The energy added to a stream of fluid flowing through the blades in a blade row:

${\displaystyle (h_{2}+u_{2}^{2}/2)-(h_{1}+u_{1}^{2}/2)=\omega (r_{2}v_{2}-r_{1}v_{1})}$

where

1 is upstream and 2 is downstream

ω is the rotor angular velocity

r is the distance from the axis of the stream tube upstream and downstream

v is the swirl (tangential) velocity component of the fluid velocity upstream and downstream

u is the impeller tip speed, which is defined as, u = (diameter in inches X RPM)/229.18