[Divine]

Hi
we are trying to simulate a free jet from a converging sonic nozzle
problems
1.divergence is detected
2.reverse flow
we think that the problem is due to boundary conditions
check the attachments for geometry and mesh

[MB72]

As far as I can understand is a problem of boundary.
You could solve switching the boundary condition to an "open boundary", which can handle flow coming back from openings.
You need to read carefully the FLUENT documentation in order to decide the right boundary condition in this case and some hints regarding the downstream mesh size.

And please check also the mesh quality. FLUENT is very sensitive to this aspect too.

[Divine]

hi
Thank you for replying.
Well, i have changed the boundary conditions, took two inlets(check the mesh).
The inlet boundary i have given the pressure as 1013250pa and the supersonic gauge pressure as 1010000pa and same for the second inlet as well. At the outlet i have taken ambient condition 101325.the problem that occours while simulation is that time step- time step reduced in 1 cells due to excessive temperature change-
Is there any solution for this ??

[MB72]

My suggestion:
Try to start with a reduced pressure drop: for instance try to use a higher pressure at outlet (few hundred Pa less than inlet) and make the simulation converge. Next reduce the outlet pressure step by step.

Make also sure that your fluid model is OK for such pressure and pressure drop (density, viscosity, turbulence ...) or you will have very inaccurate results.