28
2 Wind Tunnels and Other Aerodynamic Test Facilities
air to avoid creating a parasitic boundary layer. To reproduce the ground effect, the
vehicle tested (or its model) must be mounted above a rolling belt travelling at the
simulated vehicle velocity (see Sect. 3.3).
The wind tunnels very practical experimental facilities which have quickly
imposed themselves at the expense of alternative means based on the direct
displacement of the object in the air either by:
– Horizontal: the case of the airplane tests carried out by the German company
Siemens in 1901 on a train launched at 160 km/h, a technique also used by the
Institut Aérotechnique (IAT) of Saint-Cyr-l’École in 1909 on a private railroad
track of 1.4 km, also the wing profiles tests by Armand de Gramont (the Duc de
Guiche) on his motor vehicle.
– Vertical: the guided free fall made in 1908 by Gustave Eiffel from the second floor
of the eponymous tower.
– Combination of both, while taking advantage of gravity effect to move an object
along a cable: method experienced in 1904 by Ferdinand Ferber in the valley of
Meudon to launch his plane hanging on a cart sliding along a cable stretched over
pylons. Gustave Eiffel also considered such a device (which he called aerodrome)
from the first floor of his tower, before the realisation of his wind tunnel.
Rotational movement: the tested object is fixed at the end of a long rotating arm,
this means making it possible to reach significantly higher tangential speeds by
extending the rotating arm and the speed of rotation. Such a device was set up in
1906 at the IAT.
Except for a few applications of limited scope, the previous means were quickly
abandoned because of their obvious disadvantages.
In general, a wind tunnel consists of a test section placed in a circuit where a
stream of air is maintained by a fan or a compressor. In some wind tunnels, called
blow down wind tunnel, the flow results from the discharge of compressed air stored
in a tank. There are two types of wind tunnels.
2.1.2 The Eiffel Type or Open Circuit Wind Tunnel
In this arrangement, the air collected upstream is accelerated in a contraction consisting of a conduit of convergent section; then the air flows through the test section
before being directly discharged into the atmosphere. The fluid motion is ensured by
the suction effect of a fan placed near the outlet of the wind tunnel. A major innovation from Gustave Eiffel consisted of inserting between the test section and the fan
located downstream, a divergent part called diffuser (Eiffel patent dated November
28, 1911). This device reduces drastically the power required for the operation of
the installation. Its effectiveness stems from Bernoulli’s law which states that pressure and velocity are inversely proportional. Therefore, the diffuser, by reducing the
velocity, has the effect of compressing the air. Then the static pressure difference on
either side of the fan can be much lower to compensate for when the fan is placed
2 Wind Tunnels and Other Aerodynamic Test Facilities
air to avoid creating a parasitic boundary layer. To reproduce the ground effect, the
vehicle tested (or its model) must be mounted above a rolling belt travelling at the
simulated vehicle velocity (see Sect. 3.3).
The wind tunnels very practical experimental facilities which have quickly
imposed themselves at the expense of alternative means based on the direct
displacement of the object in the air either by:
– Horizontal: the case of the airplane tests carried out by the German company
Siemens in 1901 on a train launched at 160 km/h, a technique also used by the
Institut Aérotechnique (IAT) of Saint-Cyr-l’École in 1909 on a private railroad
track of 1.4 km, also the wing profiles tests by Armand de Gramont (the Duc de
Guiche) on his motor vehicle.
– Vertical: the guided free fall made in 1908 by Gustave Eiffel from the second floor
of the eponymous tower.
– Combination of both, while taking advantage of gravity effect to move an object
along a cable: method experienced in 1904 by Ferdinand Ferber in the valley of
Meudon to launch his plane hanging on a cart sliding along a cable stretched over
pylons. Gustave Eiffel also considered such a device (which he called aerodrome)
from the first floor of his tower, before the realisation of his wind tunnel.
Rotational movement: the tested object is fixed at the end of a long rotating arm,
this means making it possible to reach significantly higher tangential speeds by
extending the rotating arm and the speed of rotation. Such a device was set up in
1906 at the IAT.
Except for a few applications of limited scope, the previous means were quickly
abandoned because of their obvious disadvantages.
In general, a wind tunnel consists of a test section placed in a circuit where a
stream of air is maintained by a fan or a compressor. In some wind tunnels, called
blow down wind tunnel, the flow results from the discharge of compressed air stored
in a tank. There are two types of wind tunnels.
2.1.2 The Eiffel Type or Open Circuit Wind Tunnel
In this arrangement, the air collected upstream is accelerated in a contraction consisting of a conduit of convergent section; then the air flows through the test section
before being directly discharged into the atmosphere. The fluid motion is ensured by
the suction effect of a fan placed near the outlet of the wind tunnel. A major innovation from Gustave Eiffel consisted of inserting between the test section and the fan
located downstream, a divergent part called diffuser (Eiffel patent dated November
28, 1911). This device reduces drastically the power required for the operation of
the installation. Its effectiveness stems from Bernoulli’s law which states that pressure and velocity are inversely proportional. Therefore, the diffuser, by reducing the
velocity, has the effect of compressing the air. Then the static pressure difference on
either side of the fan can be much lower to compensate for when the fan is placed