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Old   February 28, 2006, 11:23
Default help vof model
  #1
samy
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Hi, i am doing a simulation of water fall under the effect of gravity in a cylinder (water+ air, laminar flow). I chose the V.O.F model but i can't get a convergence result for my simulation. I have tried to modify the parameters inside fluent but the results still bad. ANYONE CAN HELP ME PLEASE
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Old   February 28, 2006, 18:16
Default Re: help vof model
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fred
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What are the boundary conditions u r using at outlet, what is your crieteria for Reynolds number calculation? before deciding laminar case, make sure it is not turbulent. Also in the VOF enabling panel activate body weighted average, since your flow is strongly dependent upon gravity. refarance pressure location in operating condition should be such tht it shuld always act on the lighter phase (in your case oil). Hope this helps.
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Old   February 28, 2006, 18:29
Default Re: help vof model
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Dustin
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Don't use outflow for a boundary Use a small time step, check the Cr # (should be .25) against your grid size and a decent estimate of what your flow velocity will be.

Good luck -D
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Old   March 1, 2006, 04:18
Default Re: help vof model
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smwang
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hi I have just finished an engineering work using vof model recently. An advice for you ,you must read the fluent help book firstly and do the corresponding example about vof model.

I want to say some about your question by my experience. first, a parameter of vof (ie the corrunt nmber) is the key.It confine the time step and influence result converge strongly . Now for laminar flow ,you can use 0.6"0.8 for it .

vof model is mainly for unsteady flow situation ,the result converge depends on every out iterations. if you do steady case ,the free surface level must be careful. if you have any question ,please mail me . wish you good luck.
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Old   March 1, 2006, 05:10
Default Re: help vof model
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samy
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I have 2 phases: water and air for the boundry conditions: inlet(water): velocity-inlet (0.1m/s, d=0.013 m), outlet (water): outflow, inplet(air): pressure-inlet, Model: Space:2D, Time: Unsteady, 1st-order, implicit, viscous: laminar, thank you

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Old   March 1, 2006, 05:43
Default Re: help vof model
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edi
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Change your outflow BC to a pressure or velocity boundary.

Hope this helps

Edi.
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