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-   -   Flotation of gasoil particules in water (https://www.cfd-online.com/Forums/fluent/41434-flotation-gasoil-particules-water.html)

 Alec June 19, 2006 08:03

Flotation of gasoil particules in water

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.

 Rajeev Kumar Singh June 20, 2006 01:15

Re: Flotation of gasoil particules in water

Check out, it seems you have not defined the direction of gravitational field in operating conditions panel

 Alec June 20, 2006 02:40

Re: Flotation of gasoil particules in water

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) ?

 Rajeev Kumar Singh June 20, 2006 03:02

Re: Flotation of gasoil particules in water

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.

 Alec June 20, 2006 04:33

Re: Flotation of gasoil particules in water

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 ?