A turbine extracts energy from a fluid that
possesses high head H;
2 types of turbines
High head is first converted
to high-velocity jets through
The jets hit turbine blades
as they pass by.
Usually bigger than reaction
Fluid fills the blade
passages, and pressure drop
occurs within the impeller.
Dynamic devices of either
radial-, mixed- or axial-flow
Low head, high flow devices
First efficient inward-flow turbine
was built by James B. Francis in
Radial- and mixed-flow design
are called Francis Turbines.
At lower head, a more compact
design will use an axial flow.
Kaplan type (adjustable blade)
High head, relatively low power.
Reaction turbines would require too
high a speed n and the high pressure
would require a thicker casing;
In the impulse turbine, the high
pressure is converted to high
velocity jets (atmospheric pressure)
through a nozzle. The jets hit a
bucket (elliptical split-cup shape)
The first efficient design was by
Lester A. Pelton (1880), so they are
called Pelton wheels.
The turbine parameters are similar to pumps, but defined as
a function of the output brake horsepower.
= = f ( C )
= = f ( C )
= ρgQH =
3 D 5
The maximum efficiency point is called the normal power.
n = 600 rpm, D = 2.25 ft, N sp = 29
A power specific speed can also be defined:
* 1/ 2
sp 5/ 4 1/ 2 5/ 4
ρ ( gH )
[ H ( ft)]
Turbine Type N sp range C H range
Impulse 1 – 10 15 - 50
Francis 10 -110 5 – 25
Prop: water 100 – 250 1 – 4
Prop: gas, steam 25 - 300 10 – 80
Rated Power: largest power
guaranteed by the
As opposed to normal power
which is delivered at
Four-blade Dutch-type windmill
American multiblade farm
wind energy to
The most popular design is
the 3-blade HAWT.
Efficient but awkward since
they require extensive
bracing and gears combined
with an electric generator.
VAWT: Vertical Axis Wind Turbine
Offers a simplified design, since the
gears are on the ground and the blades
strength requirements are lower.
But, less efficient and not self-starting.
Sold by Di Natura (Malta)
Darrieus (1925) wind turbine
Cap-Chat (Qc), biggest in the world
The maximum power available to the propeller of a wind
= mV &
The actual efficiency, and hence actual power produce, of a
wind turbine is expressed in terms of the power coefficient:
The maximum ideal limit for C P is given by the Betz number:
C P, max