[yanqoue]

Hello, I have a solution that I'm not sure if it's exactly true, that's why I wanted to hear your opinion as well.

I tried to simplified the problem for you (see the picture).

You can think of this shape as a 3D pipe with two horn like channel on the side. There is one inlet and several small circular outlets. My expectation was that most of the incoming liquid will be going through the center and leaving the domain, whereas some portion of it will be circulating inside these side channels. But when I checked the results, streamlines were similar to what I shown on the sketch. Not a single streamline was going inside the channel.

Like, I know this seems logical on one side, but, like no movement through the channels? No disturbance caused by these side channels? Does this seem logical to you? How do you explain this?

[Gert-Jan]

Why do you use streamlines from inlet to outlet?

If you want to see what is going on in those corners, make a cross section through these corners and look at the velocity and vectors.
Alternatively, make a small cross section solely in these corners (by limiting the large one with a rectangular or circular shape) and start streamlines from that small cross sections. Use forward and backward. It will show how fluid is going towards the corner and where flows to afterwards.

[Opaque]

Have you plotted the pressure contours?

You are assuming the expansion will create a recirculating bubble before reaching the expanded section downstream. The bubble may be there but not as intense as you expect and the streamlines will not show it if the value is too small for the range covered, i.e. those streamlines may be below the lowest value in your range. Are you using conservative/hybrid values?

I would expect the fluid in the two small cavities to barely move if anything at all. It is all dependent on your flow conditions.

[karachun]

You can check mass/volume flow at central and side pites. This is more convinient method than counting streamlines.