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March 19, 2013, 02:42 
About GroovyBC

#1 
Member
M Mallikarjuna Reddy
Join Date: Jul 2012
Posts: 91
Rep Power: 6 
Hi Foamers,
I am using OpenFOAM2.1.1 version. My solver is steady state and i prepared it by modifying "simpleFoam" solver. I am facing problem with boundary condition for the scalar field (lets say T). The governing equation for the field T as follows: Code: solve ( fvm::div(phi, T) + fvc::div(J) ); At the fixed Walls i need to apply zero flux boundary condition. In the above equation "J" is the flux. So i need to apply J.n=0 at fixed walls. I have little experienced in handling "groovyBC". Can anyone help me how to write this expression. Thanks in advance. Regards M Mallikarjuna Reddy 

March 19, 2013, 06:04 

#2  
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Bernhard Gschaider
Join Date: Mar 2009
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Quote:
Assuming that J is a surface field then fvc::div(J) only uses the values on the boundary patches (the situation is not better if J is a volumefield). Anyway: if you're not doing completely different physics to somebody else then J is somehow related to grad(T) which makes the second term boil down to something like laplacian(lambda,T) for which you can use the fvmform which makes everything much more stable. If J is completely unrelated to T then only the actual value of div(J) in the cells matters for the solution of the Tequation and if J is a vector and J=(0,0,0) is not good enough for you then a slipboundary condition is sufficient
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March 19, 2013, 07:57 

#3  
Member
M Mallikarjuna Reddy
Join Date: Jul 2012
Posts: 91
Rep Power: 6 
Quote:
Dear gschaider, Thanks for the quick response. In my case i defined J as volume field: Code:
volVectorField J ( IOobject ( "J", runTime.timeName(), mesh, IOobject::NO_READ, IOobject::NO_WRITE ), f1*fvc::div(Epnn1)+fvc::laplacian(f2, U) ); Quote:
Quote:
Moreover i am struggling with divergence problem. From your valuable suggestion I understood that there is divergence in my case since J is defined as a volume field. Should I define J at the surface field to achieve convergence? Thanks Reddy 

March 19, 2013, 09:00 

#4  
Assistant Moderator
Bernhard Gschaider
Join Date: Mar 2009
Posts: 4,005
Rep Power: 43 
Quote:
For convergence: i can only be general here: you mentioned that the functions fX depend on T: the best strategy would be to identify the parts that depend on T, linearize them, put these parts implicitly into the Tequation using fvmoperations and only put the rest of the terms into the explicit source. Also sit down with pen and paper and see if the BC for J can be expressed in terms of T on the boundary. Then implement that BC for T. If you insist on having an allexplicit source term the way you do now you may need veeeery small timesteps (probably) Yeah: if you know what you're doing a surfaceScalarfield for the flux is better than a volVectorfield (see creation and usage of phi in the regular solvers)
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March 20, 2013, 06:55 

#5  
Member
M Mallikarjuna Reddy
Join Date: Jul 2012
Posts: 91
Rep Power: 6 
Quote:
Thanks for your reply. I'll go through your suggestion and let you know if i succeed. Thanks Regards Mallikarjuna Reddy 

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