[enginpower]

Hi all,
I'm studying a flow of water through a pipe where in some points the section area is very very small. All the pipe is long almost one meter, on the inlet section there is a pressure of 25bar and at the outlet section the pression drops to 1bar (atmospheric pressure). The pipe has a very strange shape, almost due to some control devices, so that in some points the section is almost like an annulus, but with the circles not concentric. In these points the minimum difference between the rays is almost 0.02 mm (2*10^-5m), while the inlet and outlet sections have an averaged diameter of 8cm (8*10^-2 m).
I need to simulate the entire flow in the pipe with a CFD software, but before I need to understand which phenomena occur, to take in consideration for the CFD simulations.

Obviously I thought to cavitation.

But because a very accurate mesh is necessary around the restriction, which requires so much memory, I would like to share with you suggestions for an accurate analysis, about the following questions.

How to consider the surface forces on the fluid, where the thin between the walls are only 0.02mm? What if fluid is gas? What if fluid is liquid? Do you know similar problems in literature to be useful to solve these fluid dynamics problems?

Thanks