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At least 343 records · Page 19

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NASA NTRS1986

Resonance prediction for slotted wind tunnel by the finite element method

A finite element approach is developed for predicting the so-called 'resonant' frequencies of subsonic wind tunnels with variously shaped cross sections. The resulting computer code has been applied to various wind tunnels. For example, the resonant frequencies for both the NASA Ames Research Center 6 x 6 ft wind tunnel (rectangular cross section) and the NASA Langley Research Center 16 x 16 ft Transonic Dynamics Tunnel (octagonal cross section) have been calculated. The results are believed to be more accurate than theoretical values used in the past for an equivalent rectangular cross section. The effect of a plenum chamber on the resonance is examined in detail. Application of the finite element approach to the plenum chamber, as it interacts with the test section, gives more accurate results than what would be obtained by assuming an open tunnel.

Lee, I.↗

NASA NTRS1987

Lumped-Parameter Representation of Wind Tunnel

Mathematical model of proposed wind-tunnel facility represents wind-tunnel circuit and associated equipment in terms of lumped-parameter components. Requires less computational effort and computing time than full three-dimensional aerodynamic computer analysis of system with many volume elements. Approximates distributed nature of wind tunnel well enough to simulate steady-state and transient behavior for analysis of proposed control subsystems and for training of operators. Lumped-parameter circuit model represents wind tunnel and associated equipment. Implemented on analog or digital computers to simulate wind-tunnel performance without risk to operators or equipment.

Krosel, Susan M.↗

NASA NTRS1987

Computational study of wind-tunnel wall effects on flow field around delta wings

This paper addresses wind-tunnel wall effects on delta-wing flow fields using the Free Vortex Sheet (FVS) theory in support of planned subsonic wind-tunnel tests. The configurations include several sizes of a 65-deg delta wing in the NASA Langley Research Center Low-Turbulence Pressure Tunnel (LTPT), and an aspect ratio 1 delta wing in the Delft University low-speed tunnel. Standard upflow correction methodology is extended to account for angle-of-attack and nonplanar effects. Blockage and streamline curvature corrections are not applied in the present investigation. Resulting corrections to the 65-deg delta flow field were good for model-to-tunnel span ratios up to 0.5 and angles of attack up to 30-deg, both for linear attached flow and nonlinear vortex flow. For the aspect ratio 1 delta wing, corrections to the vortex flow field for the effect of the averaged upflow angle were satisfactory but streamline curvature effects were larger.

Frink, Neal T.↗

NASA NTRS1988

Surface flow visualization of separated flows on the forebody of an F-18 aircraft and wind-tunnel model

A method of in-flight surface flow visualization similar to wind-tunnel-model oil flows is described for cases where photo-chase planes or onboard photography are not practical. This method, used on an F-18 aircraft in flight at high angles of attack, clearly showed surface flow streamlines in the fuselage forebody. Vortex separation and reattachment lines were identified with this method and documented using postflight photography. Surface flow angles measured at the 90 and 270 degrees meridians show excellent agreement with the wind tunnel data for a pointed tangent ogive with an aspect ratio of 3.5. The separation and reattachment line locations were qualitatively similar to the F-18 wind-tunnel-model oil flows but neither the laminar separation bubble nor the boundary-layer transition on the wind tunnel model were evident in the flight surface flows. The separation and reattachment line locations were in fair agreement with the wind tunnel data for the 3.5 ogive. The elliptical forebody shape of the F-18 caused the primary separation lines to move toward the leeward meridian. Little effect of angle of attack on the separation locations was noted for the range reported.

Fisher, David F.↗

NASA NTRS1988

Space shuttle phase B wind tunnel model and test information. Volume 2: Orbiter configuration

Archived wind tunnel test data are available for flyback booster or other alternate recoverable configurations as well as reusable orbiters studied during initial development (Phase B) of the Space Shuttle. Considerable wind tunnel data was acquired by the competing contractors and the NASA centers for an extensive variety of configurations with an array of wing and body planforms. All contractor and NASA wind tunnel test data acquiredin the Phase B development have been compiled into a database and are available for applying to current winged flyback or recoverable booster aerodynamic studies. The Space Shuttle Phase B Wind Tunnel Database is structured by vehicle component and configuration type. Basic components include the booster, the orbiter, and the launch vehicle. Booster configuration types include straight and delta wings, canard, cylindrical, retroglide, and twin body. Orbiter configuration types include straight and delta wings, lifting body, drop tanks, and double delta wings. Launch configration types include booster and orbiter components in various stacked and tandom combinations. The digital database consists of 220 files of data containing basic tunnel recorded data.

Glynn, J. L.↗

NASA NTRS1989

Survey Of Wind Tunnels At Langley Research Center

Report presented at AIAA 14th Aerodynamic Testing Conference on current capabilities and planned improvements at NASA Langley Research Center's major wind tunnels. Focuses on 14 major tunnels, 8 unique in world, 3 unique in country. Covers Langley Spin Tunnel. Includes new National Transonic Facility (NTF). Also surveys Langley Unitary Plan Wind Tunnel (UPWT). Addresses resurgence of inexpensive simple-to-operate research tunnels. Predicts no shortage of tools for aerospace researcher and engineer in next decade or two.

Bower, Robert E.↗

NASA NTRS1987

Support of the eight-foot high-temperature tunnel modifications project

An ultrasonic level sensor was developed to measure the liquid level in a storage vessel under high pressures, namely up to 6000 psi. The sensor is described. A prototype sensor was installed in the cooling-water storage vessel of the Eight-Foot High-Temperature Tunnel. Plans are being made to install the readout instrument in the control room, so that tunnel operators can monitor the water level during the course of a tunnel run. It was discovered that the sensor will operate at cryogenic temperatures. Consequently, a sensor will be installed in the modified Eight-Foot High-Temperature Tunnel to measure the sound speed of liquid oxygen (LOX) as it is transferred from a storage vessel to the tunnel combustor at pressure of about 3000 psi. The sound speed is known to be a reliable indicator of contamination of LOX by pressurized gaseous nitrogen, which will be used to effect the transfer. Subjecting the sensor to a temperature cycle from room temperature to liquid nitrogen temperature and back again several times revealed no deterioration in sensor performance. The method using this sensor is superior to the original method, which was to bleed samples of LOX from the storage vessel to an independent chamber for measurement of the sound speed.

Hodges, Donald Y.↗

NASA NTRS1989

Investigation of the flow in the diffuser section of the NASA Lewis icing research tunnel

The flow in the diffuser section of the Icing Research Wind Tunnel at NASA Lewis Research Center is investigated using both tunnel calibration measurements and numerical simulation techniques. Local pressure and temperature measurements are made to establish velocity and temperature profiles in the diffuser of the tunnel. These profiles are compared with similar measurements made prior to renovating the equipment which generates the tunnel's icing cloud. This comparison indicates the manner in which this change affected the flow. The measured data were also compared with a numerical simulation of the flow to help understand how such changes may favorably alter the tunnel flow.

Addy, Harold E., Jr.↗

NASA NTRS1989

Investigation of the flow in the diffuser section of the NASA Lewis Icing Research Tunnel

Addy, Harold E., Jr.↗

NASA NTRS1988

Cryogenic wind tunnel research - A global perspective

The development of cryogenic wind tunnels is reviewed and 13 cryogenic wind tunnels currently operating in England, France, Germany, Japan, and the U.S. are described. A table illustrating the characteristics of these tunnels is presented, including test gases, test section sizes, speed ranges, stagnation pressure and temperature, and running time. The research conducted using the various wind tunnels is outlined and the operation of each of the tunnels is considered.

Dress, D. A.↗

NASA NTRS1989

NbN/MgO/NbN SIS tunnel junctions for submm wave mixers

The authors report on the fabrication and testing of all-refractory NbN/MgO/NbN SIS (superconductor-insulator-superconductor) tunnel junctions for use as high-frequency mixers. Progress in the development of techniques for the fabrication of submicron-area tunnel junctions is described. Junction structures which have been investigated include mesa, crossline, and edge geometries. Using reactive sputtering techniques, NbN tunnel junctions with critical currents in excess of 104 A/sq cm have been fabricated with Vm values as high as 65 mV and areas down to 0.1 sq micron. Specific capacitance measurements on NbN/MgO/NbN mesa-type tunnel junctions give values in the range 60-90 fF/sq micron. These SIS tunnel junctions have been integrated with antennas and coupling structures for mixer tests in a waveguide receiver at 207 GHz. Preliminary mixer results are reported.

Stern, J. A.↗

NASA NTRS1989

Theoretical and experimental study of flow-control devices for inlets of indraft wind tunnels

The design of closed circuit wind tunnels has historically been performed using rule of thumb which have evolved over the years into a body of useful guidelines. The development of indraft wind tunnels, however, has not been as well documented. The design of indraft wind tunnels is therefore generally performed using a more intuitive approach, often resulting in a facility with disappointing flow quality. The primary problem is a lack of understanding of the flow in the inlet as it passes through the required antiturbulence treatment. For wind tunnels which employ large contraction ratio inlets, this lack of understanding is not serious since the relatively low velocity of the flow through the inlet treatment reduces the sensitivity to improper inlet design. When designing a small contraction ratio inlet, much more careful design is needed in order to reduce the flow distortions generated by the inlet treatment. As part of the National Full Scale Aerodynamics Complex Modification Project, 2-D computational methods were developed which account for the effect of both inlet screens and guide vanes on the test section velocity distribution. Comparisons with experimental data are presented which indicate that the methods accurately compute the flow distortions generated by a screen in a nonuniform velocity field. The use of inlet guide vanes to eliminate the screen induced distortion is also demonstrated both computationally and experimentally. Extensions of the results to 3-D is demonstrated and a successful wind tunnel design is presented.

Ross, James C.↗

NASA NTRS1990

The Langley 14- by 22-Foot Subsonic Tunnel: Description, Flow Characteristics, and Guide for Users

The Langley 14- by 22-foot Subsonic Tunnel is a closed circuit, single-return atmospheric wind tunnel with a test section that can be operated in a variety of configurations (closed, slotted, partially open, and open). The closed test section configuration is 14.5 ft high by 21.75 ft wide and 50 ft long with a maximum speed of about 338 ft/sec. The open test section configuration has a maximum speed of about 270 ft/sec, and is formed by raising the ceiling and walls, to form a floor-only configuration. The tunnel may be configured with a moving-belt ground plane and a floor boundary-layer removal system at the entrance to the test section for ground effect testing. In addition, the tunnel had a two-component laser velocimeter, a frequency modulated (FM) tape system for dynamic data acquisition, flow visualization equipment, and acoustic testing capabilities. Users of the 14- by 22-foot Subsonic Tunnel are provided with information required for planning of experimental investigations including test hardware and model support systems.

Gentry, Garl L., Jr.↗

NASA NTRS1990

Aerothermodynamics and transition in high-speed wind tunnels at NASA Langley

The evolutionary development of subsonic, supersonic, and hypersonic wind tunnels for the study of aerodynamic, aerothermodynamic, and fluid-dynamic characteristics of the flow about models, including transition from laminar to turbulent boundary layers, is discussed. Currently, three supersonic and seven hypersonic wind tunnels are operational at Langley, and two additional tunnels are scheduled to become operational by 1990. In the present work, an effort is made to provide a 'tour'of selected supersonic and hypersonic wind tunnels at NASA-Langley used for aerodynamic and aerothermodynamic testing of models, and to present the evolution of quiet-tunnel technology at this facility over the last decade. It is noted that upgrades to the hypersonic facilities complex are underway in order to provide the high flow quality and improved data accuracy required to calibrate advanced computational fluid-dynamic computer codes. Also to be provided are increased productivity required for configuration development and improved reliability to support major hypersonic programs in an efficient and timely manner.

Beckwith, I. E.↗

NASA NTRS1991

Description and evaluation of an interference assessment for a slotted-wall wind tunnel

A wind-tunnel interference assessment method applicable to test sections with discrete finite-length wall slots is described. The method is based on high order panel method technology and uses mixed boundary conditions to satisfy both the tunnel geometry and wall pressure distributions measured in the slotted-wall region. Both the test model and its sting support system are represented by distributed singularities. The method yields interference corrections to the model test data as well as surveys through the interference field at arbitrary locations. These results include the equivalent of tunnel Mach calibration, longitudinal pressure gradient, tunnel flow angularity, wall interference, and an inviscid form of sting interference. Alternative results which omit the direct contribution of the sting are also produced. The method was applied to the National Transonic Facility at NASA Langley Research Center for both tunnel calibration tests and tests of two models of subsonic transport configurations.

Kemp, William B., Jr.↗

NASA NTRS1991

Saltation threshold detection in a wind tunnel by the measurement of the net electrostatic charge

The Mars surface wind tunnel (MARSWIT) is an open circuit wind tunnel used for aeolian studies and is located inside a large vacuum chamber allowing testing at Martian surface atmospheric pressure. Since direct access is not available to the tunnel during operation at low pressure, a remote method of saltation detection is needed. The bed is observed by means of closed circuit video, but it is often difficult to determine the initiation of threshold. The measurement by means of an electrometer of the net electric charge produced by the saltating particles has provided a reliable means of saltation threshold detection. Saltating particles become charged several ways, both in wind tunnels and in a natural environment. The most significant of these methods are tribo-charging and contact charging, which always occur. Fracture charging may also occur under the high velocities associated with particle transport on Mars or under simulated Martian conditions. Detection in MARSWIT is achieved by allowing the saltating particles to impinge on a planar conducting surface normal to the flow that is connected to ground through a Keithly electrometer. The signal from the electrometer is connected to a strip chart recorder along with the analog signal from the pitot tube transducer that is used to determine the wind velocity in the tunnel. Thus, a record of wind velocity and the initiation of particle saltation is conveniently displayed together. While both positive and negative charges are produced during saltation, this method measures only the net charge; thus the charge may be either positive or negative depending upon the particles being tested, the size and size distribution of the test material, and the wind velocity. This has proven to be a very trustworthy and sensitive method of saltation threshold detection, being especially useful with the smaller sized particles which are the most difficult to observe visually.

Leach, Rodman N.↗

NASA NTRS1987

Cryogenic wind tunnels. I

The basic principles of cryogenic wind-tunnel operation are presented, and a typical cryogenic wind tunnel is described. Low-speed cryogenic wind tunnels are considered, along with some experiments conducted in these tunnels. Focus is placed on real-gas effects including condensation and thermal and caloric imperfections. The operating limits set by the saturation boundaries of nitrogen and air are analyzed, and the consequences of thermal and caloric imperfections on both isentropic and normal-shock flow in nitrogen are considered. The extension of analytical real-gas studies, including both laminar and turbulent boundary layers is covered. It is concluded that the deviation of the nitrogen boundary-layer parameters from their ideal-gas values are small, and that large real-gas effects will not be a factor in cryogenic tunnel simulation of the complex flows met in flight.

Kilgore, Robert A.↗

NASA NTRS1990

High-speed quiet tunnels

The adverse effect of wind-tunnel noise on boundary-layer transition is considered, and the development of Pilot Quiet Tunnels exhibiting low noise levels in upstream regions of the test rhombus to high values of the stream unit Reynolds number is covered. Advances in quiet nozzle and tunnel designs are discussed, including a new Mach-8 nozzle and modifications to an existing conical nozzle in one of the helium tunnels at NASA Langley. Attention is focused on the final engineering design of a large-scale high-speed low-disturbance tunnel expected to accommodate nozzles of various lengths with Mach numbers ranging from 2 to 6.

Beckwith, Ivan E.↗