Selecting a rotating region - SolidWorks Flow Simulation

Hello !

I would like to study the flow around a rotating part and its axis.

To make things simple, I have made a assembly composed of two parts : the axis and the rotor, which is, of course my rotating part. I would like to designate this part as my rotating region.

But for some reasons I can't select it. When I am going to

As a result, I can't run a simulation to know the flow around my system...

Can someone help me ?

Please find attached some screenshots of my system.

The axis and the rotor :

Making sure rotation is selected :

I can't click on "rotor" to select it as a rotating region:

Thanks a lot !

SolidworksFlow Simulation