[immortality]

imagine we have very very huge reservoir that connects to a pipe and we want to analyze the flow in it.we know p and T at the reservoir and don't want to waste our valuable time to investigate flow at reservoir to find the velocity at outlet of it.on the other hand this reservoir is very huge and takes a lot of time analyzing it that even is useless for us because we want grasp only flow in the pipe.
Now the question is how we can set the boundary conditions at the inlet of the pipe that could precisely model what occurs in real world.
Your responce's and suggestions are appreciated.