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Wind Tunnels
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Intro

In the world of modern science, there is one element that keeps changing planes for the better. Wind tunnels aid in the testing and developing of safer, more fuel economizing, and faster planes. These wind tunnels are not something that have appeared out of thin air. The history of wind tunnels is a long one, but it is pretty simple. There are also many kinds of wind tunnels that mankind now use. This text, among other things, will also explain the different parts of the wind tunnels as well their functions. Wind tunnels are important, and they are also revolutionaries.


The Different Parts of a Wind Tunnel

The air flow in a wind Tunnel will start at the axial fan which helps with pressure regulations (Duncan, 2003; Nasa, 1999). The air flow will then follow a path going through the first diffuser (which helps with the steadiness of the airflow) (Duncan, 2003; Nasa, 1999), into the test section. In the test section, the plane, car, building, etc. is tested for the requirements of the specific test (the amount of air resistance for a plane, for example) (Duncan, 2003; Nasa, 1999). Next is the contraction, which reduces the speed of the air such that the ``regulating`` part of the speed tunnel is in a low speed zone (Duncan, 2003; Nasa, 1999). The settling chamber and the screens come next. These help regulate the turbulence, pressure and air uniformity (Duncan, 2003; Nasa, 1999). The honeycomb is another part of the wind tunnel that helps with the regulation of the flow (Duncan, 2003; Nasa, 1999). A wide angle diffuser is then added to prevent flow separation after the regulation (Duncan, 2003; Nasa, 1999). Corner vents are placed at all corners of a closed circuit wind tunnel, to help turn the wind 90*(Duncan, 2003; Nasa, 1999). Finally is the second diffuser, which aids in flow steadiness.

Supersonic Wind Tunnel

The Super Sonic wind tunnel is one that is not used often. The super sonic wind tunnel is capable of generating speeds of up to 5M (5 mach) (Flippone, 2004). A major problem of the super sonic wind tunnel is that it needs to generate super sonic speeds, and this is a real challenge to do (Flippone, 2004). The only way this can be achieved, is that a convergent-divergent nozzle needs to be used in the model, so it can achieve the right necessities (Flippone, 2004).

Low Speed Wind Tunnels


In a low speed wind tunnel, the air speed is significantly less than all other wind tunnels (Highbeam, 2007). The air speed of a low speed wind tunnel is slower than in any other wind tunnel, up to 400 Km/h, which is much smaller than the speed of sound propagation in air, which is 1240 Km/h (Flippone, 2004; Highbeam, 2007). This can also be said as 0.3 Mach Speed (Flippone, 2004). Low speed wind tunnels are open-return type (Flippone, 2004). In a low speed wind tunnel, the air is moved with a propulsion system made of a large axial fan that increases the dynamic pressure (Flippone, 2004). Low speed wind tunnels are used to test experimentally the aerodynamics of airplanes and cars before they are built (Flippone, 2004).

Transonic Wind Tunnels

Transonic Wind tunnels are wind tunnels that can achieve speeds close to the speed of sound (Flippone, 2004). In a transonic wind tunnel, there are many problems due to the reflection of shock waves (Flippone, 2004; Nasa, 1999). The highest speed, like in most wind tunnels, is reached in the test section (Flippone, 2004; Nasa, 1999). The speed of sound (the speed used in a transonic wind tunnel) corresponds to Mach numbers between 0.8 and 1.2 (Flippone, 2004).

Hotshot Wind Tunnels

Hotshots are wind tunnels that are used for the highest speeds (Mach 27) (Flippone, 2004). They are used to analyze the flow of air past ballistic missiles, space vehicles in atmospheric entry and certain objects in plasma physics (Flippone, 2004). Due to the high amount of speed and energy needed, they can only run for a second (or less) (Flippone, 2004). This ``extreme`` air speed is produced in an arc chamber with a near-vacuum in the other part of the tunnel. (Flippone, 2004).

Meteorological wind tunnels

These are tunnels used to study effects on suspension bridges, high-rise buildings, towers, dispersals of pollutants from factories (Flippone, 2004). These wind tunnels often have specific sizes (Flippone, 2004; Nasa, 1999). They are characterized by their long sizes (Flippone, 2004). In these wind tunnels, the most important thing is to stimulate the boundary layer (the immediate layer following the surface) (Flippone, 2004).

Wind Tunnels with moving ground


Wind tunnels with moving ground are used by the automobile industry, by racing cars teams, by the truck industry and for high-speed trains (Flippone, 2004). A moving belt is used for these special types of tunnels (Flippone, 2004). The ``moving belt`` is what makes these wind tunnels have moving ground. The moving belt is very important for cars that have very low ground clearance (Flippone, 2004).

Hypersonic wind tunnel


These are used to generate and test objects that fly around 5 times the speed of sound (Highbeam, 2007). It is used for speeds from 5 Mach to 15 Mach. (Flippone, 2004; TsAGi, 2006). There must be very high pressure ratios at the start (Flippone, 2004). High pressure and temperature ratios are need to be produced by a shock tube (Flippone, 2004). The moments that are measured are measured by changing certain parameters (angle of attack, or pressure) (TsAGi, 2006).


Early History of Wind Tunnels

The first (recorded) historical event considering wind tunnels happened in 1746. In 1746 Benjamin Robins (a British mathematician) proved that air resistance was a major factor in flight (US government, 2003; Wikipedia, 2007). Next, in 1804 Sir George Cayley created, built, and successfully flew a glider (US government, 2003; Wikipedia, 2007). In 1871 the first wind tunnel was made by Frank H. Wenham (US government, 2003). in 1889 Otto Lilienthal made some incorrect tests on planes, proving that wind tunnels are required for planes to run successfully (US government, 2003). Hiram Maxim built a wind tunnel in 1894 and the tests went so correctly, that when he flew the plane he could no predict how perfect it would fly, and the plane crashed (US government, 2003).
The Test Section

The test section is the part of the wind tunnel where the object is actually ``tested`` (Duncan, 2003). The test section is dependant on what is being tested (for instance a large one is needed for a large plane and a small one could be used for a small plane) (Duncan, 2003). The test section is also dependent on how that object is being tested (Duncan, 2003). Many Wind Tunnels have open (removable) test sections so they can test multiple objects (Duncan, 2003). The test section is normally where the highest speed is (Duncan, 2003; Flippone, 2004). The test section can come in all shapes and sizes, ranging from rectangular to oval (Duncan, 2003; Flippone, 2004).

Scientists Alan Garnett Davenport and Henry Coanda


Scientist Alan Garnett Davenport Pioneered the application of wind tunnels to the design of wind sensitive structures and worked to create international design standards for wind engineering (Science.ca Team, 2007) he also led studies for many important buildings, like the Normandy bridge and the World Trade Center (Science.ca Team, 2007). He has been leading studies for high efficiency low cost structures. (Science.ca Team, 2007). Henry Coanda was born in Bucharest on June 7, 1886 (ALLSTAR, 2004). Henry Coanda was a Romanian aerodynamical specialist (Wikipedia, 2007; ALLSTAR, 2004) and he also came up with his own aerodynamic effect; the Coanda Effect (Wikipedia, 2007; ALLSTAR, 2004). The Coanda effect is one of the effects that help planes fly, and is greatly studied in a wind tunnel (Wikipedia, 2007; ALLSTAR, 2004; A. Pope, J. J Harper, 1996). The Coanda effect is based on liquids getting attracted to certain objects (Wikipedia, 2007; ALLSTAR, 2004).

Conclusion


Wind tunnels have demonstrated themselves as crucial over the years. Wind tunnels have continued to increase the field of aeronautics, being a form of ``testing`` a plane, car, or other object, while making sure no disaster happens. Wind tunnels also continue to benefit the environment, making planes more fuel efficient. Most people do not think of wind tunnels as world changing, but wind tunnels demonstrate their hidden potential by producing better means of transportations.
Report on Wind Tunnels
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