9 Hydraulic Turbines
324
provided to supply air, as air is entrained in the draught tube. Cross-flow turbines
can be constructed very easily, but their efficiency is significantly lower than that of
other hydraulic turbine types, namely about 80 % compared to about 90 %.
9.3 Pelton Turbines: Impulse Turbines
9.3.1 Performance Characteristics
Figure 9.6 sketches the flow over the rotor buckets of a Pelton turbine (the term
bucket is typically used).
The inlet velocity v 1 has the same direction as the blade speed u:
The top angle of the central ridge of the bucket does not equal zero, generating a
small incidence component at the rotor inlet. The incidence loss is integrated in the
w v u
1
1
= − .
Fig. 9.6 Flow over a Pelton turbine bucket
Fig. 9.5 Cross-flow turbine
324
provided to supply air, as air is entrained in the draught tube. Cross-flow turbines
can be constructed very easily, but their efficiency is significantly lower than that of
other hydraulic turbine types, namely about 80 % compared to about 90 %.
9.3 Pelton Turbines: Impulse Turbines
9.3.1 Performance Characteristics
Figure 9.6 sketches the flow over the rotor buckets of a Pelton turbine (the term
bucket is typically used).
The inlet velocity v 1 has the same direction as the blade speed u:
The top angle of the central ridge of the bucket does not equal zero, generating a
small incidence component at the rotor inlet. The incidence loss is integrated in the
w v u
1
1
= − .
Fig. 9.6 Flow over a Pelton turbine bucket
Fig. 9.5 Cross-flow turbine