is there difference b/w moving object in a fluid and static object in a moving fluid?
That's called Galilean invariance. There's no difference whatsoever between a steadily moving object in a stationary fluid, and a stationary object in a steadily moving fluid.

You seem to be thinking that in a wind tunnel, some air will always get trapped downstream of (that is, behind) the object; and that for an object flying outdoors, air will never get trapped behind (that is, downstream of) the object. Neither of those things is true.

I see that you're thinking about supersonic flight; you're saying that


it seems like if an object is flying supersonically, it will leave a vacuum in its wake, but
it also seems like if an object is stationary in a supersonic wind tunnel, it will not have a vacuum in its wake. 


I actually agree with your intuition here; I also think it seems like these two things will happen. 

But when my intuition contradicts a law of physics, it doesn't mean that the law of physics is wrong; it means that my intuition is wrong.