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-   -   Internal Compressible Flow: boundary conditions (http://www.cfd-online.com/Forums/openfoam-solving/94395-internal-compressible-flow-boundary-conditions.html)

francesco_capuano November 14, 2011 17:31

Internal Compressible Flow: boundary conditions
 
Hi everyone,

I have some problems in setting up the proper boundary conditions for an internal compressible flow (e.g. flow through a convergent-divergent nozzle), using a generic compressible solver like rhoSimpleFoam. I have found out that many OF users have encountered the same issues, so I think it would be nice if, once and for all, we could find a solution.

Tipically, such cases comprise, in addition to a wall (on which a no-slip condition is assumed), an INLET face and an OUTLET face. So the question is: what are the right boundary conditions to be set for p and U on such faces in order to reach a convergent solution?

Thanks in advance.

francesco_capuano November 15, 2011 10:53

Hi,

someone who could send a converged test case for a similar flow would be greatly appreciated.

Thanks

crixman November 18, 2014 06:39

Hi Francesco,
did you make any progress? I am trying to modify rhoSimplefoam as well as I am having problems with floating points due to thermal properties, maybe we can work on that together, let me know!

stosse November 21, 2014 05:51

Hi, guys!
I have been working on a similar problem for the last couple of weeks (using a modified version of the fireFoam solver), and have had severe difficulties getting a correct flow field with a module with inflow/outflow. I have tried many different configurations, but what has worked for me is to use totalPressure BCs for p_rgh with a pressure gradient between the inflow and outflow patch, and pressureInletOutletVelocity for U.

p_rgh:
Quote:

outlet
{
type totalPressure;
rho rho;
psi none;
gamma 1.4;
p0 uniform 101275;
value uniform 101275;
}
inlets
{
type totalPressure;
rho rho;
psi none;
gamma 1.4;
p0 uniform 101325;
value uniform 101325;
}
I am not very experienced with OpenFOAM, so this is a result of trial and error. It would be nice if some more experienced users know why this setup (compressible flow, inlet and outlet) is so unstable.

Regards,
Sindre

crixman November 21, 2014 14:44

Hi Sindre, thank you for sharing your findings, would try it out when I have some free time!


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