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-   -   BC for free surface (http://www.cfd-online.com/Forums/fluent/32838-bc-free-surface.html)

pilar January 13, 2004 10:35

BC for free surface
 
Hi, I'm modelling a 2D rectangular opened reservoir (that is, in contact with the atmosphere) with water. It only has an entry, an exit and the rectangle is closed by means of a line that represents the free surface, the surface wich is in contact with the atmosphere. I have used these boundary conditions:

Velocity inlet for the entry.

Outflow for the exit.

Pressure inlet for the free surface (with pressure = 0)

I want to obtain the path lines and they should be parallel to the free surface, that is, horizontal lines. But I obtain vertical lines near this surface so it seems that some flow is entering throught it but in 'report fluxes' I obtain that the mass flow rate entering is 0. I think that I must change the boundary condition of the free surface , is it correct? What BC can I use?

Thanks

DAE January 14, 2004 08:06

Re: BC for free surface
 
I assume you have used a wall to model the free surface?

If so, have you specified the shear to be zero?

If not, then you will have boundary layer effects!

DAE

pilar January 14, 2004 08:28

Re: BC for free surface
 
hi,

If I use 'wall' as boundary condition for the free surface, path lines are ok. But pressure is not the atmospheric pressure!!! Maybe it's a good solution but I'm not sure because of this different pressure.What do you think?

Thanks

DAE January 14, 2004 08:36

Re: BC for free surface
 
Why do you want the atmospheric pressure...

To obtain a pressure profile for hydrostaic pressure i.e. rho.g.h ?

If that is all you may as well ignore it and use a custom field function for hydrostatic pressure.

DAE


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