Code_Saturne_Automatic scheme and Low_Re_models Convergece

[C0st4s]

Hi,

Another 2 questions.
1) What is the scheme for the solver in equation parameters? (first choice before centred,upwind etc. in the GUI)
2) I am trying to run a heated channel flow case with low Reynolds number models (v2_BL_v2/k, Rij-epsilon EBRSM) and they do not converge. I run the case with high-Reynolds model (k-epsilon with 2scale wall function) and the results are fine for y+>30. They Retau is 1020, half channel width is 1.Any suggestions?


Thanks
Costas

[Yvan Fournier]

Hello,

For the scheme, do you mean what is the automatic choice ? I think it is centered for most variables, and upwind for turbulence variables such as k and epsilon, but I recommend checking in the listing and setup.log files.

Could you post the info recommended in the forum rules for the case which does not work ?

Regards,

Yvan

[and.desan]

Hi Costas,

I guess you are running steady-state simulations. Which algorithm are you using for pressure-velocity coupling? In my experience SIMPLE is quite unstable when using low-Reynolds models, even in basic planar channel flows. Switching to SIMPLEC (with a Courant value around 4.0, or even lower if necessary) improved the stability a lot.

Regards,
Andrea

[C0st4s]

Hi,

Thank you all for your replies. I actually used SIMPLEC for the pressure-velocity coupling. I found out that the Rij-espilon EBRSM requires GGDH hypothesis for the scalar temperature. For the rest of the models apparently there was an issue with my mesh which I sorted by splitting the geometry into half and using geometric progression (expansion ratio) in Salome mesh. I also changed the reference value that I initialise turbulence to higher (i.e 30 m/s) and it worked.
But I will check also the listing file and my courant number.

Costas.

[Ionut G]

Hi

What kind of scheme it is used for Pressure in the 'Scheme' tab from the 'Equation Parameters' menu?
I attached a picture too. showing the issue that I have.

Thank you,
Ionut

[Yvan Fournier]

Hello,

This is not an "issue". The pressure is not a convected variable, but handled in the velocity-pressure algorithm. You can check the theory guide if you need more details.

Regards,

Yvan