[Omish]

Do I get fake convergence by lowering current number (just like lowering relaxation factors)??
What is exactly courant number in a simple and apprehensible explaination?

[LuckyTran]

The Courant number is how far information/disturbances travel in one time-step. When the Courant number is >>1, your disturbance has the potential to skip through the mesh, which leads to many interesting problems (including numerical instability). Having a smaller Courant number actually improves the accuracy of your simulation because you are better able to track the evolution of these disturbances.

URF's are a different monster and better to interpret in a steady-state example. URF's affect only the convergence behavior and do not improve your accuracy. They are artificial/numerical bandaids to prevent a simulation from becoming unstable.

[Omish]

My simulation is also steady state,I’m just using “coupled” scheme and courant appears in “solution control”.
So how could it be interpreted in a steady state case?

[LuckyTran]

The Courant number in the COUPLED P-V scheme is actually a URF but has the interpretation of a Courant number multiplier. Check out this post #14 which has some equations to convert from this Courant number to URF's. A Courant number of Infinity corresponds to a URF of 1. Depending on the version of Fluent you use, the default Courant number is 200 or 100 which are close to a URF of 0.99. In this steady state example, lowering the Courant number does get you fake convergence just as lowering a URF would.

[Omish]

Thanks so much