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-   -   Free Surface Modelling and Reversed Flow Error (http://www.cfd-online.com/Forums/fluent/34374-free-surface-modelling-reversed-flow-error.html)

Javier González August 10, 2004 11:43

Free Surface Modelling and Reversed Flow Error
 
Hi, I'm a new user of Fluent. i'm trying to model a 2d rectangular tank with a free surface. I have read that the VOF model is used for tracking a free-surface, but that is not my case. I have used a pressure outlet boundary condition in the top of the tank, but an error appears showing that there is reversed flow in a given number of faces. I have read that the apropriate boundary condition to be used is a symetry boundary.

Does Anyone know why, and if is this correct?

Thanks in advance Javier

Raphael August 11, 2004 07:23

Re: Free Surface Modelling and Reversed Flow Error
 
What type of flow are you modelising? Where are the inlet and the outlet? I am currently doing the same (tank, VOF..) with a velocity inlet and a pressure outlet for the vertical sides, and symmetry for the top and the bottom. It works, so I could help you if it was the same...

Raphael

Javier González August 11, 2004 15:30

Re: Free Surface Modelling and Reversed Flow Error
 
The inlets and aoutlets are microjets placed at the bottom. The top of the tank is the free surface. I try the symetry boundary at the top and it works good, but i will try with VOF to see how it is altered.

Thanks for your help, and feel free to email me for anything related to the modelation.

Best regards. Javier

Raphael August 13, 2004 12:53

Re: Free Surface Modelling and Reversed Flow Error
 
Have you ticked the box "specified operating density" in the operating conditions panel? I had problems with hydrostatic pressure in the light phase, above the surface, with important pressure variations, and a disturbace of the flow. As soon as I ticked this box, problems were solved, and hydrostatic pressure was OK.

Hope this helps.

Raphael

Javier González August 16, 2004 11:37

Re: Free Surface Modelling and Reversed Flow Error
 
Yes, I have done that, But now appears another error when i'm running the VOF. It says:

"Turbulent Viscosity limited to turbulent viscosity ratio of 1.000000e+05 in 8 cells"

In the plot of the residuals one can see how the grow in time (not all, but someones).

I had to change the pressure inlet zone type for the upper boundary to a symmetry boundary to avoid the reversed flow error. I have reduced the under-relaxation factors for al ecuations. But I can't control the break down of the model.

Best Regards, Javier.



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