V w 1 {\displaystyle V_{w1}\,} and V w 2 {\displaystyle V_{w2}\,} are the swirl velocities at the inlet and outlet respectively. V r 1 {\displaystyle V_{r1}\,} and V r 2 {\displaystyle V_{r2}\,} are the blade-relative velocities at the inlet and outlet respectively. U {\displaystyle U\,} is the linear velocity of the blade. α {\displaystyle \alpha } is the guide vane angle and β {\displaystyle \beta } is the blade angle.