# How to impose a flux at the inlet ?

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 November 22, 2010, 12:15 How to impose a flux at the inlet ? #1 Senior Member   Cyprien Join Date: Feb 2010 Location: Stanford University Posts: 261 Rep Power: 11 Hi ! I want to set up an equation from the knowledge of a flux. My equation has the following form: Code: `ddt(S)+div(phib)=0` phib is evaluated otherwise. As inlet boundary condition, I want to impose a constant flux phib0. Moreover with such inlet, I have been told that S do not need any BC. Is there a simple manner to do that ? Best regards, Cyp

 December 2, 2010, 06:28 #2 Senior Member   Cyprien Join Date: Feb 2010 Location: Stanford University Posts: 261 Rep Power: 11 Hi everybody! I am still on this problem : i do not succeed to impose a flux at the inlet without set up a BC fixedValue for my field S... May be I should try a specific BC ?? which one ? I hope you can unblock me.... Regards, Cyp

 January 26, 2011, 04:27 #3 New Member   Gert Jan Auwerda Join Date: Jan 2011 Posts: 3 Rep Power: 8 Hi I have the exact same question. I have a CFD problem where I have a fixed mass flux at the inlet and a fixed pressure at the outlet. As the pressure at inlet will depend on flow properties, the inlet pressure is not known in advance. As the density depends on this pressure, I do no know the inlet velocity. So is there a velocity BC, which lets me input a fixed (total) flux, from which inlet velocity BC is derived? I can make a decent guess of course, but I want to be exact. And running the code a few times, adjusting manually my inflow BC seems a really stupid way. I cannot believe this BC does not exist, it is so common in CFD problems! Please help!

 January 27, 2011, 03:22 #4 Member   Join Date: Jun 2010 Posts: 33 Rep Power: 9 Hello, do you mean? boundaryField { Inlet { type flowRateInletVelocity; flowRate 2.8; // [kg/s] value uniform (0 0 0); // only place holder } Regards, Ralph

 January 27, 2011, 04:05 #5 New Member   Gert Jan Auwerda Join Date: Jan 2011 Posts: 3 Rep Power: 8 Ah yes, that is the one I was looking for. Thank you very much!

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