biphasic model

enzome · November 10, 2011, 06:26

Hi, this is my 2 thread, I hope you can help me again.
I'm working on an anaerobic digester. I have to make a simulation with a biphasic model where are entering the 87% of sludge and the 13% of air from the same inlets. the inlets are 2 and they are on the bottom of the digester, the outlets are on the top and are 2 as well. I tried to make 2 simulation, one with VOF and another with multiphase segregated flow but both of them are diverging. Maybe I put the wrong boundary conditions, i tried to put the inlets as flow-split or velocity inlets, for the outlet flow-split or pressure outlets. I try to follow the tutorial of the Star manual setting the same models and parameters, obviously linked with my problem, but no convergence. If someone has got a suggestion please don't be shy

Thanks

willimanili · November 10, 2011, 08:43

I havent much experience with multiphase problems but i would suggest that you should read the section Modeling Multiphase Flow in the user guide. Especially about Phase Interactions and Eulerian Multiphase Model.

Maybe anyone else can give you more detailed help.

Have fun

abdul099 · November 11, 2011, 13:51

The most important question is: How do you judge convergence or divergence? A lot people are only looking on residuals and forget that residuals in Star-CCM+ are normalized.

For the "multiphase segregated flow" simulation (I think, it is an Eulerian multiphase, right?), consider that it tends to diverge when running turbulent. When you're running turbulent while your flow actually is laminar, switch of the turbulence model.
When it's turbulent, reduce under-relaxation factors to very low values, reduce time step size etc.

Ladnam · December 17, 2011, 14:22

Another tip when running turbulent segregated multiphase is to first run until convergence using the laminar model and then turn on turbulence.

November 10, 2011, 06:26	biphasic model	#1
enzome New Member vincenzo Join Date: Nov 2011 Posts: 3 Rep Power: 14	Hi, this is my 2 thread, I hope you can help me again. I'm working on an anaerobic digester. I have to make a simulation with a biphasic model where are entering the 87% of sludge and the 13% of air from the same inlets. the inlets are 2 and they are on the bottom of the digester, the outlets are on the top and are 2 as well. I tried to make 2 simulation, one with VOF and another with multiphase segregated flow but both of them are diverging. Maybe I put the wrong boundary conditions, i tried to put the inlets as flow-split or velocity inlets, for the outlet flow-split or pressure outlets. I try to follow the tutorial of the Star manual setting the same models and parameters, obviously linked with my problem, but no convergence. If someone has got a suggestion please don't be shy Thanks

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November 10, 2011, 08:43		#2
willimanili Member Join Date: Feb 2011 Location: DE-PB Posts: 56 Rep Power: 15	I havent much experience with multiphase problems but i would suggest that you should read the section Modeling Multiphase Flow in the user guide. Especially about Phase Interactions and Eulerian Multiphase Model. Maybe anyone else can give you more detailed help. Have fun

November 11, 2011, 13:51		#3
abdul099 Senior Member Join Date: Oct 2009 Location: Germany Posts: 636 Rep Power: 21	The most important question is: How do you judge convergence or divergence? A lot people are only looking on residuals and forget that residuals in Star-CCM+ are normalized. For the "multiphase segregated flow" simulation (I think, it is an Eulerian multiphase, right?), consider that it tends to diverge when running turbulent. When you're running turbulent while your flow actually is laminar, switch of the turbulence model. When it's turbulent, reduce under-relaxation factors to very low values, reduce time step size etc.

December 17, 2011, 14:22		#4
Ladnam Member Join Date: May 2010 Posts: 40 Rep Power: 15	Another tip when running turbulent segregated multiphase is to first run until convergence using the laminar model and then turn on turbulence.