2
1 Working Principles
Examples of power receiving machines are:
•  incompressible fluid (water, oil), dominantly a pressure increase: pump
•  compressible fluid (air, gas, vapour)
−  high pressure increase: compressor
−  low pressure increase (especially with air): fan (puts air into motion).
1.2 Examples of Axial Turbomachines
We consider two examples with water: a hydraulic turbine and a pump.
1.2.1 Axial Hydraulic Turbine
Figure 1.1 sketches a longitudinal section of a small hydraulic turbine. In the flow
sense, the machine consists of three components: a stator part, encompassing an inlet
and a guide ring, a rotor (runner) and a stationary diverging pipe. Both the guide ring
and the runner are bladed. Figure 1.2 shows a cylindrical section through the guide ring
and the rotor, indicating the velocities in the absolute (  v) and the relative frame (  w).
Subscript 1 indicates the rotor inlet, subscript 2 the rotor outlet. The absolute frame is
attached to the stationary casing of the machine. The relative frame rotates together
with the rotor. The velocity u stands for the relative frame velocity (rotational speed Ω
1
2
guide ring
runner
draught tube
Fig. 1.1 Longitudinal section of an axial hydraulic turbine