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At least 109 records · Page 6

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NASA NTRS1975

Experimental investigation of supersonic flow past double-wedge configurations

Viscous-inviscid interactions characteristic of those which occur when the fuselage-generated shock wave interacts with the wing-generated shock wave of a shuttle orbiter were studied experimentally. Surface-pressure measurements and schlieren photographs were obtained to define the flowfield generated when a Mach 4.97 stream encounters a double-wedge configuration. The deflection angles for the two wedge surfaces were such that the shock interaction pattern was either a Type-V pattern or a Type-VI pattern, as defined by Edney. The correlation between the present data and the theoretical solution for the Type-VI solution is satisfactory. The correlation between the measured Type-V shock-interaction pattern and the theoretical solution is satisfactory up to the interaction region. Downstream of the interaction the Type-V data depend primarily on the shape of the leading-edge shock wave.

Bertin, J. J.↗

NASA NTRS1976

An experimental investigation of supersonic flow past a wedge-cylinder configuration

An experimental investigation of supersonic flow past double-wedge configurations was conducted. Over the range of geometries tested, it was found that, while theoretical solutions both for a Type V pattern and for a Type VI pattern could be generated for a particular flow condition (as defined by the geometry and the free-stream conditions), the weaker, Type VI pattern was observed experimentally. More rigorous flow-field solutions were developed for the flow along the wing leading-edge. Solutions were developed for the three-dimensional flow in the plane of symmetry of a swept cylinder (which represented the wing leading-edge) which was mounted on a wedge (which generated the "bow" shock wave). A numerical code was developed using integral techniques to calculate the flow in the shock layer upstream of the interaction region (i.e., near the wing root). Heat transfer rates were calculated for various free stream conditions. The present investigation was undertaken to examine the effects of crossflow on the resultant flow-field and to verify the flow model used in theoretical calculations.

Barnette, D. W.↗

NASA NTRS1978

Stress intensity factors in a cracked infinite elastic wedge loaded by a rigid punch

A plane elastic wedge-shaped solid was split through the application of a rigid punch. It was assumed that the coefficient of friction on the the contact area was constant, and the problem had a plane of symmetry with respect to loading and geometry, with the crack in the plane of symmetry. The problem was formulated in terms of a system of integral equations with the contact stress and the derivative of the crack surface displacement as the unknown functions. The solution was obtained for an internal crack and for an edge crack. The results include primarily the stress intensity factors at the crack tips, and the measure of the stress singularity at the wedge apex, and at the end points of the contact area.

Erdogan, F.↗

NASA NTRS1978

Experimental and analytical investigation of a nonaxisymmetric wedge nozzle at static conditions

An experimental investigation of a nonaxisymmetric wedge nozzle was conducted at static conditions. The resulting data, in the form of detailed pressure distributions and oil flow photographs, expand the current nonaxisymmetric nozzle data base. An analytical investigation has been conducted to evaluate a two-dimensional, inviscid, time-dependent theory as a nonaxisymmetric nozzle performance predictor. For the range of nozzle pressure ratios investigated, results indicate good agreement between theory and experiment in regions of predominately two-dimensional flow and limited agreement in regions of three-dimensional flow. For the wedge nozzle and related nozzle configurations, the two dimensional, inviscid theory may be applied as a limited performance predictor.

Carson, G. T., Jr.↗

NASA NTRS1979

Three-dimensional finite-element elastic analysis of a thermally cycled single-edge wedge geometry specimen

An elastic stress analysis was performed on a wedge specimen (prismatic bar with single-wedge cross section) subjected to thermal cycles in fluidized beds. Seven different combinations consisting of three alloys (NASA TAZ-8A, 316 stainless steel, and A-286) and four thermal cycling conditions were analyzed. The analyses were performed as a joint effort of two laboratories using different models and computer programs (NASTRAN and ISO3DQ). Stress, strain, and temperature results are presented.

Bizon, P. T.↗

NASA NTRS1979

Performance characteristics of a wedge nozzle installed on an F-18 propulsion wind tunnel model

The results of two-dimensional wedge non-axisymmetric nozzle (2D-AIN) tests to determine its performance relative to the baseline axisymmetric nozzle using an F-18 jet effects wind tunnel model are presented. Configurations and test conditions simulated forward thrust-minus drag, thrust vectoring/induced lift, and thrust reversing flight conditions from Mach .6 to 1.20 and attack angles up to 10 degrees. Results of the model test program indicate that non-axisymmetric nozzles can be installed on a twin engine fighter aircraft model with equivalent thrust minus drag performance as the baseline axisymmetric nozzles. Thrust vectoring capability of the non-axisymmetric nozzles provided significant jet-induced lift on the nozzle/aftbody and horizontal tail surfaces. Thrust reversing panels deployed from the 2D-AIN centerbody wedge were very effective for static and inflight operation

Petit, J. E.↗

NASA NTRS1981

Interlocking wedge joint is easily assembled

Wedge joint links structural members in manual, remote, or automated assemblies. Joint is simple enough to be assembled by undersea divers, workers in nuclear reactors, and other wearing gloves or bulky clothing. Combination of wedging angles on parts overcomes structural misalinements and forces assembly into true position as locking sleeve moves into place. Joint transmits tension, compression, bending moments and torsion and is inherently insensitive to thermal excursions, vibration, and machining tolerance buildup.

Long, M. J.↗

NASA NTRS1983

Wedge coupling of lasers into multimode fibers

Design and experimental data for obtuse-angled wedges used in coupled configurations of diode lasers and multimode fibers are presented. An analytic definition of the connection between the wedge angle and the fiber acceptance half-angle is developed, along with a formula for the minimum half-angle. An inequality is defined for determining the bevel angle of the output end of the fiber to eliminate end reflections. The fiber parameters are accounted for in the bevel. The formulations were tested in comparison with the performance of a coupled CDH laser system and good agreement was found in the output spectrum.

Ladany, I.↗

NASA NTRS1983

Hypersonic slender-wedge analysis with gradual change in angle of attack

The behavior of a narrow cross-section wedge wing moving at a high Mach number and subjected to an angle of attack changing exponentially with time is investigated. This type of wedge wing is commonly employed as a lifting surface in hypersonic vehicles. The time history of wall shear, heat transfer, displacement thickness, and viscous induced pressure are determined. Results show that for the same change in angle of attack, the flow attains the final steady state much faster when the change is exponential than when the change is made impulsively. In addition, the unsteady character of the flow is primarily confined to the initial stages of the change in the angle of attack.

Gupta, R. N.↗

NASA NTRS1986

Wedged Fibers Suppress Feedback of Laser Beam

When injected laser is coupled into optical fiber, emission instabilities arise because of optical feedback losses from fiber into laser. Coupling efficiencies as high as 80 percent, however, obtained by shaping end of multimode fiber into obtuse-angled wedge. Because slanted sides eliminate back reflection, such wedged fiber achieves high coupling efficiency.

Ladany, I.↗

NASA NTRS1988

Electromagnetic scattering by pyramidal and wedge absorber

Electromagnetic scattering from pyramidal and wedge absorbers used to line the walls of modern anechoic chambers is measured and compared with theoretically predicted values. The theoretical performance for various angles of incidence is studied. It is shown that a pyramidal absorber scatters electromagnetic energy more as a random rough surface does. The apparent reflection coefficient from an absorber wall illuminated by a plane wave can be much less than the normal absorber specifications quoted by the manufacturer. For angles near grazing incidence, pyramidal absorbers give a large backscattered field from the pyramid side-faces or edges. The wedge absorber was found to give small backscattered fields for near-grazing incidence. Based on this study, some new guidelines for the design of anechoic chambers are advocated because the specular scattering models used at present do not appear valid for pyramids that are large compared to the wavelength.

Dewitt, Brian T.↗

NASA NTRS1990

A multisatellite case study of the expansion of a substorm current wedge in the near-earth magnetotail

Results are presented on observations from four satellites (GOES 5, GOES 6, AMPTE CCE, and AMPTE IRM) and two ground stations (San Juan and Tucson) on a substorm that occurred on April 19, 1985 at about 0830 UT. The four spacecraft were arrayed in a configuration that made it possible to separate the effects arising from the longitudinal versus the radial expansion of the substorm current wedge and thus to examine its spatial evolution. The sequence of events that was observed suggests that, during this substorm, the disruption of the cross-tail current sheet, the formation of the substorm current wedge, and the expansion of the plasma sheet began in the near-earth region, and subsequently spread tailward as well as longitudinally.

Lopez, R. E.↗

NASA NTRS1990

Determination of refractive index of a simple negative, positive, or zero power lens using wedged plated interferometer

A nondestructive technique for measuring the refractive index of a negative lens using a wedged plate interferometer is described. The method can be also used for measuring the refractive index of convex or zero power lenses. Schematic diagrams are presented for the use of a wedged plate interferometer for measuring the refractive index of a concave lens and of a convex lens.

Shukla, R. P.↗

NASA NTRS1994

Flexible Wedge Seal For Ball Valve

Ball valve contains flexible sealing wedge. Wedge flexes around ball at locus of contact, creating effective seal with less force on ball than if hard valve seat were used. Less torque needed to close valve, and smaller actuator used.

Levert, Joseph A.↗

NASA NTRS1994

An automated optical wedge calibrator for Dobson ozone spectrophotometers

The Dobson ozone spectrophotometer measures the difference of intensity between selected wavelengths in the ultraviolet. The method uses an optical attenuator (the 'Wedge') in this measurement. The knowledge of the relationship of the wedge position to the attenuation is critical to the correct calculation of ozone from the measurement. The procedure to determine this relationship is time-consuming, and requires a highly skilled person to perform it correctly. The relationship has been found to change with time. For reliable ozone values, the procedure should be done on a Dobson instrument at regular intervals. Due to the skill and time necessary to perform this procedure, many instruments have gone as long as 15 years between procedures. This article describes an apparatus that performs the procedure under computer control, and is adaptable to the majority of existing Dobson instruments. Part of the apparatus is usable for normal operation of the Dobson instrument, and would allow computer collection of the data and real-time ozone measurements.

Evans, R. D.↗

NASA NTRS1994

Capillary surfaces in a wedge: Differing contact angles

The possible zero-gravity equilibrium configurations of capillary surfaces u(x, y) in cylindrical containers whose sections are (wedge) domains with corners are investigated mathematically, for the case in which the contact angles on the two sides of the wedge may differ. In such a situation the behavior can depart in significant qualitative ways from that for which the contact angles on the two sides are the same. Conditions are described under which such qualitative changes must occur. Numerically computed surfaces are depicted to indicate the behavior.

Concus, Paul↗

NASA NTRS1961

Exploratory Investigation of Transpiration Cooling of a 40 Degree Double Wedge Using Nitrogen and Helium as Coolants at Stagnation Temperatures from 1,295 Degrees Fahrenheit to 2,910 Degrees Fahrenheit

An investigation of transpiration cooling has been conducted in the preflight jet of the Langley Pilotless Aircraft Research Station at Wallops Island, Va. The model consisted of a double wedge of 40 deg included angle having a porous stainless-steel specimen inserted flush with the top surface of the wedge. The tests were conducted at a free-stream Mach number of 2.0 for stagnation temperatures ranging from 1,295 F to 2,910 F. Nitrogen and helium were used as coolants and tests were conducted for values ranging from approximately 0.03 to 0.30 percent of the local weight flow rate. The data for both the nitrogen and helium coolants indicated greater cooling effectiveness than that predicted by theory and were in good agreement with the results for an 8 deg cone tested at a stagnation temperature of 600 F. The results indicate that the helium coolant, for the same amount of heat-transfer reduction, requires only about one-fourth to one-fifth the coolant flow weight as the nitrogen coolant.

Rashis, Bernard↗

NASA NTRS2010

Computational Analysis of Arc-Jet Wedge Tests Including Ablation and Shape Change

Coupled fluid-material response analyses of arc-jet wedge ablation tests conducted in a NASA Ames arc-jet facility are considered. These tests were conducted using blunt wedge models placed in a free jet downstream of the 6-inch diameter conical nozzle in the Ames 60-MW Interaction Heating Facility. The fluid analysis includes computational Navier-Stokes simulations of the nonequilibrium flowfield in the facility nozzle and test box as well as the flowfield over the models. The material response analysis includes simulation of two-dimensional surface ablation and internal heat conduction, thermal decomposition, and pyrolysis gas flow. For ablating test articles undergoing shape change, the material response and fluid analyses are coupled in order to calculate the time dependent surface heating and pressure distributions that result from shape change. The ablating material used in these arc-jet tests was Phenolic Impregnated Carbon Ablator. Effects of the test article shape change on fluid and material response simulations are demonstrated, and computational predictions of surface recession, shape change, and in-depth temperatures are compared with the experimental measurements.

Goekcen, Tahir↗