# zero-diffusion (constant gradient) boundary condition

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 July 26, 2011, 08:39 zero-diffusion (constant gradient) boundary condition #1 New Member   Tom Witten Join Date: May 2011 Location: Freiberg Posts: 10 Rep Power: 6 Hi all, I'm still relatively new to openfoam and despite searching through the tutorials, source code, and this forum have not been able to determine if the zero-diffusion boundary condition is available in openfoam or easily implemented. Has anyone used this type of boundary condition in openfoam before? Cheers, Tom

 July 26, 2011, 18:01 #2 Senior Member   Cyprien Join Date: Feb 2010 Location: Stanford University Posts: 230 Rep Power: 9 Hi Tom, and welcome on board! I believe that the BC you are looking for is zeroGradient. You just have to write " type zeroGradient;" within our patch. @++ Cyp

 July 27, 2011, 04:53 #3 New Member   Tom Witten Join Date: May 2011 Location: Freiberg Posts: 10 Rep Power: 6 Hi Cyp, Thanks for the reply! What I'm looking for though is the zero-diffusion outlet boundary condition, not the zero-gradient boundary condition. A zero-diffusion boundary condition is of the form d^2(phi)/d(n^2) = 0 where phi is a transported variable (e.g. a component of velocity, temperature, viscosity, ...). Typically when this condition is set at an outlet, the value of the node at a particular outlet position is calculated from the interior situated nodes as well as the first derivative which is some constant. I think both fluent and cfx allow implementation of this boundary condition and wanted to know if openfoam also has this option as I would like to test openfoam for a few studies. Cheers, Tom

 July 27, 2011, 07:35 #4 Senior Member     Anton Kidess Join Date: May 2009 Location: Delft, Netherlands Posts: 919 Rep Power: 17 Thomas, have a look at this thread: Second Derivative Zero - Boundary Condition

 July 29, 2011, 04:59 #5 New Member   Tom Witten Join Date: May 2011 Location: Freiberg Posts: 10 Rep Power: 6 Thanks akidess, that's what I was looking for

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