CFD Online Discussion Forums

CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   CFX (http://www.cfd-online.com/Forums/cfx/)
-   -   Multiphase convergence problem (http://www.cfd-online.com/Forums/cfx/75226-multiphase-convergence-problem.html)

delaneyluke April 20, 2010 02:26

Multiphase convergence problem
 
Hi,
I'm running a liquid-gas multiphase problem with liquid as the continuous phase. I need to anlayse over a range of properties (constant) of the liquid phase. With a low viscosity (10 centipoise) i have no problems. The problem begins when i increase the viscosity to 500 cP and 1000 cP. The momentum imbalances fluctuate a lot (10-20%). I've even tried running the case as laminar (considering the higher viscosity) with the same problem.

Any suggestions.

Luke

ghorrocks April 20, 2010 07:38

Hopefully there is a physical explanation for it - but I can't think of one. You would have to give more details about what you are modelling.

Does some transition happen as the viscosity goes up? Maybe the bubble go from spherical cap to spherical regimes and you are using an inappropriate drag model which gives wrong drag numbers and leads to instability.

delaneyluke April 21, 2010 00:25

Thanks Glen,
But i tried modeling the flow as single phase (laminar, with 1000 Cp viscosity) and arrived at the same fluctuating imbalances. This is as simple as you can get. Constant property fluid, laminar flow .. i dont get why it's so tough to converge. The inlet velocity is 9.84 m/s and domain pressure 10 bar.

ghorrocks April 21, 2010 18:54

I repeat - does some transition happen? Maybe you go from the spherical cap regime to spherical and your drag model is not appropriate any more.

Nothing is "simple" when you are talking multiphase flow.


All times are GMT -4. The time now is 07:29.