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-   -   SimpleFoam results as initial condition to rhoSimpleFoam (http://www.cfd-online.com/Forums/openfoam-pre-processing/126627-simplefoam-results-initial-condition-rhosimplefoam.html)

 marcelorl November 21, 2013 19:07

SimpleFoam results as initial condition to rhoSimpleFoam

Hi All,

Is it possible to use a incompressible results as a initial condition to a compressible case? (I know that there is difference in the pressure dimension and there are different fields for each case).
I am currently using rhoSimpleFoam to solve the problem, but I am having a lot of convergence problems. So, I would like to know if it is possible to run the problem with simpleFoam and use the fields as initial condition to rhoSimpleFoam.

Thank you for the help.

Regards,

Marcelo

 doctorV November 21, 2013 21:05

I had a lot of convergence troubles with rhoSimpleFoam and rhoSimplecFoam. What are you simulating? Is it an airfoil or an internal flow? Anyway if you don't set right boundary conditions solver will crash for sure.

 marcelorl November 22, 2013 13:45

Quote:
 Originally Posted by doctorV (Post 463020) I had a lot of convergence troubles with rhoSimpleFoam and rhoSimplecFoam. What are you simulating? Is it an airfoil or an internal flow? Anyway if you don't set right boundary conditions solver will crash for sure.
I am working on a labyrinth seal. My boundary conditions are pressure defined in the inlet and outlet. As I know it is very unstable boundary condition, I put zero gradiente for pressure in the inlet and changed the velocity until the pressure goes to 10 MPa.Outlet is pressure (8Mpa) defined and zero gradient for velocity. the velocity residual is ok, but the pressure is oscilating and i have tried everything that i could without success.
Do you know anything that I can try?

Thank you very much for the help.

 doctorV November 22, 2013 14:17

Could you post some pictures of your mesh? The solution to your trouble is in a Lilek-Peric-Demirdzic paper of 1993: it's about SIMPLE algorithm corrected for compressible flows. It shows boundary conditions of ducted flows for subsonic, transonic and supersonic cases. If you don't use right boundary conditions, solver run will explode for sure: remember the nature of problems (elliptic, hyperbolic, parabolic). I was able to run those literature cases successfully, and it required few minutes/seconds, but after 15 day I still have troubles with external flows (airfoils and wings).

Quote:
 Originally Posted by marcelorl (Post 463116) I am working on a labyrinth seal. My boundary conditions are pressure defined in the inlet and outlet. As I know it is very unstable boundary condition, I put zero gradiente for pressure in the inlet and changed the velocity until the pressure goes to 10 MPa.Outlet is pressure (8Mpa) defined and zero gradient for velocity. the velocity residual is ok, but the pressure is oscilating and i have tried everything that i could without success. Do you know anything that I can try? Thank you very much for the help.

 Linse November 25, 2013 10:24

Dear Marcelo,

fundamentally, it should be possible to use the results from simpleFoam also with rhoSimpleFoam.
BUT: Be aware that the solvers have different dimensions for the pressure field!
In general, in OF the incompressible solvers use p/rho, while the compressible solvers use p . Therefore you will have to think how to recalculate the pressure field for proper use within the compressible solver!

(Unfortunately I do not know about any tools or standard algorithms which can help you with that...)

 samiam1000 March 7, 2014 11:08

I am trying to use rhoSimpleFoam in order to simulate the flow over an airfoil.

I have many problem with convergence.

Have you ever done something like this?

Could you share a case, please?

Thanks a lot,
Samuele

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