I'm doing a simulation of transonic flow through a nozzle. I would like to know the typical setting needed in AVL FIRE v8.2 for such a simulation. I have convergence for a combination of mass flow and pressure boundaries, but find it hard to achieve convergence for total/stagnation pressure as inlet and static pressure as outlet boundaries. I can only achieve convergence for very small inlet and outlet pressure differences, i.e. only for subsonic flow.

What would be the first thing I should do?

I have activated all the equations: momentum & energy. However I am unsure about compressibility options in AVL Fire. At the moment I am using compressible. Which between compressible and supersonic is the better choice?

What order of under-relaxation factors are typical to achieve convergence for transonic flow?

BTW, the nozzle I'm simulating is very small, about 3mm in diameter.

Is there a recommended differencing scheme & linear solver for transonic flows/this type of problem? I seem to remember MARS to work for some transonic simulations in Star-CD (is this correct?), does anyone know which of the schemes offered in AVL is similar to MARS?

Finally, is it possible for Fire to have a boundary surface which is sonic/supersonic? I know this is not good practise for Star-CD.

I'm new to CFD, so any insight(s) however small may be of help.

Thanks.

[mohsenfjs]

hi

i'm doing some simulations in the same field as you do so if you are interested to share ideas over this send me an email on mohsen1_khalafi@yahoo.com

thanks a lot