The convergence criterion changes from simulation to simulation (e.g. a validation project requires a tighter convergence than a simulation to get qualitative aspects of a flow field). So the criterion is up to the practitioner.
In Numerics > residual controls, you can input residuals criteria to automatically stop the simulation. If all residuals drop under the input values, the software automatically deems your simulation converged:
You, however, shouldn’t only rely on residuals to assess convergence. You can set a variety of Result Controls (in the simulation tree) to monitor key parameters. These parameters of course will depend on your simulation. It can be temperature at the outlet, drag and lift coefficients etc etc etc. And then you should also inspect the solution fields looking for anomalies.
The two main meshers are standard and hex dominant. Hex dominant is OF’s SnappyHexMesh.
You can set controls for y+ right here:
You’ll need a converged simulation to assess y+ in the post processing environment.