[aravind vashista]

I am using the k-w model for turbulence and I am solving a problem involving 3 annular jets. I use the coupled model and second-order discretization scheme for pressure and other variables. I use a default courant number of 200 and the solution converged. However, the paper that I am validating solved the problem using the Hybrid RANS-LES scheme using open foam having courant number of 0.8. I have the following doubts
1. Does courant number depends on grid
2. Does the courant number depend on type of turbulence model and solution strategy? (That is coupled solver)
3. If i decrease my CFL number below 10 my solution is not stable and I am getting reversed flow at outlet which is incorrect. I would like to know why the residuals wont convegre for low CFL number

[vinerm]

The Courant number used in Coupled solver is not CFL criterion. Default value is 200 and you can use higher (1000s of times higher) or lower values, however, a value as low as 10 does not make sense. If case can converge with a value of 10, then even SIMPLE will work. Just use a higher value or enable Pseudo-Transient. That is more stable.

[LuckyTran]

Already answered by vinern but I'm going to repeat it anyway just to be clearer

There is no "CFL number." Quit making up terms. You only confuse yourself. Use the words on the screen.

Courant number does depend on the grid.

The Flow Courant number in the COUPLED P-V solver is a type of under-relaxation. High Flow Courant numbers means you converge faster. If you set super low Flow Courant numbers, you need many more iterations to converge per time-step. I like to use 2e7 for the Flow Courant number so it converges in 1 iteration like PISO.

Regardless of what number you set the Flow Courant number to, it doesn't affect your Courant number (which is determined by your grid and time-step size).

[aravind vashista]

I now understood the difference between flow courant number and the actual courant number. However, I would like to know the maximum and minimum limits of my cell courant number. I have seen that we can see this in histogram plot under the velocity function. However, it is not visible in my case. I am using Ansys Fluent 16.0 . Is there any other way to see cell courant number?

[LuckyTran]

Can you make a contour plot of the Courant number? The same way you would make a pressure plot, etc?

The Courant number is a field available for all unsteady solvers. I'm not sure why you're not able to see it. There isn't anything fancy you have to do.

[aravind vashista]

I am solving steady state problem not unsteady