activePressureForceBaffleVelocity

Description

The activePressureForceBaffleVelocity is a velocity boundary condition that simulates 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.

The baffle joins two mesh regions, where the open fraction determines the interpolation weights applied to each cyclic- and neighbour-patch contribution. This 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

$$x = x_{old} + s \, \frac{\Delta t}{T}$$

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]
$s$	Sign for orientation: 1 to open or -1 to close

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                  activePressureForceBaffleVelocity;
    cyclicPatch           <word>;
    orientation           <label>;
    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: 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	-
minThresholdValue	Min absolute pressure or force difference for activation	scalar	yes	-
forceBased	Force (true) or pressure-based (false) activation	bool	yes	-
opening	Baffle is opening (true) or closing (false)	bool	yes	-
p	Name of pressure field	word	no	p

The inherited entries are elaborated in:

• fixedValueFvPatchField.H

Further information

Tutorial:

• flamePropagationWithObstacles

Source code:

• activePressureForceBaffleVelocity

API:

• Foam::activePressureForceBaffleVelocityFvPatchVectorField

History: Introduced in version 2.0.0