[TahminehAd]

I am trying to reach a convergence for my simulation in cfx and at the same time I want to keep the simulation time as short as possible. To reach a good convergence, I increased the number of meshing in my simulation. Now my question is should I also reduce my time step significantly to get good results?
In another word, my question is what is the relation between the number of nodes or mesh size and time steps of the simulation?

[Opaque]

There is no specific relationship; however, the finer the mesh, the higher the chances of capturing finer "vortices" or flow regions that were not present in the coarser mesh.

The more complex the flow, the higher need for smaller timesteps.

[ghorrocks]

You need to do a time step sensitivity check for each mesh refinement to work out the time step requirement for each mesh.

An alternative is to use adaptive time stepping, homing in on 3-5 coeff loops per time step, and then it will find its own time step size for the mesh. This also accounts for the convergence criteria and and any other complexities in the model so is a quick and effective way of getting the correct time step.