1247 Hypersonic Facilities Complex
|Facility 1247 Complex|
|Center:||Langley Research Center|
|Historic Eligibility:||National Register Eligible|
|Important Tests:||Gemini, Apollo, Viking, Space Shuttle|
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This facility housed the most active hypersonic research group in the nation. The large vacuum spheres beside the building are evacuated to give low starting pressure for eight hypersonic wind tunnels that cover a range from six to twenty times the speed of sound. Major NASA projects that have been supported here include the X-15 experimental aircraft; Mercury, Gemini, Apollo and Viking spacecraft; and the Space Shuttle. Work has supported future shuttles, hypersonic commercial transports, and military systems.
The Hypersonic Facilities Complex, originally named the Gas Dynamics Laboratory, was the NACA’s earliest installation with multiple hypersonic wind tunnels. The various tunnels utilized air and, later, specific gasses, particularly helium and nitrogen, to investigate aerodynamic and aerothermodynamic problems in flight regimes above the speed range of Mach 5. The facility’s core tunnels have been blowdown-type tunnels powered by common differential-pressure systems.
The Hypersonic Facilities Complex (HFC) was part of the large investment Congress made in NACA facilities during the late 1940s and early 1950s to support high-speed-flight research. Wind tunnels for the supersonic and transonic flight regimes were conventional, closed-circuit tunnels. Large, powerful, and expensive, the new tunnels, particularly the Unitary Plan Wind Tunnels, for speeds up to about Mach 4.5 generally resembled their subsonic predecessors, even though their test sections incorporated key new features and their drive power increased dramatically. Wind tunnels for speeds in the hypersonic range (Mach 5 and higher) presented conditions too extreme to achieve with this design. As in supersonic tunnels, converging-diverging nozzles can be designed to produce hypersonic speeds, but the high pressure and temperature differentials involved mean that the chemical and physical properties of the test gas must be considered. Hypersonic nozzles typically have exit-to- throat ratios on the order of 20 – 30 to 1. Most gasses, including air, will liquefy leaving the throat of such nozzles, thanks to a drastic drop in temperature. To prevent liquefaction, the gas must be heated to 1,000 F, or more, before it enters the nozzle. This means that most nozzles need to be cooled to prevent distortion and degradation. Similarly, high pressures, often above 1,000 pounds per square inch, are necessary to achieve the proper mass flow through the nozzle. Such extremes dictated a facility unlike any other at Langley.
John Stack, the indomitable head of Langley’s Compressibility Research Division, championed the idea of a facility that had a common gas system with a large pressurized sphere serving several blowdown tunnels. Each tunnel would be designed to different specifications so that they complimented one another, giving the facility a wide range of testing capabilities. Antonio Ferri, an Italian researcher who had joined his staff after World War II, had experience with high-speed blowdown facilities in Europe, agreed in principle, but Ferri and engineer Macon C. Ellis, took the idea a step further. They replaced the single, large pressure sphere with a rack of small-diameter bottles capable of holding air at a much-higher pressure, as much as 5,000 pounds per square inch (borrowing a technique that had worked well aboard submarines). They then converted Stack’s big sphere into a vacuum vessel. Connecting tunnels between the two would yield the highest possible differential pressure across the tunnels’ nozzles.
This multi-tunnel concept for the Gas Dynamics Laboratory received approval from Congress in 1949. At $5.5 million, its initial cost was more than twice that of any other facility at Langley, though the price tag for Langley’s Unitary Plan Tunnel, approved later the same year, would triple that staggering figure. During these early years of the Cold War—the Soviet Union detonated its first atomic bomb in 1949—Congress was in the mood to maximize America’s investment in aeronautical research and, thus, ensure its strength in high-speed aviation and the emerging field of guided missiles.
Many of the problems tackled by HFC researchers in its early years involved conditions that would be experienced by guided missiles, especially by nuclear warheads re-entering the atmosphere on the downward side of their ballistic trajectories. At Mach 5 – 10, the problems involved not only aerodynamic stability, but also searing heat generated by both air friction in the boundary layer and the high compression in shock waves. Finding designs that minimized the heat exposure while maintaining a predictable flight path and materials that could withstand 2,000-plus Fahrenheit temperatures quickly became inter-related problems that NACA researchers tackled at both Ames and Langley.
Research operations and equipment assignments in the Hypersonic Facilities Complex have changed many times since its opening, and its tunnels have been removed, installed, modified, and relocated in a bewildering manner, but it is the intelligent initial design of such a flexible facility that has made these alterations to meet changing needs possible. Compared to the cost of new construction that might otherwise be needed to accommodate new tunnels, the savings to NASA, though difficult to estimate, have been, and continue to be, enormous.
[top] Facilities in Complex
1247A - 1952 - originally known as the Gas Dynamics Laboratory Center, by 1965 was known as the Hypersonic Blowdown Tunnels; 31-Inch Mach 10 Tunnel
1247B - 1952 - originally known as the Gas Dynamics Laboratory West Wing, by 1965 was referred to as the Hypersonic Blowdown Tunnels Space Environment Research; Hypersonic Helium Tunnel and Hypersonic Nitrogen Tunnel; 1981 referred to as the High Reynolds Number Helium Tunnels, the M10 leg of the facility was removed; in 1995, the following tunnels were operational: 22-Inch M20 Helium Tunnel (Rm 102), the Open Jet Leg Helium Tunnel (Rm 105), the 2-X6-Inch Low Speed Tunnel (Rm 108), the 20-Inch M17 Nitrogen Tunnel (Rm 109), the M6 Arc-Heated Scramjet (Rm 111 - scramjet motor moved from building 1235) and the 15-Inch Low Turbulence Tunnel (Rm 115); by 2005, three tunnels were closed: 2X6-Inch LST, the M17 Nitrogen, and the Open Jet Leg
1247C - 1952 - Cooling Tower
1247D - 1952 - 20-Inch Mach 6 Tunnel and Mach 8 Variable Density Tunnel
1247E - 1952 - High-Pressure Air or Compressor Station
1247F - 1952 - Ames Substation
1247H - 1967 - originally the 60-Inch Mach 18 Helium Tunnel and the Mach 20 Helium Tunnel, in 1977 the Mach 40 Helium Tunnel
1247J - 1991 - Vacuum Pump Station
[top] Tunnels in the Hypersonic Complex
[top] 22-Inch Helium Tunnel
This conventional tunnel in room B102, opened in 1960, was originally named the Hypersonic Helium Tunnel. Three axisymmetric nozzles for it were built to deliver Mach 18, 22, and 26 flows, but only the Mach 22 nozzle has been calibrated, and it has been the one most-frequently utilized. The test section measures 221/2 inches in diameter, which provides a core test region between 8 and 10 inches in diameter. Helium is supplied from high-pressure bottles and exhausted into one, or more, vacuum spheres. A hydraulically-actuated mechanism inserts a model into the stabilized flow, and a second, similar device does the same for a shield that protects the model from start-up transients or debris. The flow is established by opening quick-acting valves and stabilized with a quick-response nozzle-throat plug. Helium is recovered from the vacuum sphere after a test for re-use. This tunnel’s primary modification involved the addition of a second circuit featuring a larger test chamber known as the Open-Jet Leg. The original circuit, then referred to as the Aerodynamic Leg, remained in service until being closed about 2003. It was demolished about 2007.
Programs supported during the 1990s included:
- Aerospace Plane 1986-1993
- Space Shuttle 1970-1997
- Advanced Manned Launch System (AMLS) 1991-1998
- Assured Crew Return Vehicle (ACRV) 1990-1995
- Hypersonic Flight Text Experiment (Hyflite) 1993-1998
- Personnel Launch System (PLS) 1988-1996
- Space Exploration Aerobraking 1986-1996
1963 Diagram of the Aerodynamics Leg of 22-Inch Helium Tunnel
[top] Hypersonic Helium Tunnel Open-Jet Leg
The Open-Jet Leg in room B105 was an addition to the 22-Inch Helium Tunnel that opened in 1969. It utilized two axisymmetric nozzles, on that produced Mach 20 flow at its 22-inch exit and a second that generated Mach 40 flow at its 36-inch exit. Either discharged into a larger test section, where a model-injection device swung the model into the flow centerline after steady flow had been established. The support mechanism allowed the angle of attack to vary ±20 degrees. As with the Aerodynamic Leg, heat was not required to prevent liquefaction during Mach 20 tests, but heat from the building’s heaters was needed for those at Mach 40. Run time was approximately 20 seconds. With a declining interest in hypersonic research and budgetary constraints during the 1990s, NASA decided to close this tunnel and subsequently demolish it about 1998.
[top] 60-Inch Mach 18 Helium Tunnel
One of the facility’s original tunnels, this conventional tunnel, also known as the Mach 20 High-Reynolds Number Helium Tunnel and as one of the Hypersonic Aeroelasticity Tunnels, opened in 1952 in room B107 as the NACA’s largest helium tunnel. It featured axisymmetric nozzles for Mach 16.5 and Mach 18 using gas supplied by the building’s 5,000 pound-per-square-inch helium system and recovered from the 60-foot-diameter vacuum spheres on the building’s southwest side. Most runs involved the use of two spheres and lasted 5 – 10 seconds. Models were sting- or strut-mounted with a variable angle-of-attack adjustment. An electron-bombardment system for flow visualization was available, as was a spark schlieren photography system. Ambient temperatures were adequate to avoid helium liquefaction for tests in this Mach range. This 60-inch tunnel shared the test chamber and a control room with a similar 37-inch tunnel. Much of the research performed here, especially during its later years, involved turbulent boundary layers. With a declining interest in hypersonic research and budgetary constraints during the 1990s, NASA decided to demolish this tunnel in 1998.
[top] 37-Inch Mach 10 Helium Tunnel
Also known as the Mach 10 High-Reynolds Number Helium Tunnel and as one of the Hypersonic Aeroelasticity Tunnels, this tunnel opened in 1952. It was essentially a smaller, slower version of its 60-inch sibling, and it operated in the same manner using the same helium system. The two tunnel circuits shared a common control room. This tunnel ceased operations in the late 1970s, and it was demolished along with the 60-inch circuit in 1998.
[top] 2- by 3-Foot Low-Boundary-Layer Tunnel
This atmospheric, closed-circuit tunnel was installed as part of a modification to room H107 in Building 1247’s west wing. (Room B107 had been re-designated H107 during a prior modification to the space.) When originally installed in this room, it was oriented in a north-south direction, and it shared the space with the 60- and 37-inch helium tunnels until those tunnels were demolished. Langley considered relocating it to an extension of Building 1214, which housed the Basic Aerodynamics Research Tunnel (BART) in 1997, but rejected that option, even though the two tunnels performed similar work. Instead, the tunnel underwent a major rehabilitation during 2004 that rotated it 90 degrees to better fit in the H107 space. The tunnel is a self-contained device capable of speeds up to approximately 100 miles per hour, and it incorporates a honeycomb, four screens, and a 10:1 contraction ratio to reduce turbulence. The floor and ceiling of the 20-foot-long test section are adjustable to allow operators to set a desired longitudinal pressure gradient. Additionally, the tunnel is equipped with acoustic drivers upstream and downstream of the test section to excite the flow as needed.
[top] 20-Inch Mach 17 Nitrogen Tunnel
Previously known as the Hypersonic Nitrogen Tunnel, this conventional tunnel was built in 1964 in room B109. Nitrogen gas, flashed from a liquid storage tank, passed through an electric resistance heater at the nozzle’s inlet, continued through the tunnel’s axisymmetric nozzle and test section, and exited it through a diffuser and aftercooler into a vacuum sphere. Because of the benign nature of nitrogen and its low cost, the gas was vented to atmosphere after test runs and not recovered. Despite its name, the tunnel’s test section was shown as being only 17 inches in diameter in Langley facility résumés, though it may originally have had a larger test chamber and on open jet. This nitrogen tunnel was built to investigate how well a single gas could simulate air at hypersonic flight speeds. Unfortunately, the flow in this tunnel was more turbulent than desired, and nitrogen offered no clear advantages over air that justified its cost. Proposals to rectify the flow problems were not approved. With a declining interest in hypersonic research and budgetary constraints during the 1990s, NASA decided to close this tunnel about 1998 and subsequently demolish it in 2007.
[top] Arc-Heated Scramjet Test Facility
Originally known as the 4-Foot Hypersonic Arc Tunnel, this tunnel was built in room B111 in 1964 to support high-enthalpy hypersonic fluid mechanics research. (Enthalpy is a thermodynamic term for the total internal energy of a volume of gas, including its temperature and pressure, expressed as heat. Its English measurement unit is Btu/lbm.) The tunnel used an electric arc with a 10 to 20 megawatt direct-current power supply to heat dry inlet air from the central utilities system. The heated air then passed through an axisymmetric nozzle and accelerated into either a 2- or 4-foot-diameter test section (the core test diameter was about one-half that) and impinged on the model. The air then exhausted through an aftercooler and into the 100-foot-diameter vacuum sphere. Since a different nozzle length was needed for each test section, the heater and nozzle were mounted on a track that guided the necessary movement. It could generate speeds between Mach 8 and 18, with enthalpies between 1,500 and 6,000 Btu/lb.
This tunnel was converted into a facility for testing complete scramjet models in 1974 and re-named the Scramjet Test Facility, later refined into Arc-Heated Scramjet Test Facility (AHSTF), to distinguish it from combustion-heated scramjet tunnels in Building 1221. The conversion involved changes to the nozzle, model support hardware, and instrumentation, as well as the addition of a model fuel system, but its basic, arc-heated operation remained the same. Managed by the Hypersonic Air-breathing Propulsion Branch, it remains in active service, testing scramjet models approximately 8 by 10 inches in cross section at simulated flight speeds of Mach 4.7 – 8.0. Inlet air from a 5,000-pound-per-square-inch bottle field passes through an electric arc, where it is heated to as high as 4,600 Fahrenheit, accelerated through the nozzle into the test section, and, as before, exhausted through an aftercooler to the 100-foot-diameter vacuum sphere. Engine fuel is gaseous hydrogen, with a 20/80-percent silane/hydrogen mixture available to promote ignition. Run times are typically 10 – 60 seconds. During 2008, the AHSTF was reconfigured to run in a direct-connect mode, which simulates inlet conditions at the engine’s combustor for tests involving fuel ignition and flame stability.
[top] Hotshot Tunnel
The Hotshot Tunnel, built in 1960 and operational in November 1962, was an arc-heated, impulse tunnel. Being Langley’s first hotshot tunnel, setup and calibration proved arduous, with difficult problems to be solved in materials electrodes, insulators, connections, and instrumentation. It was built in room B115 primarily to perform force, pressure-distribution, and heat-transfer tests at Mach 20 and above. As with all hotshot tunnels, this tunnel operated by heating its test gas (air, nitrogen, or helium) in a small chamber at one end with an electric arc. A bank of 720 capacitors delivered an instantaneous 7,500-volt, 2 x 106-joule potential across two electrodes in the chamber, and the arc created heated the gas to about 5,000 Fahrenheit, which, in turn, caused the gas pressure to increase to approximately 10,000 pounds per square inch. This pressure burst a polyethylene terephthalate diaphragm and allowed the gas to accelerate through an asymmetric nozzle and pass through the test section into a 200-cubic-foot dump tank. Prior to the run, the entire tunnel downstream of the diaphragm had been evacuated to approximately 1 micron of mercury by mechanical and oil-diffusion pumps. Typical run times ranged between 30 and 120 milliseconds, which required ultra-high-speed instrumentation and control equipment. Data was recorded using high-speed oscillographs and magnetic tape.
This tunnel provided Langley researchers with experience operating non-conventional tunnels, and modifications eventually allowed some tests above Mach 30. While the results were useful, the high energy involved with the arc heater continued to pose problems and risk. After an accident seriously damaged this tunnel, it was demolished in 1969. No portion of it is known to have survived.
[top] 15-Inch Low-Turbulence Tunnel
The 15-inch Low-Turbulence Tunnel is a self-contained, closed-circuit tunnel that can produce very stable air flows up to about 88 miles per hour. Its test section consists primarily of clear panels, and it offers excellent optical access for laser velocimetry (LV) and particle-image velocimetry (PIV) measurements. Recent research involving active flow control devices to improve jet engine inlet performance in adverse conditions has relied heavily of the tunnel’s PIV capabilities. The tunnel remains in service.
[top] 20- by 28-Inch Shear-Flow Tunnel
The 20- by 28-Inch Shear-Flow Tunnel is an atmospheric, open-circuit tunnel with a top speed of approximately 100 miles per hour that was purchased as a self-contained unit from Aerolab. Intended primarily for fundamental boundary-layer research, a series of inlet screens and a large contraction ratio deliver air to the test section with very low freestream turbulence. The 15-foot-long test section features large windows on both sides and an adjustable ceiling for control of the pressure gradient through the full length of the test section. The large windows provide excellent optical access for laser velocimetry (LV) and particle-image velocimetry (PIV) measurements. This tunnel remains in service.
[top] 7- by 11-Inch Low-Speed Tunnel
The 7- by 11-Inch Low-Speed Tunnel is an atmospheric, open-circuit tunnel with a top speed of approximately 100 miles per hour that was purchased as a self-contained unit from Aerolab about 1965, initially installed in room B115, and moved into room D105 sometime later. (Room D105 earlier housed a 20-Megawatt Linear Plasma Accelerator used for magnetoplasmadynamics studies.) Initially intended as a pilot for the 14- by 22-Foot Subsonic Tunnel, it has been primarily utilized for fundamental research since 1970. It is now optimized for direct-drag measurements of flat panels, and it employs a linear air bearing drag balance. This tunnel is equipped with a variety of pitot and hotwire-type flow measurement instruments, as well as smoke-injection and smoke-wire capabilities for flow visualization. Its primary use has been for studies into drag reduction within turbulent boundary layers, but it achieved some unusual notoriety in 2008 when swimmers Michael Phelps and Natalie Coughlin made Olympic history wearing swimsuits made of a drag-reducing fabric developed in part through testing in this tunnel by Langley researcher Stephen Wilkinson. The tunnel remains in service.
[top] 12-Inch Mach 6 High-Reynolds Number Tunnel
Also known as the Mach 6 High-Pressure Tunnel, the 12-Inch Mach 6 High-Reynolds Number Tunnel entered service in 1967. It was a conventional tunnel that used heated dry air furnished by the facility and exhausted through an aftercooler into a 41-foot-diameter vacuum sphere to generate a speed of Mach 6. Electric resistance-type heaters heated the incoming air to a maximum temperature of about 540 Fahrenheit. This tunnel featured an axisymmetric nozzle into two interchangeable, 12-inch-diameter test sections. One was equipped with schlieren windows and a model-injection mechanism capable of handling models up to 4-feet long. The second test section was designed for investigations of boundary layers along the tunnel wall using a variety of measurement techniques. The tunnel, housed in room D106, was closed about 1998 and demolished in 2007 to make room for two acoustic research devices being relocated from other buildings in the West Area, the Curved-Duct Test Rig from Building 1218, and the Grazing-Flow Impedance Tube from Building 1287.
[top] 20-Inch Supersonic Wind Tunnel
The 20-Inch Supersonic Wind Tunnel (SWT) was originally designed and built at the Jet Propulsion Laboratory (JPL) in Pasadena, California, in 1948, a full decade before JPL became part of NASA. At the time, JPL, a unit of the California Institute of Technology, was heavily engaged in rocket engine development, and this tunnel was one of two it built to support that activity. After JPL became a unit of NASA, its hardware role gradually shifted from rocket engines to the development of unmanned spacecraft, drastically reducing its need for wind tunnels. By 1980, the laboratory needed the space they occupied for other facilities, so NASA looked to relocate them within the agency.
Robert L. Trimpi, a Langley researcher, realized that the 20-inch JPL tunnel could be useful at Langley, and he recommended that it be moved. Actually, only the core of the tunnel—its nozzle, test section, and diffuser—were moved to Virginia. JPL had powered the tunnels with dedicated air compressors that were not needed at the HFC, which could also furnish vacuum at the exhaust end. Between 1982 and 1986, Trimpi oversaw its move and installation in room D107. A new air-inlet section, enclosed in a room that filled part of the central hall, was built, and the diffuser exhaust was mated to a new duct with a valve that directed the flow either to atmosphere or to a 60-foot-diameter vacuum sphere. Langley named it the 20-Inch Supersonic Wind Tunnel.
This tunnel had a unique distinction. It was the first supersonic tunnel built that used flexible top and bottom walls to vary the speed. Supersonic nozzles must be precisely contoured for a specific speed, but JPL engineers had devised a nozzle that used a series of jacks to flex sheets of stainless steel and, thus, re-contour the nozzle for a range of speeds between Mach 1.4 and 5.0. Both sides of the nozzle retract for access to the nozzle and the forward portion of the 20- by 18-inch test section. Trimpi added an 8-foot-diameter settling chamber, along with a “quiet” valve and flow-conditioning section to supply stable air to the nozzle and, thus, help create a uniform flow through the core of the test section.
Models are typically sting-mounted on a support that allows pitch adjustment from 34 to -9.5 degrees and ±8.5 degrees in yaw. They are protected from startup and shutdown transient temperatures and loads by a plenum isolation door and a rapid injection capability of the support system. A variety of heat-transfer and static pressure instrumentation is available, plus laser velocimetry for flow-field measurements. In recent years researchers developed a way for the tunnel to operate subsonically as well, and it has proven useful for airfoil testing in the Mach 0.35 – 0.75 range. Maximum run times approach 30 minutes when the exhaust is to atmosphere. The tunnel received several modifications in 1994 to improve its reliability and ease of use, including a connection to the HFC’s 100-foot-diameter vacuum sphere that enables it to use the total volume of the 60- and 100-foot spheres for longer run times. The 20-Inch Supersonic Wind Tunnel has been a very productive facility at Langley, and it remains in active service.
[top] 20-Inch Mach 6 Tunnel
The 20-Inch Mach 6 Tunnel in room D108, opened in 1958 as the 20-Inch Hypersonic Tunnel, is a conventional tunnel utilized for aerodynamic and aerothermodynamic tests of proposed aerospace vehicles, and for the exploration of basic fluid dynamic phenomena, including boundary layer laminar-to-turbulent transition. The tunnel uses dry air furnished by the facility and heated by an electric resistance heated, and it exhausts through an aftercooler into a vacuum sphere, to the atmosphere (assisted by an air ejector), or a combination of the two. Its diffuser includes a moveable second minimum. The tunnel delivers a speed of Mach 6, with stable flow in a core test area measuring 12-inches square in its 20- by 20-inch test section. Models can be fixed on the floor, or sting mounted on an injection mechanism, which allows a pitch setting from 55 degrees to -5 degrees and a yaw range of 0 to -10 degrees. Run times vary from 2 to 20 minutes, depending on the choice of exhaust.
The results of tests conducted in this tunnel are often compared to those from tests in the 31-Inch Mach 10 and 20-Inch Mach 6 CF4 tunnels to more fully assess the effects of compressibility and real-gas aerothermodynamics under similar Reynolds number conditions. This tunnel performed a large number of tests during the Space Shuttle development program, and it is kept available during missions to investigate potential problems. The 20-Inch Mach 6 Tunnel is in service.
[top] Mach 6 Pilot Quiet Tunnel
Also known as the Nozzle Test Chamber, this facility was not actually a research tunnel per se, but rather a conventional device used primarily to develop a low-disturbance, or quiet, hypersonic nozzle. Constructed about 1995, and originally installed in room D108, it received heated air from the building’s central system and exhausted through an aftercooler to a vacuum sphere. The extended settling chamber ahead of the asymmetric nozzle measured 85 inches long and contained as many as 11 screens, including one formed out of steel wool, to eliminate turbulence. The nozzle contraction also featured an annular slot connected to a vacuum source to remove any remaining boundary-layer immediately ahead of the throat. The 19-inch-diameter nozzle exhausted into a larger test section, where an overhead model-injection device inserted the model once stable flow had been achieved. Air exited the test section through a conical collector and diffuser to a vacuum vessel. While complex to build and operate, the apparatus achieved very-smooth, low-turbulence flow at Mach 6, and its success has prompted additional developmental work by others in the field. This tunnel was relocated to room D114 in the late-1990s, after the removal of other equipment freed the space. After almost a decade of service, the Mach 6 Pilot Quiet Tunnel was dismantled in 2005 and donated to Texas A&M University in College Station, Texas, where it is currently being modified for a return to service.
[top] 18-Inch Mach 8 Variable-Density Tunnel
Opened in 1960 in room D115, the 18-Inch Mach 8 Variable-Density Tunnel, also known as the Mach 8 Variable-Density Hypersonic Tunnel and the 18-Inch Mach 8 Tunnel, is a conventional tunnel capable of producing a wide range of Reynolds numbers. It uses dry air heated by a two-stage heater that a control valve delivers to the settling chamber at 20 to 3,000 pounds per square inch. The heater’s first stage employs a circulating ethylene glycol fluid that heats the air to approximately 150 Fahrenheit. An electric resistance heater then raises the temperature to as high as 1,030 Fahrenheit. The settling chamber contains screens to stabilize the flow, which then passes through the axisymmetric nozzle and 18-inch-diameter test section. Depending on the operating pressure, the core test area measures between 4 and 14 inches in diameter. A model injection system raises the model, which can be up to 27 inches long, into the stabilized air stream. The sting has adjustments for pitch and yaw. The tunnel exhausts through a diffuser with a second minimum to the atmosphere or into a pair of vacuum spheres, 41 and 60 feet in diameter. This tunnel produces speeds between Mach 7.5 and 8.0, depending on pressure. The maximum run time to vacuum is about 90 seconds, but runs as long as 10 minutes are possible when exhausting to the atmosphere. This tunnel has largely been on standby since the late-1970s, and is scheduled fro demolition in 2013.
[top] 20-Inch Mach 8.5 Tunnel
Opened in 1961, the 20-Inch Mach 8.5 Tunnel was a conventional tunnel that generated the highest speed using air of all Langley tunnels. Housed in room D116, it used dry air heated by an electric resistance heater to 1,000 Fahrenheit. The settling chamber contained screens to stabilize the flow, which then passed through the axisymmetric nozzle and 21-inch-diameter test section. (Why “20-Inch” was chosen for its name is unknown.) The core test area measured 16 inches in diameter. A model injection system raised the model into the stabilized air stream. The sting had adjustments for pitch and yaw. The tunnel exhausted through a diffuser with a movable second minimum to the atmosphere or a vacuum sphere. The maximum run time to atmosphere was about 7 minutes and about 30 seconds to vacuum. This tunnel was demolished about 1980 to provide space for the Pilot Supersonic Low Disturbance Tunnel.
[top] 6- by 10-Inch Supersonic Low-Disturbance Tunnel
Originally built in 1988 as the Pilot Supersonic Low Disturbance Tunnel, this facility is a Mach 3.5 conventional tunnel with specific features intended to produce a low-turbulence, or “quiet” flow through the core of its test section. Using air as the test gas, its quiet flow is achieved using a combination of settling chamber devices, a boundary-layer extraction system, and a highly-polished, 2-dimensional nozzle with a boundary-layer bleed upstream of its throat. Although a boundary does form in the nozzle that ultimately generates a shock wave and downstream turbulence, the design produces a very quiet core in the shape of a rhombus 5 – 10 inches by 1.5 – 3.6 inches in size (the size varies with Reynolds number). Since this tunnel exhausts to the atmosphere, typical run times range from 15 to 30 minutes. This tunnel’s primary use has been in developing supersonic quiet-flow technology and computational methods. It currently sees limited use, but remains intact.
[top] Probe-Calibration Tunnel
The Probe Calibration Tunnel in room D118 is a conventional, open-jet pressure tunnel with three interchangeable nozzles, and it has adjustments for the independent control of pressure, temperature, and speed. Test section pressure can be varied from 0.13 to 10 atmospheres (2 – 146 psia), and stagnation temperature can be set from 0 to 200 Fahrenheit. Its three interchangeable nozzles provide a speed range of Mach 0.05 – 3.5. As its name indicates, this tunnel is used primarily to calibrate instrumentation used in the Hypersonic Facilities Complex’s other tunnels. This tunnel is in service.