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kuhbuh July 24, 2009 05:17

supersonic two phase inlet

I'm modeling compressible high-speed two-phase flow in CFX. My inlet is supersonic based on the two-phase sound speed. But, when I consider the individual sound speed of each phase at the given pressure and temperature, both phases are subsonic. Which criteria does CFX use? I believe it's the indivindual sound speed because of "mixed" options in CFX but I want to confirm it. Please enlighten me. Thanks a lot!

kuhbuh July 28, 2009 10:07

guys help me with this question PLEASE!!! Thanks a lot!

ghorrocks July 28, 2009 20:21

This is quite a specialised question so it does not surprise me you have not got an answer. It is not in my area of expertise so I would be reading the documentation and not speaking from experience. You will have to read the documentation and work it out, or contact CFX support for more detailed assistance.

kuhbuh July 29, 2009 01:13

Thank you so much Sir Glenn!
I've read the documentation several times but I could not find specific explanation for this. I've just thought that having an "inlet(mixed subsonic-supersonic)" option for two-phase model in CFX means that the criteria of being "supersonic" or "subsonic" is on per phase basis. Our support is in Japanese that's why I usually rely on this forum. Thanks again sir!!!

ghorrocks July 29, 2009 01:18


No, you misunderstand the mixed inlet. It means some regions of the inlet can be subsonic and some supersonic. It does not mean that at a particular point the flow can be both sub and super sonic for different phases.

In fact I think the sub/super sonic at a point you mention is impossible as the pressure field is shared between phases so pressure waves must propagate at the same speed for all phases. So the speed of sound must be the multiphase value.

Glenn Horrocks

kuhbuh July 29, 2009 01:48

Sir Glenn,
Thank you so much!!!
I missed that concept about sharing a common pressure field. You've explained it very well. Thanks again!

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