Fluid Mechanics and Thermodynamics of Turbomachinery, 5e

296 Fluid Mechanics, Thermodynamics of Turbomachinery
FIG. 9.4. Six-jet vertical shaft Pelton turbine, horizontal section. Power rating
174.4MW, runner diameter 4.1m, speed 300rev/min, head 587m. (Courtesy Sulzer
Hydro Ltd., Zurich.)
Nozzle
U
c 1
w 1
w 2
U
c 2
Direction of
blade motion
FIG. 9.5. The Pelton wheel showing the jet impinging onto a bucket and the relative
and absolute velocities of the flow (only one half of the emergent velocity diagram is
shown).
The effect of friction on the fluid flowing inside the bucket will cause the relative
velocity at outlet to be less than the value at inlet. Writing w 2 = kw1, where k < 1, then
(9.2)
An efficiency hR for the runner can be defined as the specific work done DW divided
by the incoming kinetic energy, i.e.
b 2