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Wind tunnels are machines in which objects are held stationary inside a tube, and air is blown around it to study the interaction between the object and the moving air. They are used to test the aerodynamic effects of aircraft, rockets, cars, and buildings. Different wind tunnels range in size from less than a foot across, to over 100 feet (30 m), and can have air that moves at speeds from a light breeze to hypersonic velocities.
The Ames Research Center (ARC), also known as NASA Ames, is a major NASA research center at Moffett Federal Airfield in California's Silicon Valley. It was founded in 1939 as the second National Advisory Committee for Aeronautics (NACA) laboratory. That agency was dissolved and its assets and personnel transferred to the newly created National Aeronautics and Space Administration (NASA) on October 1, 1958. NASA Ames is named in honor of Joseph Sweetman Ames, a physicist and one of the founding members of NACA. At last estimate NASA Ames had over US$3 billion in capital equipment, 2,300 research personnel and a US$860 million annual budget.
Compressible flow is the branch of fluid mechanics that deals with flows having significant changes in fluid density. While all flows are compressible, flows are usually treated as being incompressible when the Mach number is smaller than 0.3. The study of compressible flow is relevant to high-speed aircraft, jet engines, rocket motors, high-speed entry into a planetary atmosphere, gas pipelines, commercial applications such as abrasive blasting, and many other fields.
Transonic flow is air flowing around an object at a speed that generates regions of both subsonic and supersonic airflow around that object. The exact range of speeds depends on the object's critical Mach number, but transonic flow is seen at flight speeds close to the speed of sound, typically between Mach 0.8 and 1.2.
The Arnold Engineering Development Complex (AEDC), Arnold Engineering Development Center before July 2012, is an Air Force Materiel Command facility under the control of the Air Force Test Center (AFTC). Named for General Henry "Hap" Arnold, the father of the U.S. Air Force, AEDC is the most advanced and largest complex of flight simulation test facilities in the world.
The University of Tennessee Space Institute (UTSI) is a satellite campus of the University of Tennessee located near Tullahoma, Tennessee.
Arnold Air Force Base is a United States Air Force base located in Coffee and Franklin counties, Tennessee, adjacent to the city of Tullahoma. It is named for General Henry "Hap" Arnold, the father of the U.S. Air Force.
Subsonic wind tunnels are used for operations at low Mach numbers, with speeds in the test section up to 480 km/h. They may be of open-return type or closed-return flow. These tunnels use large axial fans to move air and increase dynamic pressure, overcoming viscous losses. The design principles of subsonic wind tunnels are based on the continuity equation and Bernoulli's principle, which allow for the calculation of important parameters such as the tunnel's contraction ratio.
A Ludwieg tube is a cheap and efficient way of producing supersonic flow. Mach numbers up to 4 in air are easily obtained without any additional heating of the flow. With heating, Mach numbers of up to 11 can be reached.
A hypersonic wind tunnel is designed to generate a hypersonic flow field in the working section, thus simulating the typical flow features of this flow regime - including compression shocks and pronounced boundary layer effects, entropy layer and viscous interaction zones and most importantly high total temperatures of the flow. The speed of these tunnels vary from Mach 5 to 15. The power requirement of a wind tunnel increases linearly with its cross section and flow density, but cubically with the test velocity required. Hence installation of a continuous, closed circuit wind tunnel remains a costly affair. The first continuous Mach 7-10 wind tunnel with 1x1 m test section was planned at Kochel am See, Germany during WW II and finally put into operation as 'Tunnel A' in the late 1950s at AEDC Tullahoma, TN, USA for an installed power of 57 MW. In view of these high facility demands, also intermittently operated experimental facilities like blow-down wind tunnels are designed and installed to simulate the hypersonic flow. A hypersonic wind tunnel comprises in flow direction the main components: heater/cooler arrangements, dryer, convergent/divergent nozzle, test section, second throat and diffuser. A blow-down wind tunnel has a low vacuum reservoir at the back end, while a continuously operated, closed circuit wind tunnel has a high power compressor installation instead. Since the temperature drops with the expanding flow, the air inside the test section has the chance of becoming liquefied. For that reason, preheating is particularly critical.
A supersonic wind tunnel is a wind tunnel that produces supersonic speeds (1.2<M<5) The Mach number and flow are determined by the nozzle geometry. The Reynolds number is varied by changing the density level. Therefore, a high pressure ratio is required. Apart from that, condensation of moisture or even gas liquefaction can occur if the static temperature becomes cold enough. This means that a supersonic wind tunnel usually needs a drying or a pre-heating facility. A supersonic wind tunnel has a large power demand, so most are designed for intermittent instead of continuous operation.
The Unitary Plan Wind Tunnel, located at the NASA Ames Research Center in Moffett Federal Airfield, Mountain View, California, United States, is a research facility used extensively to design and test new generations of aircraft, both commercial and military, as well as NASA space vehicles, including the Space Shuttle. The facility was completed in 1955 and is one of five facilities created after the 1949 Unitary Plan Act supporting aeronautics research.
A Trisonic Wind Tunnel (TWT) is a wind tunnel so named because it is capable of testing in three speed regimes – subsonic, transonic, and supersonic. The earliest known trisonic wind tunnel was dated to 1950 and was located in El Segundo, California before it closed in 2007. Other trisonic wind tunnels currently in operation are those located at NASA's Marshall Space Flight Center, National Researach Council Canada's 1.5 m Trisonic Wind Tunnel Research Facility and the French-German Research Institute of Saint-Louis, ISRO's Vikram Sarabhai Space Centre(VSSC) in Thiruvananthapuram, India.
AEDC Aerodynamic and Propulsion Test Unit (APTU) is a blowdown hypersonic wind tunnel driven by a combustion air heater (CAH). The facility is owned by the United States Air Force and operated by Aerospace Testing Alliance.
AEDC Hypervelocity Wind Tunnel 9 is a hypersonic wind tunnel owned by the United States Air Force and operated by National Aerospace Solutions The facility can generate high Mach numbers and high Reynolds for hypersonic ground testing and the validation of computational simulations for the Air Force and Department of Defense.
The von Karman Gas Dynamics Facility at Arnold Engineering Development Complex, Arnold Air Force Base, Tennessee, provide aerothermal ground test simulations of hypersonic flight over a wide range of velocities and pressure altitudes. The facility consists of three Hypersonic wind tunnels: Tunnel A, B, and C. The wind tunnels can be run for several hours at a time thanks to a 92,500 horsepower air compressor plant system. The test unit is owned by the United States Air Force and operated by National Aerospace Solutions.
The Propulsion Wind Tunnel Facility, located at Arnold Engineering Development Complex, Arnold Air Force Base, Tennessee, holds three wind tunnels: the 16-foot transonic (16T), 16-foot supersonic (16S), and the aerodynamic 4-foot transonic (4T) tunnels. The facility is devoted to aerodynamic and propulsion integration testing of large-scale aircraft models. The tunnels are powered by a large compressor plant which allows the wind tunnels to run for extended periods of time. The test unit is owned by the United States Air Force and operated by Aerospace Testing Alliance.
AGARD-B is a standard wind tunnel model that is used to verify, by comparison of test results with previously published data, the measurement chain in a wind tunnel. Together with its derivative AGARD-C it belongs to a family of AGARD standard wind tunnel models. Its origin dates to the year 1952, and the Second Meeting of the AGARD Wind Tunnel and Model Testing Panel in Rome, Italy, when it was decided to define two standard wind tunnel model configurations to be used for exchange of test data and comparison of test results of same models tested in different wind tunnels. The idea was to establish standards of comparison between wind tunnels and improve the validity of wind tunnel tests. Among the standard wind tunnel models, AGARD model configuration B (AGARD-B) has become by far the most popular. Initially intended for the supersonic wind tunnels, the AGARD-B configuration has since been tested in many wind tunnels at a wide range of Mach numbers, from low subsonic, through transonic to hypersonic. Therefore, a considerable database of test results is available.
The Aircraft Research Association (ARA) is an aerodynamics research institute in the north-west of Bedford.
References
- ↑ "Supersonic Wind Tunnel" . Retrieved 2007-08-13.
- ↑ "Arc-Heater" . Retrieved 2007-08-13.