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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?


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!


pilar January 14, 2004 08:28

Re: BC for free surface

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?


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.


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