[spk]

Hi guys,
I'm new in OpenFOAM and i would like to solve a 2D orifice geometry using the dsmcFoam solver. Has anyone used this solver before?
I will honestly appreciate any advice or help!!!
Thanks

[anon_a]

Well, you need to provide some more information.
What are your boundary conditions?
The pressure BC is not implemented by default and you have to program it
(modify src/lagrangian/dsmc/submodels/InflowBoundaryModel/FreeStream/FreeStream.C to read n from a dictionary for each incoming patch).

Also, are you sure you need this solver? What is your Kn number upstream?
The dsmcFoam solver can not deal with 2D AXISYMMETRIC flows,
which means that you have to turn to 3D, increasing the computational cost.
Just trying to help you avoid expensive calculations.

If you need some specific information, let me know

[spk]

Hi anon_a,
thank you for your answer!
The boundary conditions are:
pressure inlet: absolute pressure 1000 Pa
pressure outlet: vacuum
orifice diameter 0.5 mm
The gas density and the orifice size correspond to the entire regime from free molecule to continuum flow.
If you want and have time i could send you via email an isodensity contours of gas through the orifice solving this problem with Prof. Bird's DS2V program.
I just want to know can i solve the same problem with openFoam?
and if yes, is it easy? because i am new user in OpenFoam!!
Thanks a lot!
spk

[anon_a]

Yes, you can solve the problem you mention with dsmcFoam.
It needs a little bit of modification but it can be done relatively easy.

Two quick ways of simulating open boundaries with specified pressure
were given at the same time I was replying to you in this thread:

http://www.cfd-online.com/Forums/ope...am-vacuum.html

The first method is only appropriate for vacuum BCs.
The second way is better (but requires the compilation of the code each time you change the boundary number density).

Personally, I would advise to study the code and try to change it in a general manner, using dictionaries. Deeper knowledge really helps to fine tune your runs.

[spk]

I would like help about boundary conditions!

First about inlet. I have pressure 1000 Pa and velocity 0 m/s.
So in folder 0, in file boundaryU i wrote for inlet (in order to define velocity):
type fixed value;
value uniform (0 0 0);
In folder 0, in file rhoN i wrote for inlet (in order to define pressure):
type fixed value;
value uniform <particle number density corresponding to the pressure value>;

Then about outlet. I have vacuum!
in file boundaryU i wrote for outlet:
type calculated;
value uniform (0 0 0);

Are these right?? How can i define the pressure in vacuum?

[anon_a]

Did you read the link I gave you?
Did you have trouble applying it?

[spk]

Hi anon_a!

I think i cant apply the second method because i dont know the desired outlet number density.
The first method is something that i proposed with the previous post?

[anon_a]

The number density that you provide to DSMC in the boundaries is not the number density that you expect to have there. Instead, it is the number density that characterizes the incoming stream. Therefore, a vacuum boundary condition means that there are no INCOMING molecules from that surface (and not "no molecules at all").

Therefore, for a vacuum BC, you just need to specify that no molecules are coming in the domain, which can be done with the methods of that post.

EDIT: and this is not done by the rhoN, rhoM, dsmcRhoN files.

[spk]

In the file FreeStream.C what value i have to enter for the desired inlet number density and outlet?
The only value known is the input particle number density for inlet and vacuum for outlet.
Please help i'm new OpenFOAM user!

[murali]

hi foamers


im new here to OpenFoam this is my knusden number 0.113 and mean free path at .0068m this is my dimension .1x.06x.06m .and then where i going mention this value in dsmcFoam.(0,constant,system)

[murali]

hi foamers

i am doing my project related to hypersonic flow, therefore anyone know the hypersonic flow corner dsmc code or have?

[jiaoxiaolei]

Hi, murali, there is a case in dsmcFoam, it is the same as yours, you can have a look

[murali]

hi carl


thanks to reply which case is similiar to my cases.