How to: define fluid-fluid boundaries as 'wall'
My case set-up is the following: I have 3 fluid domains. 1) the smallest, inner tube (representing a simplified catheter), 2) the outer tube surrounding the catheter, and 3) the rest of the geometry, where the two tubes have merged. What I want to model is that fluid flows in from both the inlets of "1" and "2" and then start to mix when they have reached "3".
What I used to do is use mesh interfaces to define the contact regions between the three domains and set the appropriate conditions. Now that I've switched to Fluent Meshing for my meshing and use the "Share Topology" option, that doesn't seem to do the trick anymore.
What I've tried is I've defined both the contact region between "1" and "2" (i.e. the 'wall' of the inner tube), and the contact regions between "1"/"2" and "3" (i.e. the outlets of "1"/"2" and the inlet of "3") as 'interior', because they're fluid-fluid boundaries. However, there is a distinct difference between these types of boundaries: the region between "1" and "2" should be treated as a wall (no mixing), while the region between "1"/"2" should just allow the fluid to pass as if the contact region isn't there. My question is now: how do I define that?
Using just default 'interior' setting, I get this. However, I'm not sure if this is what I need. As the catheter wall is 'real', the fluid should slow down to 0 velocity at that wall, but that doesn't seem to be happening (which makes sense, because I didn't model it that way. Also: I defined the catheter inflow much larger than the rest of the inflow, and it does seem like the catheter flow is slowing down, which also shouldn't happen because the 2 regions should be separated.
I would be very grateful for any advice!