[rabat]

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

[m zahid]

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

[FluidsExpert]

Did you happen to find a solution. I also wish to define a zero-gradient boundary condition in Star CCM+.

Harun.

[vivekcfd]

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.