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-   -   Lagrangian track not support empty patch interaction? (http://www.cfd-online.com/Forums/openfoam-solving/62970-lagrangian-track-not-support-empty-patch-interaction.html)

 su_junwei March 24, 2009 20:54

Lagrangian track not support empty patch interaction?

Dear All

It seems that the Lagrangian track methods in OpenFOAM don't support the empty patch. How to treat particle behaviors the 2D geometry with empty patch with these methods?

Junwei

 niklas March 25, 2009 03:15

hmmm....tracking in 2D. not a good idea if you ask me.
And here's why.

Lets look at the for instance the momentum (mass and energy will suffer the same problem).
When we calculate the momentum gain/loss for the particle and transfer that to the gas the change in gas velocity will depend on the thickness of your 2D-slab.

If you make the slab very thick the gas will hardly feel the influence of the particles because the gas volume in 1 cell will be quite high.
On the other side, if you make it very very thin, the volume of the gas can be even less than the volume of the particle, hence the transferred momentum to the gas will result in a very fast respons on the gas.

If you do a 2d calculation on wedge you will have similar problem, a drop far from the axis of symmetry will influence the gas less than if its close to the center.

I hope that illustrates the problem.

 su_junwei March 25, 2009 06:47

Exactly Niklas

But there are some cases where a 3D simulation is more computational demanding especially for dense disperse flow, fluidized bed for instance. A possible way is using a pseudo 3D simulation with a direction with thickness equaling to the particle diameter.

If we treat the front and back plane as a wall, it will of course influence the continuous phase flow. It is better to make it an empty patch and do the simulation. In such a situation, removing the normal component of the velocity when encountering the empty patch can be a feasible way.

Junwei

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