Hi, everyone! I¡¯m modeling water-vapor flows through a converge-diverge nozzle using commercial code. For compressible flows, many commercial codes think the idea gas law is the appropriate density relationship. However, the water vapor I¡¯m using is 0.6Mpa, so in my opinion, it can¡¯t be thought as idea gas. Unfortunately, I couldn¡¯t find the UDF (User Defined Function) for density. Could anybody kind enough to give me some advices on how to set the physical properties. Anything about CFX,FLUENT or ANSYS is welcome! All thanks given to you for your help!

I can't understand your question very well. In fact , I think it's very easy.You can set the density of your water in command file of CFX4 and don't use the data in the database.

In CFX you can use the fortran routine USRDEN to set your density anyway you like.

P.Fonteijn

Which version of CFX are your using? If it is CFX 5 you have to use the general fluid model (density function of P & T) If CFX 4 then skip it because the latest information I had is that CFX 4 is not really well suitable for transonic flows.

Thank you for your help. I had found the UDF(user defined function) in FLUENT.(because i am more familiar with that code). Now my question is how can i decide the state of the fluid on the basis of the temperature which is equal to that of the saturated water-vapor?

If you have pure water vapor and no phase transition then you have a well defined equation of state (ideal gas with compressibility factor as a function of P & T). If you have phase transition (which you propably will have), you need to account for the latent heat which is large for water vapor. You might then neglect the volume of the liquid water. For further reference: look up the work of prof Schnerr in Karlsruhe or the work of Young in Oxford (or Cambrigde, I'm not sure) on condensing flows in steam turbines and Laval nozzles.

Bart Prast: Thanks for your concern!But how can i get the information of the work of prof Schnerr on condensing flows in steam turbines and Laval nozzles?

Go to his homepage (with references): http://www-ism.mach.uni-karlsruhe.de/

Thanks a lot!