchFields.H

  • The orientation is used to change the direction of opening without the need for reordering the patch faces.


It is determined whether the baffle is opening or closing from the sign of the net force across the baffle, from which the baffle open fraction is updated using:

\[x = x_{old} + sign(F_{net})\frac{dt}{DT}\]


Property Description
\(x\) Baffle open fraction [0-1]
\(x_{old}\) Baffle open fraction on previous evaluation
\(dt\) Simulation time step
\(DT\) Time taken to open the baffle
\(F_{net}\) Net force across the baffle

The open fraction is then applied to scale the patch areas.

Further information


  • N/A

Source code:



  • Introduced in version 1.5