Hi, im doing a flow simulation with compressible gas (air) but at higher flow rate something always goes wrong.

Until about 7 l/min everything looks good, the pressure start convergence, ∆P is about 0,5 bar what looks realistic, but over 8 l/min the pressure goes up

independently from the initial Flow rate, and keep the raising  until i stop the simulation manually. (so its hard to belive that ~15% more flow can make infinite pressure)

With more flow so like 10-15 l/min the different is only that the pressure goes up faster.

I tried to refine the mesh or rerun it with a bigger environment (longer inlet and the outlet as a big box) but the result is always the same.

Can someone help about about explain this difficulties and how to solve them?