Flowrate calculation error

Hi,

right now, I am running an internal FlowSim-Simulation, where the air circulates inside a bunch of parallel pipes and then coming back to the fan. I like to have the total flowrate through the fan and all the single flowrates inside the parallel pipes.

Of course, the total flowrate through the fan must be the sum of all the single flowrates. But the result shows, that there is a difference of round about 25% (the total flowrate through the fan is increased about 25 %).

I don`t see any net-failures and there is no "leckage".

So where is this different coming from?

My setup is quite simple: static pressure at the fan-area, and nothing else.

Goals: surface-goals of flowrate inside the parallel pipes and the fan-area. Global goals (min/max/average) of static pressure

Thanks in advance!

SolidworksFlow Simulation