Flux boundary condition

alicharchi · February 23, 2017, 13:37

Dear all,
I am solving electron continuity equation and need to assign a kind of flux boundary condition for some patches. This flux itself is a function of several other parameters.
My problem is that this flux is not diffusive and I can not relate it to gradient and use mixed type BC.
Is there a way for directly assigning flux boundary condition in OF? I know that in basic finite volume it is a straightforward task.

Thanks,
Ali

babakflame · February 25, 2017, 21:51

Ali,

Can you give a little more description of the BC formula?

this link will help you type in latex:
Guide: Writing Equations in LaTeX on the CFD Online Forums

If its a Robin type boundary condition follow this link:
http://www.modlab.lv/docs/2011/OpenF...Vilums_pdf.pdf

Regards

alicharchi · February 27, 2017, 10:33

Babak,
This is the expression for the flux:
$\Gamma_{e} = - \mu_{e} N_{e} \overrightarrow{E} - \frac{1}{4} N_{e} v_{th,e}$
Where
$\Gamma_{e}$ is the flux
$\mu_{e}$ is the electron mobility
$N_{e}$ is the electron number density
$\overrightarrow{E}$ is the electric field
and $v_{th,e}$ is the thermal velocity

I am looking for a way to directly assign the flux instead of expressing it as a function of gradient.

babakflame · February 28, 2017, 14:12

Ali,

At the moment I am working on sth very similar to yours. I am looking at $Foam_SRC files to get an idea.
I will share my findings with you.

Regards

babakflame · March 4, 2017, 12:15

Ali,

what you can do in these situations is redefining your boundary condition in your solver , i.e. for instance when your code sees a specific patch name or specific boundary type, assign a predefined boundary condition for that patch. This is done through refCast<> template in OpenFOAM. I have written a snippet for it which still casts error, However this is the approach I am aware of.

You can find it here:Snippet for redefining fixedGradient boundary condition for a patch inside solver

Regards

February 23, 2017, 13:37	Flux boundary condition	#1
alicharchi New Member Ali Charchi Join Date: Oct 2013 Location: South Carolina, USA Posts: 8 Rep Power: 12	Dear all, I am solving electron continuity equation and need to assign a kind of flux boundary condition for some patches. This flux itself is a function of several other parameters. My problem is that this flux is not diffusive and I can not relate it to gradient and use mixed type BC. Is there a way for directly assigning flux boundary condition in OF? I know that in basic finite volume it is a straightforward task. Thanks, Ali

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February 25, 2017, 21:51		#2
babakflame Senior Member Bobby Join Date: Oct 2012 Location: Michigan Posts: 454 Rep Power: 15	Ali, Can you give a little more description of the BC formula? this link will help you type in latex: Guide: Writing Equations in LaTeX on the CFD Online Forums If its a Robin type boundary condition follow this link: http://www.modlab.lv/docs/2011/OpenF...Vilums_pdf.pdf Regards

February 27, 2017, 10:33		#3
alicharchi New Member Ali Charchi Join Date: Oct 2013 Location: South Carolina, USA Posts: 8 Rep Power: 12	Babak, This is the expression for the flux: $\Gamma_{e} = - \mu_{e} N_{e} \overrightarrow{E} - \frac{1}{4} N_{e} v_{th,e}$ Where $\Gamma_{e}$ is the flux $\mu_{e}$ is the electron mobility $N_{e}$ is the electron number density $\overrightarrow{E}$ is the electric field and $v_{th,e}$ is the thermal velocity I am looking for a way to directly assign the flux instead of expressing it as a function of gradient.

February 28, 2017, 14:12		#4
babakflame Senior Member Bobby Join Date: Oct 2012 Location: Michigan Posts: 454 Rep Power: 15	Ali, At the moment I am working on sth very similar to yours. I am looking at $Foam_SRC files to get an idea. I will share my findings with you. Regards

March 4, 2017, 12:15		#5
babakflame Senior Member Bobby Join Date: Oct 2012 Location: Michigan Posts: 454 Rep Power: 15	Ali, what you can do in these situations is redefining your boundary condition in your solver , i.e. for instance when your code sees a specific patch name or specific boundary type, assign a predefined boundary condition for that patch. This is done through refCast<> template in OpenFOAM. I have written a snippet for it which still casts error, However this is the approach I am aware of. You can find it here:Snippet for redefining fixedGradient boundary condition for a patch inside solver Regards