Learning Forum

[scabo]

Hi

I have run a 3D pipe flowith unsteady, simple and fixed time step scheme. I want to calculate the Co number after the simulation has converged. For that I have used mag(U)*dt/dx as a custom field func. But dx varies with location inside the pipe so how to get dx as a function of space? Alternatively is there any thing else for Courant no? for eg there is one cell convective Co in the dropdown but I dont think its same as the CFL number. Any help is greatly appreciated.

thanks

[Rob]

For each cell or for the whole domain? The Cell Courant Number will be covered in the User's Guide, and if not I can't comment on it's definition. 

[scabo]

The courant no will vary with cell right becasue each cell has different flow velocity and cell size. So i want the distribution of Co on the cross-section. I hope you get it?

[Rob]

Yes. So you need to use a CFF with cell length and velocity. 

[scabo]

Yes but cell length is not available to choose as a variable in Fluent for use in CFF.

[Rob]

Correct. What do you think would be a good replacement to that? 

[scabo]

Normally we can use the smallest cell length(cube root of minimum volume under perform mesh check) but thats a rough calcualtion because in areas where the cell is not equal to that minimum value, all the values outputted by Fluent are wrong. So you may need to lower the time step that what is actually needed which can increase computation cost. I find this very annoying.