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Description

The activePressureForceBaffleVelocity is a velocity boundary condition to simulate the opening or closure of a baffle due to area averaged pressure or force delta, between both sides of the baffle. This is achieved by merging the behaviours of wall and cyclic baffles.

Usage

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

Boundary file 

<patchName>
{
    type            patch;
    ...
}

Field file 

<patchName>
{
    // Mandatory entries
    type            activePressureForceBaffleVelocity;
    cyclicPatch     <word>;
    openFraction    <scalar>;
    openingTime     <scalar>;
    maxOpenFractionDelta <scalar>;
    minThresholdValue <scalar>;
    forceBased      <bool>;
    opening         <bool>;

    // Optional entries
    p               <word>;

    // Inherited entries
    ...
}

where:

Property Description Type Required Default
type Type name: activePressureForceBaffleVelocity word yes -
cyclicPatch Name of cyclic patch used when the active baffle is open word 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 -
minThresholdValue Minimum value for the active baffle to start opening scalar yes -
forceBased Flag to activate force based baffle bool yes -
opening Flag to decide if baffle is opening or closing (1 opening, 0 closing) bool yes -
p Name of pressure field word no p

The inherited entries are elaborated in:

  • fixedValueFvPatchField.H

Method

The baffle joins two mesh regions, where the open fraction determines the interpolation weights applied to each cyclic- and neighbour-patch contribution. This means that this is boundary condition is meant to be used in an extra wall beyond an existing cyclic patch pair.

The baffle is activated when the area weighted pressure difference between master and slave patches is larger then minThresholdValue.

Once the threshold is crossed, the baffle is activated and continues to open or close at a fixed rate using:

\[x = x_{old} + s \times \frac{dt}{DT}\]

where:

Property Description
\(x\) Baffle open fraction [0-1]
\(x_{old}\) Baffle open fraction on previous evaluation
\(s\) Sign for orientation: 1 to open or -1 to close
\(dt\) Simulation time step
\(DT\) Time taken to open the baffle

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

Further information

Tutorial:

Source code:

API:

History:

  • Introduced in version 1.5