Flow through axial-flow turbo machine rotors can often be assumed axisymmetric i.e. velocity components do not change around the rotor circumference either at inlet or at outlet. Not strictly true as wakes formed behind rotor blades(and inlet guide vanes) which sometimes cannot be ignored. be ignored.

Flow through a rotor, affected both by theinter blade passage geometry and the rotorgeometry Rotation can always be expressed by geometry. Rotation can always be expressed by 3 velocity components:

(i) fluid absolute velocity V

(ii) fluid velocity relative torotor w

(iii) rotor circumferential velocity U