In an axial flow compressor as used in modern jet engines, the goal of a compressor rotor is to increase the angular momentum of the air by imparting an increase in swirl velocity. (Note: the goal of an entire compressor stage, including rotor and stator, is to raise the pressure of air, but I'm focused purely on the rotor right now).
However, I'm a bit confused as to what imparts this increase in swirl velocity. Is it: a) the rotational motion of the rotors themselves? or b) the lift generating characteristics of the rotor airfoil shape.
Basically, I'm not sure why the blades of the rotor needs to be lift producing entities. It seems that if you had a flat plate it would also increase the rotational velocity to the flow because it itself is rotating. For example, in typical pictures of velocity triangles, nowhere is lift and or drag mentioned.
Hopefully that question makes sense!