[HorstvanGrass]

Hi there,
ist there a minimum for the Mach number in pressure far field boundary condition? Because for Pressure 90000 and Mach 0.1 there is no chance for convergence. Increased quality and simplified the mesh but residuals won't decrese. By looking for residuals contours of velocity and turbulance modell, they are very high in the complete mesh, what I find doesn't make so much sense. With a badder mesh and Mach over 0.3 it's super easy converging.
So is it possible that's I have to refine it so much to get the little compressible effects or is it just not possible with this boundary condition.


Thx in advance!

[LuckyTran]

There isn't a low mach number limit.

You have a general problem unrelated to the type of boundary condition. Maybe your initial condition is bad or your solver settings not tuned. But it's not because the boundary condition is not working. Whatever you are doing, you got lucky with the higher Mach numbers and unlucky with the super low Mach numbers.

[AlexFlow]

Originally Posted by HorstvanGrass

Hi there,
ist there a minimum for the Mach number in pressure far field boundary condition? Because for Pressure 90000 and Mach 0.1 there is no chance for convergence. Increased quality and simplified the mesh but residuals won't decrese. By looking for residuals contours of velocity and turbulance modell, they are very high in the complete mesh, what I find doesn't make so much sense. With a badder mesh and Mach over 0.3 it's super easy converging.
So is it possible that's I have to refine it so much to get the little compressible effects or is it just not possible with this boundary condition.


Thx in advance!

The secret is to reduce all relaxation factors in "Controls" to below 0.25.
Some applications are unstable and need to run more slowly to achieve convergence.
I had the same problem and was reading your question, then I found a solution!
If you encounter issues, try setting second-order discretization in "Methods".