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VOF(water-air)

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Old   December 24, 2005, 06:18
Default VOF(water-air)
  #1
yavuz
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Hello,

I am modeling(fluent 6.0) a flow which water enters into a vessel that is fully filled with air at the beginnig .I am using VOF multiphase model. But I always get an error message "turbulent viscosity is limited to...". To fix this error I decrease the density of the water to 50 kg/m3 and it works. I would like to learn the reason of this error whether because of the density ratio of water to air is high or grid skewness is not good enough.

thanks,

yavuz
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Old   December 25, 2005, 04:15
Default Re: VOF(water-air)
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nasser
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Its not Errore its an alarm Chek your boundary condition for Turbulence parameter
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Old   December 26, 2005, 05:54
Default Re: VOF(water-air)
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kharicha
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I agree that this results usually from a bad wall BC (check your y+). k could be badly estimated near the walls(area of high gradients) But it could also results from a too small number of grid points within the interface(also an area of high gradients). I was once using two phases with a densitw ratio of 3 only...and I got the same problem. The solution was to refine the mesh in the area where the interface was present. The refinement level was found to be proportional to the density ratio. Do the following: 1) create a mesh (coarse) in gambit 2) initialize the phase distribution in fluent.verify that the interface depth is two cells. 3) run few iteration to smouth the interface curve. 4) then refine the mesh (all the domain or ...)

now you should have 4 grid points within the interface.

then run your calculation and check the convergence of k and epsilon, verify that the turbulent viscosity ratio does not reach creazy results. Do (3-4) until you get correct results.

But DO NOT FORGET TO VERIFY YOUR WALL turbulence BC.

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