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Description

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.

We determine 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:

\[x = x_{old} + \text{sign}(\vec{F}_{net}) \frac{\Delta t}{T}\]

where:

Property Description
\(x\) Baffle open fraction [0-1]
\(x_{old}\) Baffle open fraction on previous evaluation [0-1]
\(\Delta t\) Simulation time step [s]
\(T\) Time taken to open the baffle [s]
\(\vec{F}_{net}\) Net force across the baffle [N]

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

Usage

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

Boundary file 

<patchName>
{
    type            wall;
    ...
}

Field file 

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

    // Optional entries
    p                     <word>;

    // Inherited entries
    ...
}

where:

Property Description Type Required Default
type Type name: activeBaffleVelocity word yes -
cyclicPatch Name of cyclic patch word yes -
orientation Flag to switch flow direction, either 1 or -1 label yes -
openFraction Current open fraction of patch [0-1] scalar yes -
openingTime Time taken to open the baffle scalar yes -
maxOpenFractionDelta Max open fraction change per timestep scalar yes -
p Name of pressure field word no p

The inherited entries are elaborated in:

  • fixedValueFvPatchField.H

Further information

Tutorial:

  • N/A

Source code:

API:

History:

  • Introduced in version 1.6