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Water/Mud Problem - Multiphase

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Old   July 27, 2004, 08:04
Default Water/Mud Problem - Multiphase
  #1
James Date
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Hi

Although I've had quite a lot of experience modelling single phase flows using CFD, I would like to know how easy it would be to set up a multi-phase flow problem in Fluent.

My problem is:

1) A simple square tank with an outlet pipe on the top. 2) A inlet water pipe on one of the side walls above the mud layer, i.e. only sucking water in. 3) A mud layer on the bottom of the tank. 4) Water filling the rest of the tank above the mud..

Basically (this might be a bit of an understatement!) would like see under what conditions the mud might get sucked up and out of the outlet.

My questions are:

1) What Fluent model to use i.e. VOF? 2) Are there specific grid generation issue's I need to consider above making the grid refined enough in the water/mud interface region. 3) Do you need to initialise the flow domain i.e. set the mud water level before the simulation takes place? 4) Approx. solution time for a 500000 cell problem? 5) What are the major problems and pitfalls of solving such problems?

Regards James
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Old   July 27, 2004, 12:31
Default Re: Water/Mud Problem - Multiphase
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laika
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hi,

for this one I'd use the mixture model. It's fast, very stable and good. Just play around with the model activated and you will see how it is used. But try on a smaller mesh first. Why do have so many cells?

Don't forget to activate gravity and the 'boudy force weighted'.

For initialisation, you patch a mud fraction to a certain region. Is there a mud inlet somewere? Is inlet-flow containing any mud?

good luck!

Laika, still orbiting
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Old   July 27, 2004, 14:31
Default Re: Water/Mud Problem - Multiphase
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James Date
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Hi

Thanks ever so much for you advice.

So why use the mixture model, is it better than the VOF method or does it use a similar approach?

My prob will prob have less cells in to begin with.

The mud will not flow in from anywhere.

James
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Old   July 28, 2004, 04:00
Default Re: Water/Mud Problem - Multiphase
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laika
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ith VOF, Fluent assumes the liquids mud and water are immiscible. Therefore he has to track the interface-location. That's not really true with mud. You only want to have a mud-content in each cell. They can mix a bit, as will be the case when the mud is going through the outlet, and the mud can precipitate due to gravity in calm zones.

The mud-phase will have significant higher viscosity than the water. Fluent will use a weighted averadge for cells containing both phases.

good luck,

Laika, still orbiting
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