code_saturne User's Forum

HI
I'm doing a test with a fluid different from air, using seavater and an outfall injecting fluid in a very large box.
Thermophysical model is steady with one specie transported.
I set the for the moment the upper free surface of the box as an "imposed Pressure outlet" using the proposed value of 101300 considering a flow almost only parallel to the free surface and using gravity with
g_z=-9.81 m s^-1 and rho=999 Kg/m^3
Two hint:

• How to model the free surface boundary condition

• How to interpret the following result for the total pressure(the surface with -2.7E+04 is the free surface)

Hello,

For a free surface we commonly use a symmetry condition.

In your screenshot, the total pressure seems to match the hydrostatic pressure (which should be expected).

Regards,

Yvan

Yes the distribution inside the domain is Hydrostatic, as it should be.
But on the "imposed pressure outlet" would I expect something similar to 101300?

Hello,

The imposed pressure outlet condition applies to pressure, not total pressure if I am correct, so this may explain the difference. I am not certain, but the hydrostatic component of the total pressure probably depends on the elevation of the mesh (so it might not be a "physical" pressure, but is useful when shifted by a relevant, user/case defined constant).

Best regards,

Yvan

Hello,
If you want to model a free surface, you can also test the ALE module and then “free surface” boundary condition will be used.
It will impose p0 at the freesurface and let it move with the flow. So if you have breaking waves this method does not work.

We have also experimental options for that in version 6.0.

Best Regards
Martin

Martin FERRAND wrote: Thu May 30, 2019 1:42 pm Hello,
If you want to model a free surface, you can also test the ALE module and then “free surface” boundary condition will be used.
........

Thank you very much for the hint, the modelling of breaking waves is not necessary.
Summaryzing available in revision 5.0:

1. checking "mobile mesh" box in deformable mesh
2. in "definition of boundary region" selecting the now available option "Free surface"

Now the p0 pressure is applied to the movable free surface.
Is that all?