I am trying to simulate airflow through a duct and out grilles. When i run the simulation it ends pretty quickly and reads Flat lines detected in Convergence Monitor - Auto Stop. in the message window. There is no flow through the duct or out the grilles? What does Flat lines detected in Convergence Monitor - Auto Stop. mean and how would i fix it?
The flat lines message means your simulation completed successfully:
Sounds like you have not set up the flow correctly.
A picture would be helpful here. As long as different regions of your geometry are connected and have same material, there is no other boundary condition needed.
The message your reported is actually an indication that SimCFD thinks the average value plots have flattened. If you are not happy with the current convergence, you can always adjust the setting of Solve >> Solution Control >> Automatic Convergence Assessment as tight, or even unclick it and stop the iterations when you see the lines flatten.
Hi, you don't need to do anything between the interface of two like fluid materials. Sim CFD would treat it as one fluid domain.
I once imported a duct model from revit and ran an analysis. My duct was modelled along with the AC. I applied a volume flow rate at the inlet duct surface but forgot to suppress my solid AC. Hence, the inlet became a wall and there was no flow and the solver stops immediately after a few iterations. Could this be your case?