where L,D2 and A2 are length, diameter and cross-sectional area of
penstock, respectively. In addition, f is friction factor, Pk12 is the
sum of local losses in penstock due to entrance, bends, penstock
fittings and gates,AN is nozzle area at its exit (section3inFig. 1) and
kN is nozzle head loss coefficient, which is given by (e.g., [1]).