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the best-developed structural and aerodynamic windmill technology with newly developing
electrical technology. At the same time that it was doing this, it demonstrated that the
production of electrical power was unlikely to be a future application of low-speed, multi-
blade rotors. It could be said that this was a very successful operation, but the patient died.
The next important step in the transition from windmills to wind turbine generators was
taken by professor Poul LaCour in Denmark [Juul 1956], again at the turn of the century.
LaCour was a scientist who conducted wind turbine research from 1891, the year of his
appointment to an experimental station at Askov, until his death in 1907. He put the
principles of the new engineering science of aerodynamics into use in the
LaCour windmill,
and he was one of the irst in the world to use a wind tunnel. Figure l-19(a) shows
LaCour's wind tunnel, with a model rotor in position for testing in the free stream just for-
ward of the outlet of the tunnel. The four-bladed rotor at the tunnel inlet is the fan that drove
the air low.
As we see in Figure 1-19(b), LaCour's rotors still followed the four-bladed, twisted,
rectangular pattern of the conventional European windmill, but he appreciated the
advantages of low
solidity
(ratio of sail area to
swept area
),
leading-edge camber, and low
drag. After several years of experimentation, LaCour laid down a set of rules for obtaining
optimum rotor performance and succeeded in developing practical wind machines for
producing electricity. He designed wind power plants generating 5 to 25 kW for
agricultural and village use, and by 1910 several hundred of these were operating in
Denmark. Then along came the diesel, and the beginning of the oscillating fortunes of the
windmill, whether for generating electricity or pumping water.
In summary, the transition from windmills supplying mechanical power to wind
turbines producing electrical energy took place during the last dozen years of the nineteenth
century. Brush's high-solidity post-mill design and LaCour's more practical, low-solidity
tower-mill conigurations pioneered the stand-alone units that generate DC electricity
for charging storage batteries. As we see in the next section, this was practically the only
application of wind-generated electricity until the beginning of World War II.
Figure 1-19. LaCour's adaptation of a windmill for generating DC electricity at Askov
in Denmark around the turn of the century.
(a) LaCour's wind tunnel, c. 1895, one of the
irst in the world. (Juul 1956) (b) A four-bladed LaCour windmill.
(©1955, E.W. Golding;
1976, E.&F.N. Spon Ltd.; reprinted by Halsted Press, John Wiley & Sons, Inc.)
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