code_saturne User's Forum

Hello everyone,

I am trying to run a LES study of a buoyancy driven flow. Previously I ran a few RANS simulations of the same case, and I observed that most of the fields showed a chequered pattern unless I activated IPHYDR and IPUCOU.
In a first exploratory LES, I am back to the same situation, but the options that fixed the problems are not compatible (in version 4.0.8), with the second order time scheme which is the default for LES.
In your experience, what would be the suggested course of action in this scenario? Is it recommended to switch back to a first order time scheme, or is there a sounder approach?
Thanks to anyone replying.
Cheers,

Cosimo

Dear Cosimo,

If you have the option the use a more recent build of Code_Saturne, you could try to flag your temperature as buoyant (key "is_buoyant") so it will be updated in the Velocity-Pressure loop. Combined with an increased NTERUP, it could potentially improve your results.

Can you confirm that the checkerboard pattern appears only when using a second-order time scheme and does not appear when using a first-order time scheme? Are you using default values for the Rhie and Chow filter?

Regards,
Cedric