It is important to understand that the fluid solve is like a tank of incompressible water. If you push it swirls around the push and does not behave like simple particle flow. Motions towards or away from a point are not possible as these would involve compression.
Also you can directly paint velocities on the fluid without needing a 2d fluid. These set the initial state, although if you want you could make the velocity grid static, in which case it would be a simple steady state flow.
At any rate one could also use a 2D fluid as a force on a 3D one. Create a 2d fluid and make its velocity grid static (the density grid can also be turned off ), then paint some velocity into the fluid. Now create a 3d fluid with an emitter and set the 2d fluid as a field for the 3d one in the dynamics relationship editor. The 2d fluid by default is nearly flat. Make its boundary draw "bounding box" and increase the size Z value to thicken it, so it can influence more of the 3D fluid. One could use this to define a fixed flow path for the 3D fluid while still allowing it to have a dynamic velocity grid. Note that one could also use a 3D fluid with painted 3D velocity as a force on a second 3D fluid.
Duncan