I am trying to simulate hydrodynamics of a Venturi tube inserted into the vessel already filled with liquid to a certain height, while pumping the other liquid through the inlet. Above the initial level of liquid there should be air.

I tried two methods - first I wanted to create regions, mark them and then patch after initialization, as I saw in some tutorial. Strange things happened, so I am thinking about something else. First I sketched a line across the vessel in the place I want liquid-air interface and then I created two line bodies out of what is above line and below (and that line, to create closed loop). Then I created two surface bodies out of the edges, and wanted to make them a named selections in the meshing. Sadly, although I meshed them together, Fluent is detecting line between them as a wall (and I want it to be simply initial interface between them). What should I do to get rid of this wall between intended liquid and air zones?

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