Low Turbulence Pressure Tunnel

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Facility 582A
Building 582A

Center: Langley Research Center
Location: Hampton, Virginia
Year Built: 1940
Historic Eligibility: National Register Eligible
Important Tests: Aircraft Icing, Airfoils, X-1, F-100, F-111, F-14, F-15 C-5A, Saturn, Apollo, Space Shuttle

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[top] History

When the Langley Variable Density Tunnel (VDT) was put into operation in 1922, its unique capability to test in pressurized conditions up to 20 atmospheres provided unprecedented aerodynamic data and made Langley a world-class aerodynamic research laboratory. This breakthrough facility could more accurately simulate flight conditions during tests of small-scale models than any other tunnel in the world. Langley quickly applied the tunnel to studies of the aerodynamic behavior of a variety of shapes including dirigibles, airplanes, and airfoils. The airfoil research, in particular, proved to be an extremely important contribution to the state of the art (see more on airfoils).

Unfortunately, while the VDT provided data in good agreement with flight test results for certain airfoil characteristics such as maximum lift, the levels of drag predicted by the tunnel testing were not in agreement with flight. Langley researcher Eastman Jacobs of the VDT staff had recognized that airstream turbulence in the VDT would be an issue, even during its early design stage. Artificial turbulence created by drive systems and flow quality shortcomings in wind tunnels can cause erroneous measurements in aerodynamic drag and other characteristics. Turbulence can affect the properties of the aerodynamic boundary layer (the thin layer of air adjacent to aircraft surfaces) which in part determines whether the airflow over components such as airfoils is laminar or turbulent. Jacobs’ concern was stimulated by two factors. First, he recognized that the geometry of the VDT was not conducive to low turbulence—in fact, the VDT had the highest levels of turbulence of any Langley tunnel at the time. Lowering the airstream turbulence requires a tunnel with a large contraction ratio (the ratio of settling-chamber to test-section cross-sectional areas) and flow-smoothing screens, and the VDT did not use either concept. The second factor of interest to Jacobs was that his emerging excitement for research on new low-drag airfoil shapes known as laminar flow airfoils required low turbulence levels for meaningful wind-tunnel studies. Aerodynamic drag of laminar flow airfoils is much less than that of conventional turbulent airfoils. Jacobs began an aggressive campaign to acquire a new wind tunnel capable of operation with extremely low levels of turbulence in its test section airstream.

Jacobs’ request for the construction of a new tunnel with "vanishingly low" turbulence levels was not accepted by Langley’s management, based in part on technical doubts over the necessity of such a facility by noted technical experts at Langley including Theodore Theodorsen. In addition, management believed that Congressional approval for the envisioned tunnel would be difficult to obtain based on the vague technical factors involved. However, aircraft icing problems were a high-priority issue in the NACA mission at the time, and Jacobs and Ira Abbott jointly designed an “icing tunnel” which had the same dimensions and layout as a desirable low-turbulence tunnel. Using this ploy, a full-scale model tunnel of a low-turbulence tunnel design was built in building 583 as the NACA Ice Tunnel with the stated purpose of investigating ice formation on aircraft components. In reality, it served the purpose of evaluating the revolutionary contraction and screening concepts required for low turbulence. The single-return, closed-throat tunnel was built of wood with a sheet steel lining. The Ice Tunnel became operational in June 1938 as an atmospheric (unpressurized) tunnel and served its alleged purpose with a few rapid investigations of icing, then its refrigeration equipment was removed and the tunnel was converted with arrays of honeycomb and screens to reduce the turbulence levels to extremely low levels. The tunnel was subsequently renamed the Langley Two-Dimensional Low Turbulence Tunnel (LTT). The highly successful operation of the model tunnel led to preparations to build a pressurized low turbulence tunnel to be known as the Langley Two-Dimensional Low Turbulence Pressure Tunnel (LTPT).

Authorization for the LTPT was granted in 1938 and the facility was constructed in Building 582A, becoming operational in May 1941. The tunnel had a test section 7.5' high by 3 ' wide and 7.5' in length. Its heavy steel plate structure could be pressurized to 10 atmospheres. The LTPT had a contraction ratio of 17.6 to 1 and 11 screen elements designed to smooth the airflow by breaking up eddies provided unprecedented low levels of turbulence. A 13' fan with 20 blades driven by a 2,000 horsepower motor provided test speeds up to about 380 mph (Mach 0.5). The flow circuit of the tunnel was built with curved sections rather than conventional 90° turns to minimize structural stress concentrations at the high air pressures used. Large splitter vanes were also used for structural reasons rather than flow control. Another unique feature of the tunnel was a metal sun shade over the top of the shell to reduce differences in temperatures between the upper and lower parts of the airstream due to solar heating. Differential heating of the airstream had been found to cause turbulence in preliminary testing of a smoke-flow tunnel. An airlock was provided to allow access to the test chamber and test section at pressures greater than atmospheric.

Compressed Air Wroker

An interesting sidebar to the operation of the tunnel is the NACA Medical Recompression Chamber. The test crew in this tunnel, as well as a few others, was subjected to high pressures during operations and so had to go through a depressurization process. During the war years, technicians wore diving bell suits while the tunnel was at alternate pressures. Before the high pressure air connection from the West Side, it would take days to depressurize. Instead of waiting several days to do a model configuration change, a person would go through the air lock and into the pressurized test section to work on the model. Even data acquisition was by observation of gages and manometers while inside the pressure vessel.After the work was completed, the person would go through the air lock again and go to a decompression chamber. For more on this, Mystery_Archives_2010#January_2010 Click Here.

Modified blade removed for salvage
The political and economic atmosphere during construction of the tunnel is apparent in the choice of some of the construction materials. Several parts from P-38 aircraft were utilized as components in the facility. One particular example is the use of the aircraft propellers as fan blades. Originally, the NACA attempted to power the LTPT with unmodified P-38 propeller blades. The original blades could not absorb the power of the drive system and added too much turbulence to the airflow. This was attributed to the rounded tips of the P-38. The blades were modified by cutting the tips off. The solution was successful, and the modified blades continued to serve the tunnel until it was closed and the blades were removed for salvage as historic artifacts.

At the time of its introduction, the LTPT had the lowest turbulence levels of any wind tunnel in the world. Initially test programs in the new facility focused on further development of low-drag airfoils (NACA 6-series airfoils) that were incorporated into many U.S. military aircraft during World War II (the first laminar-flow airfoil that was used by the P-51 Mustang had been based on earlier data from the LTT). Coupled with extensive results from other facilities including the VDT and LTT, data from the LTPT were cataloged by Abbott and Von Doenhoff in a publication which became the “Bible” of airfoil information for many generations in the aeronautics community.

The LTPT was briefly converted for use with Freon in 1948 and was later modified with slotted walls to permit transonic testing in 1953, but neither of the modifications proved to be successful. After 1955 the LTPT served as a pressure vessel for the Langley 26" Transonic Blowdown Tunnel (TBT) located in nearby Building 583 (the previous site of the LTT). The TBT had been put into operation in 1950. The LTPT continued to be used as a pressure reservoir until the mid 1960s.

In the 1970s Richard Whitcomb's highly successful research on transonic supercritical airfoils and wings had stimulated the development of airfoils for low- and medium speed vehicles such as business jets and personal-owner general aviation aircraft. As part of a major Langley program on these topics, the LTPT was reactivated in the early 1970s when interest in the new airfoils peaked.

The LTPT underwent a major overhaul between December 1979 and March 1982. The two main objectives of the rehabilitation work were to restore and improve the flow quality required for laminar-flow research and to provide a two-dimensional model-support and force-balance for testing airfoils. During the overhaul activities the original anti-turbulence screens and a cooling coil used to remove the heat put into the airstream during operations were replaced. In addition to the model support and balance modifications, a sidewall boundary-layer control system was added as well as a remote-controlled survey apparatus and a new data acquisition system.

Turbulence measurements made in the test section after the modifications were completed were about the same as measurements made after initial operations began in 1941.

Research applications in the LTPT included extensive contributions of new airfoil designs, more efficient high-lift flap systems, the first experiments with active laminar-flow-control concepts, and basic studies of flow phenomena at high Reynolds numbers. Aerodynamic studies of specific aerospace vehicles have contributed to the development of the X-1, F-100, F-111, F-14, F-15 and C-5A aircraft; and the Saturn, Apollo and Space Shuttle spacecraft. Late research had focused on problems of efficiently integrating engines into airframes for better performance of commercial and military aircraft.

In 2006, the drive motor of the LTPT burned, resulting in termination of operations. A decision to deactivate the tunnel was made as no funds were available to refurbish it. The LTPT Complex was demolished in 2014. To see a list of parts that were salvaged from the tunnel, see Salvage List.

[top] References

Summary of airfoil data (1945): NASA Technical Report No. 313: Drag and Cooling with Various Forms of Cowling for a "Whirlwind" Radial Air-Cooled Engine-I by Fred. E. Weick.

Modifications and calibration of the LTPT (1984): NASA Reference Publication 1129: STARS--A General-Purpose Finite Element Computer Program for Analysis of Engineering Structures by K. K. Gupta

Origin of fan blades from interviews by Joseph Chambers with retired researchers Ken Pierpont and William Sewall on 21 October 2013.

[top] Demolition Questionnaire

[top] Photos

[top] Construction

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[top] Interior

[top] Equipment and Repairs

[top] Models and Tests

[top] Group and Social Events

[top] Salvage

[top] Demolition

Demolition of the interior of the building began in the fall of 2013. The following photos were captured by Kevin Schrock with All Phase Services, one of the demolition contractors. These show some of the items that he found more interesting.

Additional photos taken in Spring and early Summer 2014 show the exterior demolition in progress:

[top] Charts

[top] Interviews

Ken Pierpont and His Career

[top] Films

NACA-Era:B-36 (Revised) Outboard Nacelle

NACA-Era: Tuft Studies of the G-17

NACA-Era: High Speed Air Flow for Airfoils

1945: Investigation of the 1/14 scale Outboard Nacelle for the XB-36 Airplane

Air Foils and The Low Turbulence Pressure Tunnel

[top] Documents

[top] Research Papers

Preliminary Investigation in the NACA Low-Turbulence Tunnel of Low-Drag Airfoil Sections Suitable for Admitting Air at the Leading Edge. Albert E. von Doenhoff and Elmer A. Horton. 1942. WR-L-694.

Summary of Airfoil Data. Ira H. Abbott, Alber E. von Doenhoff. and Louis S. Stivers, Jr. 1945. TR-824.

The Langley Two-Dimensional Low-Turbulence Pressure Tunnel. Albert E. von Doenhoff and Frank T. Abbott. May 1947. TN-1283.

Calculation of Tunnel-Induced Upwash Velocities for Swept and Yawed Wings. S. Katzoff and Margery Hannah. 1948. TN-1748.

Studies of the Use of Freon-12 as a Wind Tunnel Testing Medium. Albert E. von Doenhoff, Albert L. Braslow, and Milton A. Schwartzberg. 1953. TN-3000.

An Analytical Evaluation of Airfoil Sections for Helicopter Rotor Applications. Gene J. Bingham. 1975. TN-D-7796.

Low-Speed Wind-Tunnel Tests of 1/9-Scale Model of a Variable-Sweep Supersonic Cruise Aircraft. H. Clyde McLemore, Lysle P. Parlett, and William G. Sewall. 1977. TN-D-8380.

An Exploratory Investigation of the Effect of a Plastic Coating on the Profile Drag of a Practical-Metal-Construction Sailplane Airfoil. Dan M. Somers and Jean M. Foster. 1979. TM-80092.

Two-Dimensional Aerodynamic Characteristics of an Airfoil Designed for Rotorcraft Application. Gene J. Bingham, Kevin W. Noonan, and William G. Sewall. 1981. TP-1965.

6X19 Inch Application of a Transonic Similarity Rule William Sewall. 1982.

Recent Modification and Calibration of the Langley Low-Turbulence Pressure Tunnel. Robert J. McGhee, William D. Beasley, and Jean M. Foster. 1984. TP-2328.

Dynamic Flow Quality Measurements in the Langley Low Turbulence Pressure Tunnel. P. Calvin Stainback and F. Kevin Owen. 1984. AIAA Paper.

Langley Research Center's Low Turbulence Pressure Tunnel. P. Calvin Stainback, Robert J. McGhee, William D. Beasley, and Harry L. Morgan, Jr. 1986. (paper on the history and operating characteristics).

1986 Recent Uses of Low-Turbulence Pressure Tunnel

1987 Excerpt on Tunnel from Engineer in Charge

Structural Integrity of Wind Tunnel Wooden Fan Blades. Clarence P. Young, Jr., Robert T. Wingate, Kenneth W. Mort, James R. Rooker, and Harold E. Zager. 1991. TM-104059.

Evaluation of Tunnel Sidewall Boundary-Layer Control Systems for High-Lift Airfoil Testing. K. Paschal, W. Goodman, R. McGhee, B. Walker, and Peter A. Wilcox. 1991. AIAA Paper 91-3243.

A Wind Tunnel Study of Icing Effects on a Business Jet Airfoil. Harold E. Addy, Jr., Andy P. Broeren, Joseph G. Zoeckler, and Sam Lee. 2003. NASA TM 2003-212124 and AIAA 2003-0727.

Tests of an NACA 66, 2-216, a=0.6 Airfoil with a Slotted and Plain Flap. 1943 advance report by Milton Davidson and Harold R. Turner, Jr. for North American Aviation, Inc.

Wind Tunnel Investigation if a Beveled Aileron Shape Designed to Increase the Useful Deflection Range. 1944 NACA report by R.T. Jones and W.J. Underwood for the Army Air Forces, Material Command.

[top] General Building Documentation

1939 Drawings

1940 Three Dimensional Wind Tunnel

1942 Low-Turbulence Pressure Tunnel Details and Costs

1946 Specifications for Designing and Installing Freon-12 Equipment

1965 Real Property Record

1966 Facility Resume

1974 Quick Facts on Low-Turbulence Pressure Tunnel

1974 Characteristics

1977 Summary of the history of the LTPT Complex

1978 Floor plan

1980 Floor plan Section

1981-1982 Boundary Layer Removal System Correspondence

1983 Boundary Layer Control System Installation Progress Schedule Report

1988 Floor Plan Changes

1990 Facility Resume

1991 Jesse Midgett LTPT Work Records

1992 Letter to Virginia Air & Space Center Promoting Importance of the Low-Turbulence Pressure Tunnel

1994 Installation of a Boundary Layer Control System for the LTPT

1994 Application and AWS Historical Welded Structure Award

1997 Facility Details for Low-Turbulence Pressure Tunnel

1998 LTPT Promotional Brochure

Calibration of LTPT Semispan Balance for Two Dimensional Tests


Application to Use the Tunnel

Information Pamphlet

Photo Log

Special Achievement Citation for Group Accomplishments

2010 Historic American Engineering Record No. VA-118-F

[top] Researcher Notes

1939 Test 33 - NACA 0012 Airfoil Boundary Layer Surveys

1940 Tests 155 & 156 - Use of Slots in Tunnel Wall to Reduce Three-Dimensional Effect

1974 Shuttle Orbiter Base Drag Model Modification Documents

Calculation of Boundary Layer Thickness Along Test Section Walls

1996 Model Support Apparatus Notes

Freon Calibration Charts

Freon Operation Charts

Freon Operation Notes

Freon-12 Calculation Notes

Freon-12 Data Charts

Freon-12 Equations Notes

Freon-12 Graphs

Freon-12 Notes

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