Originally Posted by chornedsnorkack
... what is the direction of the torque created by a turbofan? The air passing the fan must spiral along the direction of rotation, as the fan is imparting speed on the air. But the bypass air moves some distance inside the bypass ducts, unlike the propwash of a turboprop, which is free to spiral around the engine core... then the air entering the core is compressed by the compressor, which should make it continue spiralling. But then the core jet is slowed down by the turbine. Would it also be losing its torque in the turbine?
Don't forget, there is a row of fan stator vanes in the fan duct, downstream of the rotor. The intent of the stators is to stop the spiral vortex (swirl) imparted by the fan rotor, and in so doing convert that vortex energy to static pressure. (The passage between vanes acts as a diffuser) That's what gives the turbofan an advantage over the turboprop.
There's quite a bit of swirl at various spots within the core compressor and turbine, but not much by the time the gas exits the LP turbine. However, I think some CF6 models actually have some camber in the struts of the turbine frame, to recover the last bit of static pressure from the swirl.