Learning Forum

[shadowfax7]

Hi all

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".

[DrAmine]

Then define the boundary as wall instead of interior. If the mesh is conform Fluent will create wall/wall-shadow. If not conform then you can create interfaces with side 1 and side 2. Even in your current setup you can try to transform the interior 2d boundary to wall. Have you tried that? (also avoid talking about 1 , 2 and 3 if they are mentioned in screenshots..)n

[shadowfax7]

Thanks for this advice. nHowever, when I define the boundary as 'wall', and I run a simulation with 2 different phases in the smaller tabe and the outer tube, I see they're already mixing before the point where the two tubes come together - which shouldn't happen. I don't understand why this is happening. nn

[Rob]

Are you seeing wall and wall:shadow? Why are you using phases if the fluids are mixing? We use species for that, and if you don't turn on the reactions they just mix. n

[DrAmine]

Is it really a wall? Can you you show boundary condition secreenshot? Also the screenshot of the inlet condition (left side in the picture) and the mesh of it.n

[shadowfax7]

: yes, I can see wall and wall:shadow (name of the wall here is 'inlet-cath:solid:1'). As for the phases, I'm trying to model a catheter injection of saline in an artery filled with blood. I'm using the VOF model - you think it's not appropriate? n: below you find a screenshot of the inner tube (meshed) and an outline of the outer tube, with the rest of the geometry meshed. For the inlet, I define a volume fraction of 1 for 'saline' for the inner tube, and a volume fraction of 1 for 'blood' for the outer tube.nn

[Rob]

As blood and saline mix you want to use species. If blood and saline didn't mix (eg oil and water) then VOF would be the correct choice. nAs an aside, blood is technically a slurry so I'd suggest some background reading into blood viscosity. n