I'm currently working on a school project where I'm trying to calculate the pressure drop between the inlet and outlet after water's been flowing for a while so that the inlet/outlet tanks are nearly full. The system's geometry is pretty simple: there're two cubic tanks and 8 cylindrical pipes running in between the tanks. The first tank has a circular opening for the inlet, and likewise, the second tank has a circular opening for the outlet.
So far, I've ran several different tests (all internal) by modifying geometries, time-dependencies, and some other features, and the pressure drop is higher than empirically measured.
The problem then, I think, is that the pressure drop is being calculated immediately after water flows through the first couple of pipes instead of it calculating pressure after the inlet tank fills up. Looking at the flow trajectories and particle studies, my idea seems to be supported.
So my question: Is there a way to find the pressure drop after the water in the tank reached a certain point? This point is basically when the water has been flowing long enough so that the flow in the pipes has become steady.