Learning Forum

[DaAu]

Hello together

I am trying to simulate a liquid free jet in a gas.  The goal is to model the amplitude of the free surface. In real test the phenomenon is stationary.

In the following principle sketch my boundary conditions are shown.

I use an ICEM CFD mesh with 12 million cells. The quality of the mesh is as follows:

I calculate with the following settings:

The residuals look like this:

The monitor of the mass flow at the outlet looks like this:

Monitor points with the pigginess look like this:

I always get the following message:

"Experiencing convergence difficulties - temporarily relaxing and trying again..."

What could be the reason for this message? The simulation takes an extremely long time for one iteration.
Is it possibly due to the mesh?
Are there ways to speed up the convergence? 
If I compare the inlet and outlet I get this: 

Why is the residual of the mass balance still so bad?

Thank you very much
Greetings

[Rob]

Aspect ratio is very high if the free surface cuts across one of those cells. 

Please post VOF and velocity contours on the centre plane.  

You can try dropping the Courant Number to nearer 10, but the issue may be that the model is transient - multiphase flows often are.