Learning Forum

[FaizanYounas]

Hi! I'm modelling the case of bubble rise. I have drawn the CAD model and meshed in Gambit. It works fine in fluent, but when I scale my mesh down (because my bubble size is in mm) and again run the simulation it didn't work and said floating point exception.

Does anyone know what could be the possible reason?

[Rob]

Did you initialise then scale or scale and initialise? What boundary settings are you using?

[FaizanYounas]

I have tried both these. I'm using VOF + LEE model. I also tried running the simulations with just VOF, but it didn't run. Even I tried with very robust boundary conditions, but nothing worked.

[Rob]

How small is "small". How much mesh have you got? What time step size did you use?

[DrAmine]

What are your BC's?

[FaizanYounas]

I have made the mesh in Gambit and imported into fluent (by default the fluent take the values in "m"). I want to convert it into "mm" so I choose the scaling factor of x and y as "0.001". The mesh got converted into
"mm" in fluent but the simulation didn't run. I even reduce the time step size to 1e-5 but it didn't work.
My BC's are VOF (implicit and explicit both tried) with surface tension as 0.05 N/m. Also, SIMPLE+Geo-Reconstruct+First Order with time step as 1e-5.

[DrAmine]

VOF is not a BC: Are you using Source Terms, Boundary Fluxes..? Can you do a mesh check? Can you do the scaling in Gambit and try then in Fluent? If the velocity scale is the same and just now changing the mesh from meter to mm you will need to reduce the time step size so that you get same CFL. But please do all checks first.

[Rob]

Don't scale in Gambit! 's too young to remember it.... But do check the mesh in Gambit before switching to Fluent. Why (how) are you still using Gambit? It's been obsolete for over 10 years, we use Workbench or Fluent Meshing now.

[DrAmine]

:D :D

[FaizanYounas]

Solved! I didn't do anything different and it just work. I don't know if it is relevant or not but since I started using the 2021 R1 version alot of strange things happened like this. I did some research and came to know that 2021 R1 version fluent has some bugs. I don't know how much true is this. But I have tried some problems in old fluent (18.1) and it worked fine their. Anyways, thank you guys for your help. You are of great help!

[DrAmine]

Any software contains bug like any other product. Glad that it is working for you.