[spalartallmaras]

Hallo,

I do a calculation about a spray bar and there is a problem from boundary condition. It is 3D simulation and with VOF Model and Schnerr-Sauer Cavitation Model.



The surface with 3 is my outlet.

Initial Condition: Volume Fraction of Gas in the first cylinder is zero. And the VF is 1 in the last two cylinders.
BC at 1 is velocity inlet with 3 m/s and normal to boundary
BC at 2 is velocity inlet with -2,75 m/s and normal to boundary.

But problem is, if I set a BC at 3 with pressure outlet, then
after the spray from the middle cylinder to the third cylinder there is a back flow from 3 in the third cylinder.

BC at 3 is
-gauge pressure=0
-normal to boundary
-turbulent options: Default
-Backflow volume fraction for gas=1





Actually I think I set all options at BC 3 right, but I can not understand there is strong backflow from outside to third cylinder. Physically the spray should go out. Can anybody suggest, what is the reason?

Regards,
Amugae