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hack - using porous region to fix local instability

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Old   August 14, 2021, 10:49
Default hack - using porous region to fix local instability
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ufocfd
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I recently had some dodgy cells which were causing some very spikey convergence and creating some flow instability in the region due to very high unphysical velocity at particular location. If you dont want to fix the mesh (for whatever reason) you can apply some porosity in the area to stabilise the flow. You just need to apply "topoSet - latestTime" (to create a cell zone), and then modify the fvOptions file (to apply some porosity to that cell zone). Its not an ideal approach but quite a useful "hack" if you need a quick fix sometimes. I found it gave an instant and significant improvement of the convergence and flow solution. I wonder if there are any other methods?

topoSetDict:
actions
(
// radiator cell set
{
name radiator_cellSet;
type cellSet;
action new;
source sphereToCell;
sourceInfo
{
centre (0.45 0.014 0);
radius 0.03;
}
}
// radiator cell zone
{
name radiator_cellZone;
type cellZoneSet;
action new;
source setToCellZone;
sourceInfo
{
set radiator_cellSet;
}
}
);

fvOptions:
porosity1
{
type explicitPorositySource;
active yes;

explicitPorositySourceCoeffs
{
muName mu;
type DarcyForchheimer;
selectionMode cellZone;
cellZone radiator_cellZone;

DarcyForchheimerCoeffs
{
d d [0 -2 0 0 0 0 0] (1e10 1e10 1e10); // viscous
f f [0 -1 0 0 0 0 0] (0 0 0); // inertia

coordinateSystem
{
type cartesian;
origin (0 0 0);
coordinateRotation
{
type axesRotation;
e1 (1 0 0);
e3 (0 1 0);
}
}
}
}
}
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convergence, hack, instability, mesh quality, porosity

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