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-   -   About the multiphase flow (http://www.cfd-online.com/Forums/fluent/49273-about-multiphase-flow.html)

Xue September 16, 2008 07:23

About the multiphase flow
 
Hallo,

I am puzzled about the multiphase flow. Does the multiphase model can be used in steady flow?

I tried to simulate a case with the mixture model or Eular model for the system air and water (the case looks like the bubble flow), I would like to see how much air are mixtured into the water when it comes to the steady state. Therefore, I treated it as a steady flow. However, there is always a error information below and the simulation can not go on in 100 iterations: turbulent viscosity limited to viscosity ratio of 1e5.

However, if I changed it into unsteady state, the information above only exists in several time steps and disappear after a short time.

Does somebody can tell me, whatis the reason for that? Does it mean that the multiphase model can not be simulated in steady state?

thanks a lot

xue

Xue September 17, 2008 04:03

Re: About the multiphase flow
 
Is there anybody who can give me some suggestions?

Thank you very much!

xue

bashu September 17, 2008 10:30

Re: About the multiphase flow
 
Have you tried transient to see if you can run your model? Normally large density differences can not be run steady state. So run transient and after you reach a quasi-steady flow you can turn the time-averaging feature in fluent and look at the time average results.

Xue September 17, 2008 21:14

Re: About the multiphase flow
 
Hi, Bashu,

Thank you very much for your kindly reply. I have tried, it can work in transient. Could you tell me the reason that we can not run it in steady state for the large density differences system?

Thanks again!

xue

bashu September 19, 2008 13:05

Re: About the multiphase flow
 
Just to make it clear it is not just the density difference that's important. You have the volume fraction effect as well. In other words for a dilute system (<2%) you should be able to have a steady flow regardless of density difference. The multiphase is normally transient since the time scales of the two phases are much different and so they won't flow together.


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