out flow problem
 

I got some problems in my case, first, simplify my case to Part A and Part B, I want to specify the flow at the outlet of Part A, then I use the mass flow outlet boundary condition, the result is shown in the first picture, I think the flow that I set mass flow outlet didn't pass to Part B. What I want is like the second picture shown.

Should I use another boundary condition there or is there another way I can use to specify the flow rate at that location?

https://i.imgur.com/VeJDJY1.jpg

https://i.imgur.com/NhzbrvA.jpg