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December 7, 2008, 03:01 
Singularity in two fluid model (EulerianEulerian)

#1 
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In the Eulerian twofluid model for twophase flows, the standard formulation for the momentum equations becomes singular as the volume fractions tend to zero. Some papers suggest that resulting velocities can fluctuate widely in the regions where volume fractions tend to vanish.
How do you deal with the problem of singularity in your code? Or could you give me some effective suggestions for the problem or references about EulerianEulerian Model? Thanks! 

December 8, 2008, 02:39 
Re: Singularity in two fluid model (EulerianEuler

#2 
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single phase or decoupled phase formulation is an effective method, you can get idea from immersed bc methods e.g. see: Hao & Prosperetti JCP 2004, or sharp interface cartesian method by S. H. Udaykumar in JCP
a commnet: you can use variable density formulation, e.g. rho = vol_frac * rho_flo + (1vol_frac) * rho_virtual ratio = rho_flow/rho_virtual ratio >> 1 

February 27, 2010, 06:35 

#3 
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Claus Meister
Join Date: Aug 2009
Location: Wiesbaden, Germany
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Hello vadim,
you said "velocities can fluctuate widely". Could it be that during the simulation the time steps becomes smaller and smaller. My question based on the a problem i have. My simulation runs between 0s and 0.6 s, and in time of 0.18s simulation time the time steps, which are dependent on CFL number (bounded by 0.5), getting smaller and smaller and evetnually the simulation abords. cheers, 

February 27, 2010, 06:36 

#4 
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Claus Meister
Join Date: Aug 2009
Location: Wiesbaden, Germany
Posts: 241
Rep Power: 11 
Furthermore, should our problems be related then I want changes my question: how can i avoid it?


February 28, 2010, 18:54 
reference

#5  
Senior Member

Hi there,
Could you kindly post your reference where they indicate as alpha > 0, vel > high values? Thanks, CFDtoy Quote:
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