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Low Turbulence Pressure Tunnel

NASA Langley Research Center
The Low-Turbulence Pressure Tunnel (LTPT) is a unique facility that provides flight Reynolds number testing capability for two-dimensional airfoils and a low turbulence environment for laminar flow control and transition studies and the testing of low-drag airfoils.
Test Section and Performance
 Low Turbulence Pressure Tunnel Characteristics
The Langley Low-Turbulence Pressure Tunnel (LTPT) is a single-return, closed-circuit tunnel that can be operated at stagnation pressures from 1 to 10 atmospheres. The test section is rectangular (3-ft wide by 7.5-ft high by 7.5-ft long) with a contraction ratio of 17.6:1. The chord length for a typical airfoil tested in the facility is approximately 2 ft. There are provisions for sidewall boundary layer control through tangential blowing through tubes located on model endplates or passive suction through porous endplates vented to atmosphere. There is also the capability for testing three-dimensional models with 6-component force balances mounted on a centerline strut. The turbulence levels of the LTPT are very low due to the large contraction ratio and fine-mesh anti-turbulence screens.
Test section size, ft
3 x 7.5 x 7.5
Mach number
0.05 - 0.5
Reynolds number, /ft
0.4 - 15 x106
Total pressure, psia
14.7 - 150
Dynamic pressure, psi
0.1 - 5.0
Total temperature, °F
60 - 120
Run time
Continuous


High-Pressure Air and
Cooling Capability
A 350-psi off site air supply system provides dry compressed air to the facility. On site storage tanks are utilized with an air capacity of 8000 ft3 at 300 psi. The heat exchanger upstream of the anti-turbulence screens can use either for cooling or heating the airflow.

X34 model
Metal model of the X-34 reusable launch vehicle being tested in the LTPT
Line Drawing
 Model Observation
Photographic and video coverage of the test section is possible from the sidewall and ceiling windows. Video images of the model can be recorded on VHS recorders.
Instrumentation
For 2-dimensional single or multi-element airfoil testing, the model is mounted by endplates to unique model-support and force-balance system. For 3-dimensional model testing, a wide variety of internal strain-gage balances can be used for force and moment measurements. The electronically scanned pressure (ESP) System provides highly accurate steady-state pressure measurements of the model and the facility. Airfoil surface boundary layers (BL) can be measured with a BL traverser mechanism mounted on the model endplate. 		Data Acquisition and Processing
The standard data acquisition system consists of an analog-to-digital converter, capable of acquiring 128 channels of analog data (up to 1000 Hz) and 40 channels of digital data, and a UNIX computer. Final data is reduced on a separate UNIX workstation. For data analysis, the facility provides UNIX and Macintosh computers. Customer supplied computers can be networked to the data reduction system if desired. Secure data links are available for classified projects. 		Facilities Available to Users
A model build up bay is provided at the facility for build up of models. Also, a calibration area provides instrumentation and propulsion air systems for further calibrations that may be required to quantify deflection constants.

Safety and Design Criteria
Langley's LHB 1710.15 Wind Tunnel Model System Criteria is the guideline for model design and fabrication. Model installation and any exceptions to this document must have the approval of the Safety Head on a case-by-case basis to assure personnel and tunnel hardware are not exposed to risk.
Model Supports
 Test Techniques
A high-lift model support and three-component force balance system is provided for testing both single-element and multiple-element airfoils for 2-dimensional testing. For 3-dimensional testing, sting mounted models are attached to an arc-sector support system. The support system also includes a mechanized roll coupling.

3D Testing Model
Sketch of 3-D testing model support system 		Various oil or paint flow techniques are available to investigate transition or separation locations on the model, as well as sublimating chemicals. Pressure sensitive paint (PSP) techniques have been developed to acquire global surface pressure measurements also. Acoustic measurements with a focused microphone array that is mounted in the test section have been successful in determining noise from high-lift airfoils. In addition, two- and three-component laser velocimetry measurements can be measured in the test section.
Type of Testing
 Test Request Procedures

McDonnell-Douglas airfoil model in test section 		The LTPT has been used for 2-dimensional and 3-dimensional testing of airfoils including multi-element, high-lift, basic research, and theory validation. Capabilities include 3-dimensional model testing, high-lift model support and balance system, sidewall boundary-layer control system, excellent flow quality, and boundary layer and wake traverser systems.

LTPT's capabilities of low disturbance, low Mach numbers, variable density testing, high-lift, multi-element airfoil testing at flight Mach and Reynolds numbers are unique in the U.S. and the world.

The high Reynolds number capability anchors the low subsonic range, which in combination with the 0.3M Transonic Cryogenic Tunnel and the National Transonic Facility provide an unparalleled capability over the subsonic to transonic Mach number range. In addition, this tunnel is ideal for preliminary aerodynamic configuration screening because of low operational cost and relatively inexpensive models, which are properly sized for testing in both the 16-Foot Transonic Tunnel and the Unitary Plan Wind Tunnel. Therefore, configurations can be quickly evaluated with one model to a Mach number of 4.7 		The first step of the test process is to submit a test request form. The form can be filled out electronically or printed for mailing at the NASA Langley aero Compass website. A posttest questionnaire is also available at this site. Our customers are encouraged to provide feedback to the facility for our continuous improvement process.


Energy efficient transport (EET) semi-span flap model installed in LTPT
Document Version 1.0
Trademark Disclaimer:
The use of trademarks or names of manufacturers in this report is for accurate reporting and does not constitute an official endorsement, either expressed or implied, of such products or manufacturers by the National Aeronautics and Space Administration.
For more information contact:
The Low Turbulence Pressure Tunnel Manager -- NASA Langley Research Center -- Hampton, Virginia 23681-2199
phone: 757-864-3358 | fax: 757-864-8918 | e-mail: wte+fm_ltpt@larc.nasa.gov
NASA Official Responsible For Content: Pete Jacobs
Page Curator: Lori Rowland
Date Last Updated: 07/01/08

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