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Flotation of gasoil particules in water

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Old   June 19, 2006, 08:03
Default Flotation of gasoil particules in water
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Alec
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Hi,

I have troubles with simulating particules of oil or gasoil. I'm using the VOF model to simulate a 3D box with 2/3 of water and 1/3 of air a the top of the box. I'd like to check if the behavior of gasoil particules is similar to the theory of Stokes.

There's no flow in the box and I'm injecting the particules without any initial velocity by the bottom surface of the tank. They should have a positive velocity in the vertical direction but my first simulation show that the particule just spread on the bottom not going up at all !

It's gasoil in water !

I tried injecting the particules in the middle of the water and they seemed to go up and down randomly.

I've not the slightest idea of where the problem is.

Thanks in advance.
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Old   June 20, 2006, 01:15
Default Re: Flotation of gasoil particules in water
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Rajeev Kumar Singh
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Check out, it seems you have not defined the direction of gravitational field in operating conditions panel
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Old   June 20, 2006, 02:40
Default Re: Flotation of gasoil particules in water
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Alec
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The problem is I've already check this and it's correct ! I've chosen -9.81m/sē in the Z direction (that's how I created the tank) so this should works.

I've check many things (scale, injection, operating conditions, boundary conditions, etc.) and I can't see where the problem is.

My boss said that it could come from the fact that the particules can't go from and cell to another because from one time step to another, their speed is not sufficient.

And don't know if it could be the problem. Is there a limit in the size of particules (for instance they can't be bigger thant a cell) ?
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Old   June 20, 2006, 03:02
Default Re: Flotation of gasoil particules in water
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Rajeev Kumar Singh
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Speed can be one factor, so may be you should run it for some few seconds of cycle. Also check what is the density difference and calculate what should be the terminal velocity.
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Old   June 20, 2006, 04:33
Default Re: Flotation of gasoil particules in water
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Alec
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I've already calculated the velocity and the particules are not moving from a cell to another in the vertical direction.

So you think that it could come from that ?

In this case there is another issue as the particules are spreading horizontaly. Is that logical without any flow ?

(Thanks for your help !)
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Old   June 20, 2006, 04:51
Default Re: Flotation of gasoil particules in water
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Rajeev Kumar Singh
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For a moment increase the diameter of particle (use only one) and simulate a simple 2d test case.
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