code_saturne User's Forum

Hi,

In Code Saturne, can I define a density for the user scalar equation, instead of using the density employed by the continuity, momentum and energy equations?

In my simulation, I have set up several user scalars, and I want to use constant densities for different scalar equations, however the fluid density is a variable as a function of the temperature and pressure. So I'm wondering if I can specify different densities for the user scalars, but didn't manage to find where can I do that. I've just found that I can edit the diffusivities for each user scalar through field_get_val_s, can I do the same to the density through it?

Thanks,
Xiaoxue

Hello,

I don't believe this is possible, as we solve a single Navier-Stokes eaquation, considering a single velocity and pressure field.

For different scalars such as a gas mix, the usual approach is to use scalars to define the or fraction of each gas (since the sum of fractions must be 1, solving for n-1 scalars might be better), and compute the mixture density based on the relative fractions and densities.

We do need to make this easier to use, as there already is a "gas mix" model in the code, but only usable through user subroutines, and only with constant species properties.

Regards,

Yvan

Hi Yvan,

I'm using the user subroutines for my simulation.

The different scalars I've mentioned are not for the fluid mixture, but for additional fields I need to solve. The fluid density in my simulation is defined variable as a function of the temperature and the pressure, however I want the density for the user scalars are constant.

Actually I've just learned from the doxygen there is a variable "kromsl" serves as the "variable density field id key for scalars", but it is only available in version 5, and I'm using version 4 now. I'm wondering if that means I can define variable densities for each scalar through the field id "kromsl"? I'll try it after installing a version 5.

Thanks for your reply.

Regards,
Xiaoxue