# Impose a flux at BC for the transport of a scalar

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 March 28, 2012, 10:08 Impose a flux at BC for the transport of a scalar #1 Senior Member   Cyprien Join Date: Feb 2010 Location: Stanford University Posts: 262 Rep Power: 11 Hi! The problem looks very simple. I want to impose a flux at the inlet of a domain. My solver is made of an advective-diffusive equation : Code: ```fvScalarMatrix TEqn ( fvm::ddt(T) + fvm::div(phi,T) -fvm::laplacian(DT,T) );``` I know that I can get the corresponding flux from TEqn.flux() Code: `surfaceScalarField phiT = TEqn.flux();` How can I impose a value to this flux at the inlet of my domain ? In that case, the BC velocity is non-zero and consequently the usual trick using fixedGradient can't work. I thought of something like Code: ` phiT.boundaryField()[patchID] == Q;` but this doesn't work (of course...) May be something like Code: ` (TEqn.flux()).boundaryField()[patchID] == Q;` (but it doesn't compile...) Is anybody has an idea ?? Best regards, Cyp

 March 28, 2012, 10:18 #2 Member   Cedric Van Holsbeke Join Date: Dec 2009 Location: Belgium Posts: 81 Rep Power: 10 Giving a calculated value to a boundary can be achieved using the codedFixedValue boundary condition (http://www.openfoam.org/version2.0.0...me-control.php).

 March 28, 2012, 13:05 #3 Senior Member   Cyprien Join Date: Feb 2010 Location: Stanford University Posts: 262 Rep Power: 11 Thank you for your reply. Indeed I read the information about codedFixedValue, but I do not know how this can satisfy my request.. I think that imposing a flux should be a very easy thing in finite volume method..

 May 22, 2012, 15:04 #4 Senior Member   Arne Stahlmann Join Date: Nov 2009 Location: Hanover, Germany Posts: 209 Rep Power: 11 Hi Cyprien, any progress so far? I'm struggling with the same problem for a couple of days now, but also have not yet found a way of directly imposing a flux. I need a flux and zero-flux boundary condition, but within the solver. So far, in my case I could manage it with a source/sink term in the patch nearest cells, but that is not exactly what I wanted. Greeting, Arne

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