Hi @asimon, This is because the simulation uses a rotating mesh zone in a steady state simulation. This applies rotational forces within the zone thus allowing it to be simulated as steady state. To simulate the blades actually rotating you will need to us an AMI for the rotating zone and simulate using a transient model. This is much more computationally expensive.
The advice is to first simulate a rotating steady state to ensure the setup is sound ad the mesh captures everything you need then run a transient simulation based upon the previous setup. Also, there is a good piece written in the documentation regarding this, much more detailed and accurate than my brief description above
hope this helps,