3. Torque and overall forces in a rotor

Due to the symmetry of the moving channels around the axis of rotation OO′, the forces exerted by the rotor on the fluid reduce, in the general case of total injection and neglecting the effects of instationarity, to :

• a resultant moment about the OO′ axis, called torque, knowledge of which is essential since its work is identified with the energy exchanged between the fluid and the rotor ;

• a resultant carried by OO′ whose reaction, applied to the rotor, is called thrust. This force plays an important role in the design of turbomachinery, as special measures must be taken to counteract it and keep the rotor in a fixed position in the axial direction. These consist firstly in reducing thrust by acting on the geometric shape of the rotor (a balancing operation), and secondly in supporting the residual thrust...