# Zero gradient pressure @ pressure outlet Boundary

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 March 23, 2009, 08:55 Zero gradient pressure @ pressure outlet Boundary #1 New Member   Join Date: Mar 2009 Location: Belgium Posts: 13 Rep Power: 8 Hi, I got a back flow in pressure outlet boundary. To avoid the back flow in starccm+, we can change the boundary condition with the user-code, somethings like zero gradient pressure @ outlet. Did anyone programme the zerogradP in c or fortran? How can I solve this probleme? Thanks in Advance, Rabat ehsan-rezvanian likes this.

 November 17, 2014, 09:30 hi #2 Member   Qureshi M Z I Join Date: Sep 2013 Posts: 54 Rep Power: 3 have u find the answer, about setting "zero pressure gradient boundary condition" ? i want to set the zero pressure gradient at outlet, could u please share with me your experience, how can i set this ? regards

 January 21, 2015, 19:31 Zero-Gradient boundary condition Star CCM+??? #3 New Member   ANON Join Date: Oct 2010 Posts: 2 Rep Power: 0 Did you happen to find a solution. I also wish to define a zero-gradient boundary condition in Star CCM+. Harun.

 January 28, 2015, 08:50 #4 Member   Vivek Kumar Join Date: Mar 2009 Location: Switzerland Posts: 34 Blog Entries: 1 Rep Power: 8 It is quite straight forward to implement this boundary condition in starccm+. 1) You create new field function e.g. called PresCC (Pressure at cell centers) and assign variable \$Pressure to it. Very important=>=> Do not forget to select option "Ignore Boundary Values". This way your new variable PresCC at the boundaries has the values of pressure next to the boundary. 2) Now go to the outlet boundary and select Field Function option and select PresCC as the pressure at the outlet boundary. In this way you will set pressure at boundary equal to the pressure at the center of the boundary control-volume. This is what a zero-gradient boundary means. But I still suggest to first try to extend your outlet in order to avoid with the back flow before trying zero-gradient boundary for the pressure. ehsan-rezvanian likes this.

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