When I was at the De-Havilland museum in St. Albans they had a few engines there and I couldn't resist trying to turn a Ghost (centrifugal flow) engine.
I was surprised but it wasn't actually that hard to move.
I could tell that there was a lot of inertia to overcome but once turning (even slowly) it was easy to spin faster.
Id imagine that the front bypass fans of some smaller jet engines are easier to turn (less inertia and weight because they are axial and not centrifugal).
Hope it helps.
btw, I tried the Gyron engine and had no chance of turning that engine !
hmm, I wonder if someone could manually turn the front fan of a RR Trent..... probably not