[marina]

Hi everyone!

I'm trying to simulate in Fluent a 2D compressible flow around the NACA 0012, in order to study the velocity profiles in the boundary layer.

Reynolds=500000 and M=0.22

Boundary conditions:
- inlet: pressure-inlet (direction x)
- outlet: pressure-outlet
- top & bottom: symmetry

Turbulence: K-Epsilon. Intensity of turbulence: 3.1% and Lenght scale: 0.0976m

Solution method: Pressure-velocity coupling, scheme: coupled. Second order

After 15 iterations, three errors appear:
# Divergence detected in AMG solver: pressure coupled --> Decreasing coarsening group size!
# Divergence detected in AMG solver: pressure coupled --> Increasing relaxation sweeps!
# Divergence detected in AMG solver: pressure coupled --> Changing to W-cycle!

It also gives me some messages saying: turbulent viscosity limited to viscosity ratio of 10^5 in 1325 cells

I don't know what it means and how to solve it... I'm really desperated! :S Any ideas??

Thanks in advance!

[jonny_b]

Have you used the FMG initializer at all to get a good approximate starting solution for your case? The FLUENT documentation describes how to use it.

Also, try reducing your Courant number. The default is 200, try lowering that to between 50-100.

[marina]

I've already solve it!! I ran it in transient and it converged very well, then I changed to steady.
Anyway, thank you for your advice

[jonny_b]

Glad to hear you solved the problem! Your solution does work but I imagine it took a while for you to wait until the solution settled out. I would suggest trying the solutions I've mentioned above. They should help you get a converged steady state solution much quicker than performing a transient analysis.

[songlike163]

Originally Posted by marina

Hi everyone!

I'm trying to simulate in Fluent a 2D compressible flow around the NACA 0012, in order to study the velocity profiles in the boundary layer.

Reynolds=500000 and M=0.22

Boundary conditions:
- inlet: pressure-inlet (direction x)
- outlet: pressure-outlet
- top & bottom: symmetry

Turbulence: K-Epsilon. Intensity of turbulence: 3.1% and Lenght scale: 0.0976m

Solution method: Pressure-velocity coupling, scheme: coupled. Second order

After 15 iterations, three errors appear:
# Divergence detected in AMG solver: pressure coupled --> Decreasing coarsening group size!
# Divergence detected in AMG solver: pressure coupled --> Increasing relaxation sweeps!
# Divergence detected in AMG solver: pressure coupled --> Changing to W-cycle!

It also gives me some messages saying: turbulent viscosity limited to viscosity ratio of 10^5 in 1325 cells

I don't know what it means and how to solve it... I'm really desperated! :S Any ideas??

Thanks in advance!

Hi,I'm sorry to disturb you.I met the same problem while I'm learning CFD.How do you solve it?
Thanks in advance!