Large Viscosity multiphaseEulerFoam

kamakura117 · August 27, 2015, 18:13

Hello,

I am curious if anyone has experience modeling fluids with orders of magnitude different viscosities. When I have separation, I get unphysical velocities for droplets. The highly viscous fluid does not accelerate as would be expected. Lending me to believe that the fluid is unphysical as well. Is this outside the capabilities of this solver - or perhaps am I misunderstanding how the drag model work? Perhaps someone has a different experience and some advice?

Essentially, the problem is easily modeled by creating a drop of honey in air. The viscosity of honey is 10^7 times greater than air. In OpenFOAM, this drop will be suspended against gravity and not fall. The drag between the air and the honey is too great. I'm not very familiar with the multiphase approach to really understand what's going on...

arjun · August 27, 2015, 23:37

you will have problems doing this with commercial codes too.

If the viscosity ratio is this high, your matrix also has very high variation in coefficients (in similar ratios) to your viscosity. The AMG methods used in all these codes have very hard time converging on this. So this is usually difficult calculation.

Good luck.

kamakura117 · September 2, 2015, 18:30

Hmm, I see. I'll have to look into this. Are there any references you can point me to on this topic?

August 27, 2015, 18:13	Large Viscosity multiphaseEulerFoam	#1
kamakura117 New Member N/A Join Date: Jul 2010 Posts: 29 Rep Power: 15	Hello, I am curious if anyone has experience modeling fluids with orders of magnitude different viscosities. When I have separation, I get unphysical velocities for droplets. The highly viscous fluid does not accelerate as would be expected. Lending me to believe that the fluid is unphysical as well. Is this outside the capabilities of this solver - or perhaps am I misunderstanding how the drag model work? Perhaps someone has a different experience and some advice? Essentially, the problem is easily modeled by creating a drop of honey in air. The viscosity of honey is 10^7 times greater than air. In OpenFOAM, this drop will be suspended against gravity and not fall. The drag between the air and the honey is too great. I'm not very familiar with the multiphase approach to really understand what's going on... Last edited by kamakura117; August 27, 2015 at 19:35. Reason: Adding more information

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August 27, 2015, 23:37		#2
arjun Senior Member Arjun Join Date: Mar 2009 Location: Nurenberg, Germany Posts: 1,272 Rep Power: 34	you will have problems doing this with commercial codes too. If the viscosity ratio is this high, your matrix also has very high variation in coefficients (in similar ratios) to your viscosity. The AMG methods used in all these codes have very hard time converging on this. So this is usually difficult calculation. Good luck.

September 2, 2015, 18:30		#3
kamakura117 New Member N/A Join Date: Jul 2010 Posts: 29 Rep Power: 15	Hmm, I see. I'll have to look into this. Are there any references you can point me to on this topic?