[michso]

I am trying to adjust dnsFoam to calculate the decay of turbulence (in space). For that, in my domain (say 32, 16, 16 - with inlet bc) the turbulence forcing is active in the first half only (1:16,1:16,1:16), the other part should be calculated without the extra source term. How can I do that in a compact and elegant way? Some CFD codes allow to define different fluid zones, is that a case with OF? I've got no experience with OF and need some help

Regards,
Mick

[sampaio]

A possible way to do this (far from clever, tough ) is to create a new scalar field (say, alpha) to act like a switch:
it is 0 outside your forcing subdomain and 1 inside.

Then you set the initial conditions accordingly and never change this variable (alpha).

In the main code, you multiply alpha by the force, and that's it.

Cheers,
luiz

[mattijs]

Please post your message under one topic only.

Mattijs

[michso]

Luiz,
That's indeed my question. How to create such a scalar field to be 1 in the first half of the domain and 0 in the second. Could you give me an example?

Regards,
Mick

[sampaio]

Add your switch variable (alpha) to createFields.H

volScalarField alpha
(
IOobject
(
"alpha",
runTime.timeName(),
mesh,
IOobject::MUST_READ,
IOobject::AUTO_WRITE
),
mesh
);


Your "0" directory must now contain initial value for this variable all over the domain. Set it to 0 over all domain and boundary conditions.

Then, create a auxiliar case, whose geometry is exactly that of your forcing subdomain. Construct such a case and set alpha = 1 in all this auxiliary geometry (case).

Use mapFields utility to map fields from the auxiliary case to the real one:

mapFields . auxiliar_case . real_case

This way, your variable alph (dont forget to alter mapFieldsDict accordingly) will now be 1 in the region coincident with the auxiliar case geometry and 0 elsewhere.

Then, run the case (real one)

Good luck

[pierre]

the setFields utility might be helpful. Have a look at the dam break tutorial for the interFoam solver. You can also look at the guide. Hope this helps.

[michso]

Luiz, Pierre,
Thanks a lot for your prompt reactions and valuable remarks. I think that now I will be able to go further with my project.

Cheerio,
M

[michso]

Guys,
What is great about our life is that solving one problem creates at least 2 new ;-).
Anyway, I simply overlooked that Kmesh generates the forcing field based on the entire geometry. My idea is to generate non-zero forcing for the half of my domain only (e.g. 16 16 16) and solve the problem in a bigger domain (32 16 16). As mentioned in the first post I have got no experience with OF and rather little with C programming (especially using OF macros). Does anyone know how to fool Kmesh and consequently UOprocess to take only the half of my domain to generate forcing?

Regards,
Mick