Editing Wind tunnel (section)

==History==

===Origins===

English mathematician and physicist [[Isaac Newton]] (1642–1726) displayed a forerunner to the modern wind tunnel in Proposition 36/37 of his book ''[[Philosophiæ Naturalis Principia Mathematica]]''.<ref>{{Cite book |url=https://books.google.com/books?id=Ppv5h4sgAYwC&pg=PA269 |title=Isaac Newton's Natural Philosophy |date=2001 |publisher=MIT Press |isbn=978-0-262-52425-4 |editor-last=Buchwald |editor-first=Jed Z. |series= |location=Cambridge, Mass. |pages=269 |editor-last2=Newton |editor-first2=Isaac}}</ref><ref>{{Cite book |last=Rowlands |first=Peter |url=https://books.google.com/books?id=u0NBDwAAQBAJ&pg=PA152 |title=Newton – Innovation And Controversy |publisher=[[World Scientific Publishing]] |year=2017 |isbn=9781786344045 |pages=152–153}}</ref>

English military engineer and mathematician [[Benjamin Robins]] (1707&ndash;1751) invented a [[whirling arm]] apparatus to determine drag<ref>{{cite book |editor=Wilson, James |title=Mathematical Tracts of the late Benjamin Robins, Esq |location=London |publisher=J. Nourse |date=1761 |volume=1 |chapter=An account of the experiments, relating to the resistance of the air, exhibited at different times before the Royal Society, in the year 1746 |chapter-url=https://books.google.com/books?id=ha82AAAAMAAJ&pg=PA202}}</ref> and did some of the first experiments in aerodynamics.

[[Sir George Cayley]] (1773–1857) also used a whirling arm to measure the drag and lift of various airfoils.<ref>{{Cite journal|author=J. A. D. Ackroyd|year=2011|title=Sir George Cayley: The Invention of the Aeroplane near Scarborough at the Time of Trafalgar|journal=Journal of Aeronautical History|volume=1|pages=130–81 |url=http://aerosociety.com/Assets/Docs/Publications/The%20Journal%20of%20Aeronautical%20History/2011-06Cayley-Ackroyd2.pdf |archive-url=https://web.archive.org/web/20131226050808/http://aerosociety.com/Assets/Docs/Publications/The%20Journal%20of%20Aeronautical%20History/2011-06Cayley-Ackroyd2.pdf |archive-date=2013-12-26 |url-status=live}}</ref> His whirling arm was {{convert|5|ft|m}} long and attained speeds between 10 and 20 feet per second (3 to 6&nbsp;m/s).

[[Otto Lilienthal]] used a rotating arm to make measurements on wing airfoils with varying [[angle of attack|angles of attack]], establishing their [[lift-to-drag ratio]] polar diagrams, but was lacking the notions of [[induced drag]] and [[Reynolds numbers]].<ref>{{cite news |url= https://leehamnews.com/2017/10/27/bjorns-corner-aircraft-drag-reduction-part-2/ |title= Bjorn's Corner: Aircraft drag reduction, Part 2 |author= Bjorn Fehrm |date= 27 October 2017 |work= Leeham}}</ref>

[[File:Wright Brothers Wind Tunnel Replica.jpg|thumb|Replica of the Wright brothers' wind tunnel]]

Drawbacks of whirling arm tests are that they do not produce a reliable flow of air. Centrifugal forces and the fact that the object is moving in its own wake also mean that detailed examination of the airflow is difficult. [[Francis Herbert Wenham]] (1824–1908), a Council Member of the [[Aeronautical Society of Great Britain]], addressed these issues by inventing, designing, and operating the first enclosed wind tunnel in 1871.<ref>{{cite book |title=A Dictionary of Aviation |first=David W. |last=Wragg |isbn=9780850451634 |edition=first |publisher=Osprey |year=1973 |page=281}}</ref><ref>Note:
* That Wenham and Browning were attempting to build a wind tunnel is briefly mentioned in:  ''Sixth Annual Report of the Aeronautical Society of Great Britain for the Year 1871'', p. 6. [https://babel.hathitrust.org/cgi/pt?id=uc1.b4513625;view=1up;seq=444 From p. 6:]  "For this purpose [viz, accumulating experimental knowledge about the effects of wind pressure], the Society itself, through Mr. Wenham, had directed a machine to be constructed by Mr. Browning, who, he was sure, would take great interest in the work, and would give to it all the time and attention required."
* In 1872, the wind tunnel was demonstrated to the Aeronautical Society.  See:  ''Seventh Annual Report of the Aeronautical Society of Great Britain for the Year 1872'', [https://babel.hathitrust.org/cgi/pt?id=uc1.b4513626;view=1up;seq=10 pp. 6–12.]</ref> Once this breakthrough had been achieved, detailed technical data was rapidly extracted by the use of this tool. Wenham and his colleague John Browning are credited with many fundamental discoveries, including the measurement of l/d ratios, and the revelation of the beneficial effects of a high [[Aspect ratio (wing)|aspect ratio]].

[[Konstantin Tsiolkovsky]] built an open-section wind tunnel with a centrifugal blower in 1897, and determined the [[drag coefficient]]s of flat plates, cylinders, and spheres.

Danish inventor [[Poul la Cour]] used wind tunnels to develop [[wind turbine]]s in the early 1890s.
[[Carl Rickard Nyberg]] used a wind tunnel to design his ''[[Flugan]]'' starting in 1897.

The Englishman [[Osborne Reynolds]] (1842–1912) of the [[University of Manchester]] demonstrated that the airflow pattern over a scale model would be the same for the full-scale vehicle if a certain flow parameter were the same in both cases. This parameter, now known as the [[Reynolds number]], is used in the description of all fluid-flow situations, including the shape of flow patterns, the effectiveness of heat transfers, and the onset of turbulence. This comprises the central scientific justification for the use of models in wind tunnels to simulate real-life phenomena.

The [[Wright brothers]]' use of a simple wind tunnel in 1901 to study the effects of airflow over various shapes while developing their [[Wright Flyer]] was in some ways revolutionary.<ref name=Dodson>{{cite journal |author1=Dodson, MG |title=An Historical and Applied Aerodynamic Study of the Wright Brothers' Wind Tunnel Test Program and Application to Successful Manned Flight |website=Defence Technical Information Center |date=2005 |url=https://apps.dtic.mil/sti/citations/ADA437187}}</ref> However, they were using the accepted technology of the day, though this was not yet a common technology in America.

In [[France]], [[Gustave Eiffel]] (1832–1923) built his first open-return wind tunnel in 1909, powered by a {{cvt|50|kW|hp|order=flip}} electric motor, at Champs-de-Mars, near the foot of the tower that bears his name.

Between 1909 and 1912 Eiffel ran about 4,000 tests in his wind tunnel, and his systematic experimentation set new standards for aeronautical research.
In 1912 [[Laboratoire Aerodynamique Eiffel|Eiffel's laboratory]] was moved to Auteuil, a suburb of Paris, where his wind tunnel with a {{convert|2|m|ft|order=flip|adj=on|sigfig=1}} test section is still operational today.<ref>{{cite web | url=https://www.aerodynamiqueeiffel.fr/ |title = Laboratoire Aerodynamique Eiffel}}</ref> Eiffel significantly improved the efficiency of the open-return wind tunnel by enclosing the test section in a chamber, designing a flared inlet with a honeycomb flow straightener, and adding a diffuser between the test section and the fan located at the downstream end of the diffuser; this was an arrangement followed by a number of wind tunnels later built; in fact the open-return low-speed wind tunnel is often called the Eiffel-type wind tunnel.

=== Widespread usage ===
[[File:Messerschmitt Bf 109E wind tunnel testing at the Deutsche LFA.jpg|right|thumb|250px|Herman Goering tunnel A3 commissioned in 1940<ref name="AeroRsh">{{cite book | url=https://link.springer.com/book/10.1007/978-3-642-18484-0 |title=Aeronautical Research in Germany|author1=Hirschel, Ernst Heinrich |author2=Prem, Horst |author3=Madelung, Gero |page=194|ref=refAeroRsh2004}}</ref> showing open test section with [[Messerschmitt Bf 109]]F installed for testing.]]

Subsequent use of wind tunnels proliferated as the science of aerodynamics and discipline of aeronautical engineering were established and air travel and power were developed.

The US Navy in 1916 built one of the largest wind tunnels in the world at that time at the Washington Navy Yard. The inlet was almost {{convert|11|ft|m}} in diameter and the discharge part was {{convert|7|ft|m}} in diameter. A {{cvt|500|hp|kW}} electric motor drove the paddle type fan blades.<ref>{{Citation|url=https://books.google.com/books?id=V3fmAAAAMAAJ&pg=PA426|title=US Navy Experimental Wind Tunnel|year=1915 }}</ref>

In 1931 the NACA built a {{convert|30|by|60|ft|m|adj=on}} [[Full-Scale Wind Tunnel|full-scale wind tunnel]] at Langley Research Center in Hampton, Virginia. The tunnel was powered by a pair of fans driven by {{cvt|4000|hp|kW}} electric motors. The layout was a double-return, closed-loop format and could accommodate many full-size real aircraft as well as scale models. The tunnel was eventually closed and, even though it was declared a [[National Historic Landmark]] in 1995, demolition began in 2010.

Until World War II, the world's largest wind tunnel, built in 1932–1934, was located in a suburb of Paris, [[Chalais-Meudon]], France.{{Citation needed|date=December 2021|reason=The Popular Mechanics article in the next citation does not mention the name of the suburb nor that the wind tunnel is the largest.}}  It was designed to test full-size aircraft and had six large fans driven by high powered electric motors.<ref>{{Cite magazine |title=Man-Made Hurricane Tests Full-Sized Planes; Giant Battery of Fans Helps Makes Flying Safe |url=https://books.google.com/books?id=QdsDAAAAMBAJ&pg=PA94 |magazine=[[Popular Mechanics]] |date=19 January 1936 |pages=94–95|via=Google Books}}</ref> The Chalais-Meudon wind tunnel was used by [[ONERA]] under the name S1Ch until 1976 in the development of, e.g., the [[Sud Aviation Caravelle|Caravelle]] and [[Concorde]] airplanes. Today, this wind tunnel is preserved as a national monument.

[[Ludwig Prandtl]] was [[Theodore von Kármán]]'s teacher at [[Göttingen University]] and suggested the construction of a wind tunnel for tests of airships they were designing.<ref name=TvK>[[Theodore von Kármán]] (1967) ''The Wind and Beyond''</ref>{{rp|44}} The [[vortex street]] of turbulence downstream of a cylinder was tested in the tunnel.<ref name=TvK/>{{rp|63}} When he later moved to [[Aachen University]] he recalled use of this facility:

<blockquote>I remembered the wind tunnel in Göttingen was started as a tool for studies of Zeppelin behavior, but that it had proven to be valuable for everything else from determining the direction of smoke from a ship's stack, to whether a given airplane would fly. Progress at Aachen, I felt, would be virtually impossible without a good wind tunnel.<ref name=TvK/>{{rp|76}}</blockquote>

When von Kármán began to consult with [[Caltech]] he worked with [[Clark Millikan]] and Arthur L. Klein.<ref name=TvK/>{{rp|124}} He objected to their design and insisted on a return flow making the device "independent of the fluctuations of the outside atmosphere". It was completed in 1930 and used for [[Northrop Alpha]] testing.<ref name=TvK/>{{rp|169}}

In 1939 [[General Arnold]] asked what was required to advance the USAF, and von Kármán answered, "The first step is to build the right wind tunnel."<ref name=TvK/>{{rp|226}} On the other hand, after the successes of the [[Bell X-2]] and prospect of more advanced research, he wrote, "I was in favor of constructing such a plane because I have never believed that you can get all the answers out of a wind tunnel."<ref name=TvK/>{{rp|302–03}}

===World War II===
In 1941 the US constructed one of the largest wind tunnels at that time at Wright Field in Dayton, Ohio. This wind tunnel starts at {{convert|45|ft|m}} and narrows to {{convert|20|ft|m}} in diameter. Two {{convert|40|ft|m|adj=on}} fans were driven by a {{cvt|40000|hp|kW}} electric motor. Large scale aircraft models could be tested at air speeds of {{convert|400|mph|km/h|abbr=on}}.<ref>{{Citation|url=https://books.google.com/books?id=mtkDAAAAMBAJ&pg=PA14|title=400mph Wind Tests Planes|date=July 1941 |publisher=Hearst Magazines }}</ref>

During WWII, Germany developed different designs of large wind tunnels to further their knowledge of aeronautics. For example, the wind tunnel at [[Peenemünde]] was a novel wind tunnel design that allowed for high-speed airflow research, but brought several design challenges regarding constructing a high-speed wind tunnel at scale. However, it successfully used some large natural caves which were increased in size by excavation and then sealed to store large volumes of air which could then be routed through the wind tunnels. By the end of the war, Germany had at least three different supersonic wind tunnels, with one capable of Mach 4.4 heated airflows.

A large wind tunnel under construction near [[Oetztal]], Austria would have had two fans directly driven by two {{cvt|50,000|hp|kW}} [[hydropower|hydraulic turbines]]. The installation was not completed by the end of the war and the dismantled equipment was shipped to [[Modane]], France in 1946 where it was re-erected and is still operated there by the [[ONERA]]. With its {{convert|8|m|ft|order=flip|adj=on}} test section and airspeed up to Mach 1, it is the largest transonic wind tunnel facility in the world.<ref name=EH04>[[#refAeroRsh2004|Aeronautical Research (2004)]], p.87.</ref> [[Frank Wattendorf]] reported on this wind tunnel for a US response.<ref>{{cite journal | author1=Wattendorf, F.L.| date=May 1946| title=Reports on selected topics of German and Swiss aeronautical developments|url=https://www.governmentattic.org/TwardNewHorizons.html|journal=Toward New Horizons|format=Governmentattic}}</ref>

On 22 June 1942, Curtiss-Wright financed construction of one of the nation's largest subsonic wind tunnels in Buffalo, New York. The first concrete for building was poured on 22 June 1942 on a site that eventually would become [[Calspan]], where the wind tunnel still operates.<ref>{{cite web|url=https://calspan.com/company/history |title=Calspan History > Wind Tunnel Construction |publisher=calspan.com |access-date=2015-04-23}}</ref>

By the end of World War II, the US had built eight new wind tunnels, including the largest one in the world at Moffett Field near [[Sunnyvale, California]], which was designed to test full size aircraft at speeds of less than {{cvt|250|mph|kph}}<ref>{{Citation|chapter-url=https://books.google.com/books?id=TCEDAAAAMBAJ&pg=PA66|chapter=Wind at Work For Tomorrow's Planes|title=Popular Science|date=July 1946|pages=66–72|publisher= Hearst Magazines}}</ref> and a vertical wind tunnel at Wright Field, Ohio, where the wind stream is upwards for the testing of models in spin situations and the concepts and engineering designs for the first primitive helicopters flown in the US.<ref>{{Citation|chapter-url=https://books.google.com/books?id=AyEDAAAAMBAJ&pg=PA73|chapter= Vertical Wind Tunnel|date= February 1945|title=Popular Science|publisher= Hearst Magazines}}</ref>

===After World War II===
[[File:National Advisory Committee for Aeronautics wind tests (1946).webm|thumb|[[National Advisory Committee for Aeronautics|NACA]] wind tunnel test on a human subject, showing the effects of high wind speeds on the human face]]
Later research into airflows near or above the speed of sound used a related approach. Metal pressure chambers were used to store high-pressure air which was then accelerated through a [[de Laval nozzle|nozzle]] designed to provide supersonic flow. The observation or instrumentation chamber ("test section") was then placed at the proper location in the throat or nozzle for the desired airspeed.
[[File:Mary Jackson in a wind tunnel with a model at NASA Langley.jpg|thumb|left|[[Mary Jackson (engineer)|Mary Jackson]] with a wind tunnel model at [[Langley Research Center]]]]
In the United States, concern over the lagging of American research facilities compared to those built by the Germans led to the [[Unitary Wind Tunnel Plan Act]] of 1949, which authorized expenditure to construct new wind tunnels at universities and at government sites. Some German war-time wind tunnels were dismantled for shipment to the United States as part of the plan to exploit German technology developments.<ref name=Hiebert02>{{cite web|url=http://www.arnold.af.mil/shared/media/document/AFD-120305-099.pdf|first=David M.|last=Hiebert|title=Public Law 81-415: The Unitary Wind Tunnel Plan Act of 1949 and the Air Engineering Development Center Act of 19491|year=2002|access-date=2014-04-03|archive-date=9 March 2013|archive-url=https://web.archive.org/web/20130309140831/http://www.arnold.af.mil/shared/media/document/AFD-120305-099.pdf}}</ref>

[[File:16 Foot Transonic Tunnel Rehabilitation - GPN-2000-001300.jpg|thumb|right|250px|Fan blades of [[Langley Research Center]]'s 16-foot [[transonic]] wind tunnel in 1990, before it was retired in 2004]]

In the United States, many wind tunnels have been decommissioned from 1990 to 2010, including some historic facilities. Pressure is brought to bear on remaining wind tunnels due to declining or erratic usage, high electricity costs, and in some cases the high value of the real estate upon which the facility sits. On the other hand, CFD validation still requires wind-tunnel data, and this is likely to be the case for the foreseeable future. Studies have been done and others are underway to assess future military and commercial wind tunnel needs, but the outcome remains uncertain.<ref>Goldstein, E., "Wind Tunnels, Don't Count Them Out," ''Aerospace America'', Vol. 48 #4, April 2010, pp. 38–43</ref> More recently an increasing use of jet-powered, instrumented unmanned vehicles, or research drones, have replaced some of the traditional uses of wind tunnels.<ref>Benjamin Gal-Or, ''Vectored Propulsion, Supermaneuverability & Robot Aircraft'', Springer Verlag, 1990, {{ISBN|0-387-97161-0|3-540-97161-0}}</ref> The world's fastest wind tunnel as of 2019 is the LENS-X wind tunnel, located in Buffalo, New York.<ref>{{cite web|url=https://www.scmp.com/news/china/policies-politics/article/2120072/china-builds-worlds-fastest-wind-tunnel-test-weapons|title=China gears up to test weapons that could hit US in 14 minutes|date=15 November 2017|website=South China Morning Post}}</ref>