Convergence
 

Hi,

My case of a rotaing flow inside a tank doesnt seem to converge. However all values I monitor like pressures and velocities become completely flat. This is both with standard as second order for pressure to solve. Can somebody advise?

It sounds like you have it converged as good as it will for the mesh you have created. It is good that you have monitor points in addition to looking at the residuals. Have you conducted a mesh independence study? That would be the next step. Look at the flow field that you computed and make sure you resolve the regions that still have high residuals (you can look at contours of residuals in the Fluent results).

This could indicate a problem with the setup or model you are using. You may want to try adjusting the boundary conditions or grid settings and double-checking all the input parameters to make sure they are correct.

It seems like you may have reached the practical convergence limit for your current mesh. Even though the residuals aren't dropping further, the monitor point values stabilizing is a good sign that the solution is usable. As others have suggested, I would try a mesh independence study to refine the mesh, focusing on areas that still show high residuals. Adding more mesh resolution in the rotating region and near walls/boundaries could help with overall convergence. You can also double-check that the boundary conditions, numerical schemes, and other simulation settings are optimal. Start with your best practices setup, then try tweaking settings one by one to see if convergence improves. The mesh is likely the main factor though. With a q-edge mesh, you should see the residuals drop further and get a more fully converged solution.

it sounds like you've tried several troubleshooting steps for your rotating flow simulation, which is great. Convergence issues can definitely be frustrating with CFD models.

Since you mentioned this is a model of flow inside a tank, I'm wondering if you've checked whether the flow is becoming unsteady at any point, creating periodic vortices or turbulence that could prevent convergence. I recently ran into a similar situation when modeling air flow around an electric vehicle charging station. Small vortices were shedding off the charger and causing ev charger overheating. Adding some artificial dissipation helped damp out those unsteady effects. So if your model involves any bluff bodies or curved surfaces, that may be something to look into.

Of course, it's hard to say for sure if that applies to your specific case without more details. But I hope reviewing boundary conditions, refining the mesh, and ruling out unsteady flow effects can ultimately help get your model to converge. Feel free to provide any other updates or info about your tank geometry, flow parameters, etc. Convergence issues are a rite of passage in CFD, but we can work through it!