This Error usually occurs when FLUENT is running recently: Error:divergence detected in AMG solverressure correction. And there is nothing unconventional in residual graphics. Why? Which factors may lead to this error?

The error indicates that the solver has crashed. If the solve crashes within a few iterations of starting the simulation the issue is in the boundary/initial condition.

First make sure the length scales of the model are as required. If you are solving for compressible flow start with a lower mass flow and increase the mass flow to design value in small steps.

More details can be discussed if we know what kind of case you are solving.

Regards, Ananth

Thank you! The issue I want to solve is to simulate convective heat transfer in circular tube. An 2d symmetric model is adopted. The mesh close to the wall is fine ,and it's coarse near the axis correspondingly. The solve crashs occur not only at the beginning of iteration , but also after more than one hundred iterations.

What about level of residuals?

What is "level of residuals",and how to get it?

see to resiadual monitor.

The level of residual I set is about 1e-08