More RPM is needed than real test for a same thrust.

Hi I'm simulating rotating propeller in duct shroud. (external/rotating region/16000RPM/below mach1)

What I found was when I want to make same thrust as real test I need more RPM of... about 150% of real test.(after very sufficient 18travel and 1500iteration.)

every stream line and pressure contour is plausable..

I make every prop and parts very pricisely with SW.

Would it be there any mistakes in my test? or is it just inevitable gap between computer vs real situation..??

I should try internal analysis?

One more question.

When a stream of air flows through one face of computational domain(from outside of domain to inside), what is their boundary condition? Does Flow Simulation just calculate domain's outside as infinite air space?

Thanks for helping me.

By the way if you need files I'll attatch it (Now I'm in my working place )

SolidworksFlow Simulation