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-   -   Compressibility In The Cavity Region In Cavitation (http://www.cfd-online.com/Forums/fluent/31803-compressibility-cavity-region-cavitation.html)

Roozbeh July 10, 2003 09:03

Compressibility In The Cavity Region In Cavitation
 
Hi all; I want to model cavitation with the cavitation option of Fluent. In the cavitation , the compressibility of the cavity region ,is very important. Have anyone used the cavitation option of Fluent6.012 and set the fluid in the cavity region compressible? I did this , but I did not see any convergency. I think my problem is about inlet B.C. I have used velosity inlet B.C.


mateus July 11, 2003 01:27

Re: Compressibility In The Cavity Region In Cavita
 
Hi Roozbeh!

Long time since you were here...

Hm copressibility in cavitation. You are right, the sound speed in mixture of vapour-liquid phase can be as low as 20m/s, so it's very important to model that. Im not shure what you did. Did you just set one phase as compressible or did you make some kind of udf for mixture compressibility? If you did the first (set compressible vapour) you did't do much - it doesn't really influence the cavitation. I tried this also but had bad stabillity even with pressure or mass flow inlet b.c. If you made an udf for mixture compressibility (and if it works - even if it works very bad) you are probabilly the first to do it in Fluent. This is he same thing that Reboud Coutier and Delagosha did with their barotropic cavitation model (relate fluid density to pressure) - it's still the best way to model cavitation by my opinion.

You also have to know that most simulations ommit problem of compressibility (at least those who describe cavitation with models based on bubble dynamics equations).

Are you now using your own model (based on VOF - did you succed) or the original fluent model?

best regards MATEUS

roozbeh July 12, 2003 02:02

Re: Compressibility In The Cavity Region In Cavita
 
Hi Mateus; Why for the mixture? I think that I should to model only vapor as a compressible fluid.Please describe foe me if you know more!

A problem that I encountered some month ago, is that in Fluent UDF , the density can only be a function of temprature or distance. Can I write a UDF in which density is a function of pressure or volume fraction? You know? Can you send me or describe more about Coutier's barotropic model? thanks .


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