Hope you are doing good.
In cases such as yours if you wants to specify velocity-inlet to internal zones. For example, let’s say we have a cylinder completely inside the a box. Assume that the inside of the cylinder is meshed and have cell zone fluid-1, and outside of the cylinder is meshed with cell zone fluid-2. The inlet and outlet of the pipe is an interior type and are named interior-5, and interior-6, respectively. There is node-connectivity between fluid-1 and fluid-2 at all the boundary zones of the pipe. We know the velocity of the fluid entering.
In such a case, to specify velocity inlet to the pipe and make the fluid inside the pipe exit the domain at the outlet, follow the following procedure to accomplish this:
1. Define -> Boundary Condition. Select interior-5 under Zone and select wall on the right column under Type. Click on Yes to change the type. Two internal walls will be created, wall-5 and wall-5-shadow. ID of wall-5 will be the same as the ID of interior-5. These two new walls will be coupled by default and the available types for them are fan, interior, porous-jump, radiator, and wall.
2. A velocity-inlet type for an internal wall does not exist. In order to have types that can be applied on external zones, they need to be split. How to split wall-5 from wall-5-shadow? In the text user interface (TUI), type: /grid/modify-zones/slit-face-zone wall-5. Two additional walls will be created: wall-5, and another wall-###. A message will print on the cortex window which displays which zone is wall-###. These are now two external zones, one is adjacent to fluid-1 and the other is facing fluid-2. To have the fluid entering the pipe, the one which is adjacent to fluid-1 needs to be changed to velocity-inlet type. To find which one is adjacent to fluid-1, you need to visit the boundary condition panel for that zone and look under 'Adjacent Cell Zone'.
3. Repeat the above procedure to apply pressure-outlet if that is also an internal boundary.
Hope this helps!