[Far]

I am simulating low pressure turbine unsteady flow and I have couple of questions:

1. How to decide time step for the implicit solver?

2. Do we need to satisfy CFL < 1 for implicit solver?

3. Why implicit solver is preferred in commercial codes and as I understand for unsteady flows explicit solver would be better option.

4. Or explicit solver is only efficient in LES where turbulent scales to be resolved are the same order as the time step dictated by CFL < 0.2 condition?

5. For the same geometry and flow, time step is inversely proportional to Reynolds number?