Thanks for your answer,
I don't think I fully understand your answer. The simulation is transient, and I am utilizing dynamic mesh motion as well. The true geometry I refer to has this type of geometry. Pressure inlet of 210 bar is unchangable as well as pressure outlet ports of 0 bar. Narrow point you mention is actually a wall in the real geometry. To do the analysis without having any problems at the beginning, I simply remove the touch of the two walls which are coinciding in one point and replace the whole region with small meshed region so the fluid can flow.