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  • Other Sources  (984)
  • AERODYNAMICS  (684)
  • INSTRUMENTATION AND PHOTOGRAPHY  (300)
  • 1990-1994  (984)
  • 1925-1929
  • 1991  (984)
  • 1
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    Variable sensitivity moire interferometry (1991)
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    Publication Date: 2011-08-24
    Description: This paper demonstrates that optical microlithography can be used to produce a crossed grating which diffracts light into multiple orders sufficient to record moire interferograms with sensitivities ranging from 2.0 to 0.285 micron/fringe. The grating profile produced by the method is analyzed to establish the diffraction efficiency in each diffraction order, and generalized expressions are given for variable sensitivity moire interferometry. Experimental tests are conducted to verify analytical arguments. In one of these tests, two different diffraction order pairs are used simultaneously to verify that surface displacement can be measured at different sensitivities.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: 1991 SEM Spring Conference on Experimental Mechanics, Milwaukee, WI, June 10-13, 1991, Proceedings (A93-16601 04-39); p. 268-277.
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  • 2
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    Sapphire fiber interferometer for microdisplacement measurements at high temperatures (1991)
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    Publication Date: 2011-08-24
    Description: We report the use of a short-length, multimode sapphire rod as an extension to a Michelson configuration, but operated as a low-finesse Fabry-Perot cavity. We demonstrate the performance of such a device as an interferometric sensor, where the interference between the reflections from the sapphire-air interface and an air-metallic surface is observed for microdisplacement of the metallic surface which is placed close to the sapphire endface. We describe in detail the fabrication procedure and present results obtained from the detection of temperature changes, applied strain, and surface acoustic waves.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Fiber optic smart structures and skins IV; Proceedings of the Meeting, Boston, MA, Sept. 5, 6, 1991 (A93-21068 06-35); p. 117-124.
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  • 3
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    Multiresponse imaging system design for improved resolution (1991)
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    Publication Date: 2011-08-24
    Description: Multiresponse imaging is a process that acquires A images, each with a different optical response, and reassembles them into a single image with an improved resolution that can approach 1/sq rt A times the photodetector-array sampling lattice. Our goals are to optimize the performance of this process in terms of the resolution and fidelity of the restored image and to assess the amount of information required to do so. The theoretical approach is based on the extension of both image restoration and rate-distortion theories from their traditional realm of signal processing to image processing which includes image gathering and display.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: ; : Problems in the ae
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  • 4
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    The hypersonic double ellipse in rarefied flow (1991)
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    Publication Date: 2011-08-24
    Description: The problem of the hypersonic double ellipse in rarefied flow is treated by a particle method using the collision model first described by McDonald (1988). In the approach used here, the computational overhead is reduced by using simple cubic cells. The problem of the definition of complex geometries is addressed by developing an algorithm to define the relation of a body surface to the network of cells.
    Keywords: AERODYNAMICS
    Type: In: Hypersonic flows for reentry problems. Vol. 2 (A93-42576 17-02); p. 912-923.
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  • 5
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    Application of program LAURA to thermochemical nonequilibrium flow through a nozzle (1991)
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    Publication Date: 2011-08-24
    Description: Program LAURA (Langley Aerothermodynamic Upwind Relaxation Algorithm) is an upwind-biased, point-implicit relaxation algorithm for obtaining the numerical solution to the governing equations for 3D viscous hypersonic flows in chemical and thermal nonequilibrium. The algorithm is derived using a finite-volume formulation in which the inviscid components of flux across cell walls are described with a modified Roe's averaging and with second-order corrections based on Yee's Symmetric Total Variation Diminishing scheme. The code has been applied to Problem 8.2 of this workshop for the case of thermochemical nonequilibrium flow through a nozzle. Chemical reaction rates are defined with the model of Park (1987). Thermal nonequilibrium is modeled using a two-temperature approximation in which the vibrational energies of all molecules are assumed to be in equilibrium at a single temperature which is generally different from the translational-rotational temperature. Two grids were used to define the flow for the original problem, with a stagnation temperature of 6500 K. A third case with a stagnation temperature of 10,000 K is also presented. The solution domain includes the converging nozzle, subsonic flow domain in which the gas is substantially in thermochemical equilibrium and the diverging nozzle, hypersonic flow domain in which the gas is substantially in thermochemical nonequilibrium.
    Keywords: AERODYNAMICS
    Type: In: Hypersonic flows for reentry problems. Vol. 2 (A93-42576 17-02); p. 1145-1158.
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  • 6
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    Hypersonic cone flow predictions using an implicit upwind space-marching code (1991)
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    Publication Date: 2011-08-24
    Description: Solutions have been computed and results are presented for Problem 1, the case of Mach 9 transitional flow past a 7 deg half-angle cone at zero incidence. The solutions were computed using a code developed for the integration of the parabolized Navier-Stokes equations. The algorithm employed in the code is based on a Roe-type flux-difference-splitting scheme applied following a finite-volume approach. The basic algorithm has been modified to make it implicit and second-order accurate in the crossflow directions. Results are presented in terms of surface pressure and heat transfer as well as boundary layer profiles of pitot pressure, Mach number, and tangential velocity. The case was recalculated several times in an effort to determine sensitivities to such parameters as grid density, wall temperature, turbulence model parameters, as well as freestream expansion. Comparisons with the experimental data are presented and discussed.
    Keywords: AERODYNAMICS
    Type: In: Hypersonic flows for reentry problems. Vol. 2 (A93-42576 17-02); p. 75-91.
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  • 7
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    Thin film diamond microstructure applications (1991)
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    Publication Date: 2011-08-24
    Description: Selective deposition and abrasion, as well as etching in atomic oxygen or reduced-pressure air, have been used to prepare patterned polycrystalline diamond films which, on further processing by anisotropic Si etching, yield the microstructures of such devices as flow sensors and accelerometers. Both types of sensor have been experimentally tested in the respective functions of hot-wire anemometer and both single- and double-hinged accelerometer.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Applications of diamond films and related materials; Proceedings of the 1st International Conference, Auburn, AL, Aug. 17-22, 1991 (A93-40551 16-76); p. 311-318.
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  • 8
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    Correlation of airloads on a two-bladed helicopter rotor (1991)
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    Publication Date: 2011-08-24
    Description: Airloads measured on a two-bladed helicopter rotor in flight, from the Tip Aerodynamic and Acoustic Test, are compared with calculations from a comprehensive helicopter analysis (CAMRAD/JA), and the pressures compared with calculations from a full-potential rotor code (FPR). The flight test results cover an advance ratio range from 0.19 to 0.38. The lowest speed case is characterized by the presence of significant blade-vortex interactions. Good correlation of peak-to-peak vortex-induced loads and the corresponding pressures is obtained. The results of the correlation for this two-bladed rotor are substantially similar to the results for three- and four-bladed rotors, concerning the tip vortex core size for best correlation, calculation of the peak-to-peak loads on the retreating side, and calculation of vortex-induced loads on inboard radial stations.
    Keywords: AERODYNAMICS
    Type: In: AHS and Royal Aeronautical Society, Technical Specialists' Meeting on Rotorcraft Acoustics(Fluid Dynamics, Philadelphia, PA, Oct. 15-17, 1991, Proceedings (A93-29401 10-71); 38 p.
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  • 9
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    The development of a CFD potential method for the analysis of tilt-rotors (1991)
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    Publication Date: 2011-08-24
    Description: A new CFD potential code, FPX (eXtended Full-Potential), has been developed for application to both helicopters and tilt-rotors. The code solves the unsteady, three-dimensional full potential equation and is an extension of the rotor code, FPR. Both entropy and viscosity corrections are included to enhance the physical modeling capabilities. A number of efficiency related modifications have yielded a factor of two speed-up in the code. An axial flow capability has been added to treat tilt-rotor in forward flight (cruise mode). In order to employ streamwise periodicity and accurately solve for the propagation of acoustic signals in the tip region, an H-H topology has been added to the basic O-H grid system. Computations are performed for the XV-15 Standard and ATB blades at high-speed conditions. Comparisons are made for the blade aerodynamics and the induced fuselage cabin pressure for a range of Mach numbers. Grid generation, wake treatment, and far-field wall treatment are identified as problem areas with recommendations for future research.
    Keywords: AERODYNAMICS
    Type: In: AHS and Royal Aeronautical Society, Technical Specialists' Meeting on Rotorcraft Acoustics(Fluid Dynamics, Philadelphia, PA, Oct. 15-17, 1991, Proceedings (A93-29401 10-71); 15 p.
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  • 10
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    Recent developments in rotor wake modeling for helicopter noise prediction (1991)
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    Publication Date: 2011-08-24
    Description: A preliminary test/theory correlation evaluation is conducted for wake measurement test results obtained by LDV for a B360 helicopter rotor, at conditions critical to the understanding of wake-rollup and blade-vortex interaction phenomena. The LDV data were complemented by acoustic, blade pressure, rotor performance, and blade/control load measurements.
    Keywords: AERODYNAMICS
    Type: In: AHS and Royal Aeronautical Society, Technical Specialists' Meeting on Rotorcraft Acoustics(Fluid Dynamics, Philadelphia, PA, Oct. 15-17, 1991, Proceedings (A93-29401 10-71); 16 p.
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  • 11
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    Grid-refinement study of hypersonic laminar flow over a 2-D ramp (1991)
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    Publication Date: 2011-08-24
    Description: Computations were made for those test cases of Problem 3 which were designated as laminar flows, viz., test cases 3.1, 3.2, 3.4, and 3.5. These test cases corresponded to flows over a flat plate and a compression ramp at high Mach number and at high Reynolds number. The computations over the compression ramps indicate a substantial streamwise extent of separation. Based on previous experience with separated laminar flows at high Mach numbers which indicated a substantial effect with spatial grid refinement, a series of computations with different grid sizes were performed. Also, for the flat plate, comparisons of the results for two different algorithms were made.
    Keywords: AERODYNAMICS
    Type: In: Hypersonic flows for reentry problems. Vol. 2 (A93-42576 17-02); p. 244-254.
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  • 12
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    Computational fluid dynamics for hypersonic airbreathing aircraft (1991)
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    Publication Date: 2011-08-24
    Description: A development status evaluation is presented for CFD methods applicable to fuselage-integrated scramjet powerplant incorporating hypersonic vehicles; these methods are critically important due to the unavailability of experimental facilities for such elevated Mach number/high-enthalphy conditions. Advancements are required in algorithm robustness and speed, geometric flexibility, and the inclusion of more complete flow physics. The most serious deficiencies lie in turbulence modeling, the lack of complete transition-prediction methods, and combustion modeling.
    Keywords: AERODYNAMICS
    Type: In: Hypersonic flows for reentry problems. Vol. 1 (A93-42576 17-02); p. 55-71.
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  • 13
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    CFD for hypersonic propulsion (1991)
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    Publication Date: 2011-08-24
    Description: An overview is given of research activity on the application of computational fluid dynamics (CDF) for hypersonic propulsion systems. After the initial consideration of the highly integrated nature of air-breathing hypersonic engines and airframe, attention is directed toward computations carried out for the components of the engine. A generic inlet configuration is considered in order to demonstrate the highly three dimensional viscous flow behavior occurring within rectangular inlets. Reacting flow computations for simple jet injection as well as for more complex combustion chambers are then discussed in order to show the capability of viscous finite rate chemical reaction computer simulations. Finally, the nozzle flow fields are demonstrated, showing the existence of complex shear layers and shock structure in the exhaust plume. The general issues associated with code validation as well as the specific issue associated with the use of CFD for design are discussed. A prognosis for the success of CFD in the design of future propulsion systems is offered.
    Keywords: AERODYNAMICS
    Type: In: Hypersonic flows for reentry problems. Vol. 1 (A93-42576 17-02); p. 170-186.
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  • 14
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    Aircraft laser infrared absorption spectrometer (ALIAS) for polar ozone studies (1991)
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    Publication Date: 2011-08-24
    Description: The ALIAS instrument is a very high resolution (0.0003/cm) scanning, tunable diode laser spectrometer designed to make direct, simultaneous measurements of NO2, HNO3, HCl, CH4, and either O3 or N2O (including vertical profiles of CH4 and N2O) in the polar stratosphere at sub-part-per-billion level sensitivities over integration times from 3 to 30 s. Unique features include a sample inlet/throttle system designed to achieve near-isokinetic sampling, in PSC events, an in-flight wavelength reference cell rack, mechanical fringe-spoilers, a four-laser/four-detector dewar with 24-hr hold-time operating at a fixed temperature without electrical regulation, and in-flight fast correlation routines for spectral drift compensation prior to spectral addition. Instrument design and test flight results are discussed in the light of ALIAS's role in the Winter 1991 Arctic aircraft stratospheric ozone campaigns out of Fairbanks, Alaska, and Bangor, Maine.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Infrared technology XVII; Proceedings of the Meeting, San Diego, CA, July 22-26, 1991 (A93-38376 15-35); p. 187-194.
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  • 15
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    High throughput narrowband 83.4 nm self-filtering camera (1991)
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    Publication Date: 2011-08-24
    Description: Photometric imaging of ionospheric/magnetospheric O II emission at 83.4 nm is a primary objective for mapping the distribution of O(+) ions. However, instrumental sensitivity has been a major barrier to realizing this goal. We report an instrumental design employing a low focal ratio three-mirror camera where the reflecting surfaces act as both narrowband reflection filters at 83.4 nm and as a high quality imaging system. The design includes coatings with reflectances that are relatively insensitive to the angle of incidence of light. The peak reflectance per mirror is more than 60 percent at 83.4 nm with the average reflectance for out-of-band wavelengths of less than 5 percent. The net reflective transmission for the three mirrors is greater than 20 percent with 6.8 nm bandwidth and 0.01 percent maximum transmittance for out-of-band wavelengths. The transmittance at 30.4 nm is 0.03 percent at 58.4 nm 0.05 percent, and at 121.6 nm 0.004 percent. When used with an open microchannel plate detector, contamination by H Ly-alpha is essentially eliminated. With this spectral purity and effective elimination of major contributors to background contamination noise, a signal-to-noise ratio (excluding detector noise) of 10 is achievable for a 0.01 R signal in 8.8 seconds for the full 6 deg field-of-view.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: EUV, X-ray, and gamma-ray instrumentation for astronomy II; Proceedings of the Meeting, San Diego, CA, July 24-26, 1991 (A93-34376 13-35); p. 234-244.
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  • 16
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    Characteristics of a high pressure gas proportional counter filled with xenon (1991)
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    Publication Date: 2011-08-24
    Description: The characteristics of a conventional cylindrical geometry proportional counter filled with high pressure xenon gas up to 10 atm. were fundamentally investigated for use as a detector in hard X-ray astronomy. With a 2 percent methane gas mixture the energy resolutions at 10 atm. were 9.8 percent and 7.3 percent for 22 keV and 60 keV X-rays, respectively. From calculations of the Townsend ionization coefficient, it is shown that proportional counters at high pressure operate at weaker reduced electric field than low pressure counters. The characteristics of a parallel grid proportional counter at low pressure showed similar pressure dependence. It is suggested that this is the fundamental reason for the degradation of resolution observed with increasing pressure.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: EUV, X-ray, and gamma-ray instrumentation for astronomy II; Proceedings of the Meeting, San Diego, CA, July 24-26, 1991 (A93-34376 13-35); p. 20-27.
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  • 17
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    Error analysis of combined stereo/optical-flow passive ranging (1991)
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    Publication Date: 2011-08-24
    Description: The motion of an imaging sensor causes each imaged point of the scene to correspondingly describe a time trajectory on the image plane. The trajectories of all imaged points are reminiscent of a flow (e.g., of liquid) which is the source of the term 'optical flow'. Optical-flow ranging is a method by which the stream of two-dimensional images obtained from a forward-looking forward-moving passive sensor is used to compute depth (or range) to points in the field of view. Another well-known ranging method consists of triangulation based on stereo images obtained from at least two stationary sensors. In this paper we analyze the potential accuracies of a combined optical flow and stereo passive-ranging system in the context of helicopter nap-of-the-earth obstacle avoidance. The Cramer-Rao lower bound is developed for the combined system under the assumption of an unknown angular bias error common to both cameras of a stereo pair. It is shown that the depth accuracy degradations caused by a bias error is negligible for a combined optical-flow and stereo system as compared to a monocular optical-flow system.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Surveillance technologies; Proceedings of the Meeting, Orlando, FL, Apr. 2-5, 1991 (A93-27712 09-35); p. 259-267.
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  • 18
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    High Tc bolometer developments for planetary missions (1991)
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    Publication Date: 2011-08-24
    Description: A simple polishing technique was developed for thinning the LaAlO3 substrates for high-quality Tc bolometer films, and thus reducing their heat capacity. A 150-ms bolometer was made on a LaAlO3 substrate with a 5-Hz D* value of 1.5 x 10 exp 8. It is shown that passive temperature stabilization is adequate for operation at the transition. There remained excess noise at the transition, but this noise appears to be of nonbolometric origin.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Superconductivity applications for infrared and microwave devices II; Proceedings of the Meeting, Orlando, FL, Apr. 4, 5, 1991 (A93-27243 09-33); p. 166-173.
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  • 19
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    Passive range sensor refinement using texture and segmentation (1991)
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    Publication Date: 2011-08-24
    Description: Electrooptical sensors provide a covert way of computing range during helicopter flight. The optical flow-based computation of range provides range information only in certain distinguishable parts of the image. The regions where range information is available can be increased by performing texture analysis and object segmentation in the image. This paper reviews some of the literature on texture segmentation methods with a view towards applying them to images containing both man-made and natural objects at varying ranges. Two algorithmic approaches are given and their application to a real image is demonstrated. Results indicate that it will be necessary to combine several different texture measures and methods in a hierarchical way in order to achieve an object segmentation which is useful in enhancing range information.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Sensors and sensor systems for guidance and navigation; Proceedings of the Meeting, Orlando, FL, Apr. 2, 3, 1991 (A93-27043 09-19); p. 178-189.
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  • 20
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    Micro-displacement fiber sensor using two-frequency interferometry (1991)
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    Publication Date: 2011-08-24
    Description: A He-Ne Zeeman laser has been utilized as a two-frequency light source in a Michelson-type micro-displacement fiber sensor. A polarization maintaining fiber has been installed in the sensing arm, which facilitates flexibility and allows the sensing region to be remotely located. This fiber sensing arm is arranged to replace a quarterwave plate component. The fiber sensor system has a resolution of half a micrometer.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Fiber optic and laser sensors IX; Proceedings of the Meeting, Boston, MA, Sept. 3-5, 1991 (A93-53103 23-35); p. 146-151.
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  • 21
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    Fiber-optic thermometer using Fourier transform spectroscopy (1991)
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    Publication Date: 2011-08-24
    Description: An integrated-optic Mach-Zender interferometer is used as a Fourier transform spectrometer to analyze the input and output spectra of a temperature-sensing thin-film etalon. This configuration provides a high degree of immunity to the effects of changes in the source spectrum, and it readily permits the interrogation of a number of different sensors using a single spectrometer. In addition, this system has a potentially low cost because it uses optical communications hardware that may in the future be manufactured in large quantities.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Fiber optic and laser sensors IX; Proceedings of the Meeting, Boston, MA, Sept. 3-5, 1991 (A93-53103 23-35); p. 64-71.
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  • 22
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    Acoustic composition sensor for cryogenic gas mixtures (1991)
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    Publication Date: 2011-08-24
    Description: An acoustic sensor useful for the determination of the composition of a gaseous binary mixture in cryogenic liquid spills has been characterized. One version of the instrument traps a known mixture of helium and nitrogen at ambient temperature in a tube which is interrogated by sonic pulses to determine the speed of sound and hence the composition. Experimental data shows that this sensor is quite accurate. The second version uses two unconfined microphones which sense sound pulses. Experimental data acquired during mixing when liquid nitrogen is poured into a vessel of gaseous helium is presented. Data during transient cooling of the tubular sensor containing nitrogen when the sensor is dipped into liquid nitrogen and during transient warm-up when the sensor is withdrawn are also presented. This sensor is being developed for use in the mixing of liquid cryogens with gas evolution in the simulation of liquid hydrogen/liquid oxygen explosion hazards.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Advances in cryogenic engineering. Vol. 37B - Proceedings of the 1991 Cryogenic Engineering Conference, Univ. of Alabama, Huntsville, June 11-14, 1991 (A93-48578 20-37); p. 1453-1460.
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  • 23
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    Current instrument status of the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) (1991)
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    Publication Date: 2011-08-24
    Description: An upgraded version of AVIRIS, an airborne imaging spectrometer based on a whiskbroom-type scanner coupled via optical fibers to four dispersive spectrometers, that has been in operation since 1987 is described. Emphasis is placed on specific AVIRIS subsystems including foreoptics, fiber optics, and an in-flight reference source; spectrometers and detector dewars; a scan drive mechanism; a signal chain; digital electronics; a tape recorder; calibration systems; and ground support requirements.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Infrared technology XVII; Proceedings of the Meeting, San Diego, CA, July 22-26, 1991 (A93-38376 15-35); p. 164-175.
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  • 24
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    A fiber-coupled heterodyne interferometric displacement sensor (1991)
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    Publication Date: 2011-08-24
    Description: Space-based interferometers and large segmented reflectors will require precision metrology with nanometer accuracy for active control systems. This paper summarizes an experimental study of an optical heterodyne interferometer with resolution of about 3 nm. Optical signals are carried to and from the interferometer by optical fibers to avoid thermally loading the reflector panels. Heterodyne detection provides far greater precision than does traditional interferometry.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Active and adaptive optical systems; Proceedings of the Meeting, San Diego, CA, July 22-24, 1991 (A93-39451 15-74); p. 523-533.
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  • 25
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    Analysis of upper and lower bounds of the frame noise in linear detector arrays (1991)
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    Publication Date: 2011-08-24
    Description: This paper estimates the upper and lower bounds of the frame noise of a linear detector array that uses a one-dimensional scan pattern. Using chi-square distribution, it is analytically shown why it is necessary to use the average of the variances and not the average of the standard deviations to estimate these bounds. Also, a criteria for determining whether any excessively noisy lines exist among the detectors is derived from these bounds. Using a Gaussian standard random variable generator, these bounds are demonstrated to be accurate within the specified confidence interval. A silicon detector array is then used for actual dark current measurements. The criterion developed for determination of noisy detectors is checked on the experimentally obtained data.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Infrared sensors: Detectors, electronics, and signal processing; Proceedings of the Meeting, San Diego, CA, July 24-26, 1991 (A93-33153 12-35); p. 152-162.
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  • 26
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    Far-IR Fabry-Perot spectrometer for OH measurements (1991)
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    Publication Date: 2011-08-24
    Description: The Far Infrared Limb Observing Spectrometer (FILOS) is an instrument designed to measure chemical species in the upper atmosphere using limb emission in the far infrared region of the spectrum. FILOS uses three Fabry-Perot etalons in series to obtain a resolution of 0.0017/cm near 101/cm (99 microns). The instrumental concept and atmospheric measurements are discussed.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Remote sensing of atmospheric chemistry; Proceedings of the Meeting, Orlando, FL, Apr. 1-3, 1991 (A93-31376 11-35); p. 308-313.
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  • 27
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    Measurement of atmospheric composition by the ATMOS instrument from Table Mountain Observatory (1991)
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    Publication Date: 2011-08-24
    Description: Following its first flight on board the Space Shuttle 'Challenger' as part of the Spacelab 3 payload, the Atmospheric Trace Molecule Spectroscopy (ATMOS) instrument has been operated at the Jet Propulsion Laboratory's Table Mountain Observatory (TMO; 34.4 deg N, 117.7 deg W, 2.23 km altitude) in the San Gabriel Mountains of Southern California. With the delay in the resumption of regular Shuttle flights, ATMOS has acquired a large number of high-quality, high-resolution infrared solar absorption spectra, spanning a period between late-1985 and mid-1990. These spectra are being analyzed to derive the column abundances of several atmospheric species including O3, HCl, HF, and HNO3. Although limited in temporal coverage, the preliminary results for these gases are discussed here in the context of the requirement and contribution to be made by similar instruments in detecting long term changes in stratospheric composition.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Remote sensing of atmospheric chemistry; Proceedings of the Meeting, Orlando, FL, Apr. 1-3, 1991 (A93-31376 11-35); p. 335-346.
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    Detection of stratospheric ozone trends by ground-based microwave observations (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We present an assessment of the trend detection capabilities of ground-based microwave measurements of ozone, focusing on the 20-60 km region. Uncertainty due to variable forward model and calibration errors is 3-5 percent; due to temperature profile errors, 1-2 percent; and due to spectral measurement errors, 1-3 percent. The measurement resolution is 8-10 km below 40 km, and increases to 17 km at 60 km. The net error for trend detection is 4-6 percent. Comparison with other measurements suggests interannual variations can be measured to 3-5 percent. We conclude a trend of 0.5 percent per year would be detected in about 10 years.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Remote sensing of atmospheric chemistry; Proceedings of the Meeting, Orlando, FL, Apr. 1-3, 1991 (A93-31376 11-35); p. 218-230.
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    Ground-based lidar for long-term and network measurements of ozone (1991)
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    Publication Date: 2011-08-24
    Description: Attention is given to a ground-based differential absorption lidar system developed and operated at the JPL Table Mountain Facility for measurements of stratospheric ozone concentration profiles from approximately 15 to 20 km altitude. The seasonal variations observed between February 1988 and late 1990 are presented as a function of altitude. For the summer 1989 Stratospheric Ozone Intercomparison Campaign, the lidar measurements were found to agree with the average of the results obtained from seven different instruments over a 14-d period to within 5 percent over the altitude range 18 to 49 km. The status of this instrument is discussed, with emphasis on areas of improvement over the present system.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Remote sensing of atmospheric chemistry; Proceedings of the Meeting, Orlando, FL, Apr. 1-3, 1991 (A93-31376 11-35); p. 175-181.
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    Computational methods for shock waves in three-dimensional supersonic flow (1991)
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    Publication Date: 2011-08-24
    Description: A central artificial-viscosity and an upwind-biased difference method are contrived to solve the Euler equations for flowfields over typical spacecrafts. The spatial discretization is based on either nodal or cell-vertex formulation in the domain extending from free stream to the end of the vehicle. The outer boundary is treated as a bow shock in the first method but is placed in the free stream in the second, which captures both bow and internal shocks using an approximate Riemann solver based on high-order extrapolation to the cell face. These methods were tested for the Shuttle and Hermes orbiters at wind-tunnel conditions and angles of attack ranging from 0 to 60 deg. The artificial-viscosity method incorporated with a shock-fitting procedure shows smeared crossflow and wing-shock positions and required 15 percent more CPU per node than the upwind method. Greater flexibility and robustness is demonstrated by the latter on a fixed grid for all cases considered.
    Keywords: AERODYNAMICS
    Type: Computer Methods in Applied Mechanics and Engineering (ISSN 0045-7825); 87; 2-3,
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    Characterization of the Earth Radiation Budget Experiment radiometers (1991)
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    Publication Date: 2011-08-24
    Description: The Earth Radiation Budget Experiment (ERBE) scanning radiometers were used to measure the earth's radiation fields during the period November 1984 through February 1990. The ERBE radiometric packages were placed into orbit aboard the Earth Radiation Budget Satellite (ERBS) and the NOAA-9 and NOAA-10 spacecraft platforms. In each radiometric package, thermistor bolometers were used as detection elements for the broadband total (0,2 - 50,0 microns), shortwave (0,2 - 5,0 microns), and longwave (5,0 - 50,0 microns) spectral regions. Flight calibration facilities were built into each of the spacecraft radiometric packages. The flight facilities consisted of black bodies, tungsten lamps, and silicon photodiodes. The black bodies and tungsten lamps were found to be reliable at precision levels approaching 0,5 percent over a five-year period. The photodiodes were found to degrade more than 2 percent during the first year in orbit. In this paper, the flight calibration systems for the ERBE scanning radiometers are described along with the resultant measurements.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Metrologia (ISSN 0026-1394); 28; 183-187
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    Laser velocimetry measurements in non-isothermal CVD systems (1991)
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    Publication Date: 2011-08-24
    Description: Researchers at the NASA Langley Research Center are applying laser velocimetry (LV) techniques to characterize the fluid dynamics of non-isothermal flows inside fused silica chambers designed for chemical vapor deposition (CVD). Experimental issues involved in the application of LV techniques to this task include thermophoretic effects on the LV seed particles, seeding the hazardous gases, index of refraction gradients in the flow field and surrounding media, optical access, relatively low flow velocities, and analysis and presentation of sparse data. An overview of the practical difficulties these issues represent to the use of laser velocimetry instrumentation for CVD applications is given. A fundamental limitation on the application of LV techniques in non-isothermal systems is addressed which involves a measurement bias due to the presence of thermal gradients. This bias results from thermophoretic effects which cause seed particle trajectories to deviate from gas streamlines. Data from a research CVD reactor are presented which indicate that current models for the interaction of forces such as Stokes drag, inertia, gravity, and thermophoresis are not adequate to predict thermophoretic effects on particle-based velocimetry measurements in arbitrary flow configurations.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Laser anemometry - Advances and applications 1991; Proceedings of the 4th International Conference, Cleveland, OH, Aug. 5-9, 1991. Vol. 2 (A93-23776 08-35); p. 483-489.
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    High-speed laser anemometry based on spectrally resolved Rayleigh scattering (1991)
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    Publication Date: 2011-08-24
    Description: Laser anemometry in unseeded flows based on the measurement of the spectrum of Rayleigh scattered laser light is reviewed. The use of molecular scattering avoids the well-known problems (particle lag, biasing effects, seed generation, seed injection) of seeded flows. The fundamental limits on velocity measurement accuracy are determined using maximum likelihood methods. Measurement of the Rayleigh spectrum with scanning Fabry-Perot interferometers is analyzed and accuracy limits are established for both single pass and multi-pass configurations. Multi-pass configurations have much higher selectivity and are needed for measurements where there is a large amount of excess noise caused by stray laser light. It is shown that Rayleigh scattering is particularly useful for supersonic and hypersonic flows. The results of the analysis are compared with measurements obtained with a Rayleigh scattering diagnostic developed for study of the exhaust plume of a small hydrogen-oxygen rocket, where the velocities are in the range 1000 to 5000 m/sec.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Laser anemometry - Advances and applications 1991; Proceedings of the 4th International Conference, Cleveland, OH, Aug. 5-9, 1991. Vol. 2 (A93-23776 08-35); p. 465-471.
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    Young's fringe particle image velocimetry in the presence of random particle motions (1991)
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    Publication Date: 2011-08-24
    Description: In the Young's fringe approach to particle image velocimetry, random particle motions cause loss of fringe visibility by decorrelating the coherent interexposure particle separations responsible for fringe formation. Since the visibility reduction is determined by the random motion through a Fourier transform relation analogous to the Van Cittert Zernike Theorem, it has been proposed that the random motion can be characterized statistically by analyzing fringe visibility distributions in the transform plane. This paper assesses the accuracy of such measurements. In particular, the effects of finite particle population and of correlated random motion are evaluated. The theory applies to diffusive motion, turbulence, and to random motion caused by mean velocity inhomogeneities.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Laser anemometry - Advances and applications 1991; Proceedings of the 4th International Conference, Cleveland, OH, Aug. 5-9, 1991. Vol. 1 (A93-23776 08-35); p. 337-340.
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    Particle displacement tracking applied to air flows (1991)
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    Publication Date: 2011-08-24
    Description: Electronic Particle Image Velocimetric (PIV) techniques offer many advantages over conventional photographic PIV methods such as fast turn around times and simplified data reduction. A new all electronic PIV technique was developed which can measure high speed gas velocities. The Particle Displacement Tracking (PDT) technique employs a single CW laser, small seed particles (1 micron), and a single intensified, gated CCD array frame camera to provide a simple and fast method of obtaining two-dimensional velocity vector maps with unambiguous direction determination. Use of a single CCD camera eliminates registration difficulties encountered when multiple cameras are used to obtain velocity magnitude and direction information. An 80386 PC equipped with a large memory buffer frame-grabber board provides all of the data acquisition and data reduction operations. No array processors of other numerical processing hardware are required. Full video resolution (640 x 480 pixel) is maintained in the acquired images, providing high resolution video frames of the recorded particle images. The time between data acquisition to display of the velocity vector map is less than 40 sec. The new electronic PDT technique is demonstrated on an air nozzle flow with velocities less than 150 m/s.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Laser anemometry - Advances and applications 1991; Proceedings of the 4th International Conference, Cleveland, OH, Aug. 5-9, 1991. Vol. 1 (A93-23776 08-35); p. 327-335.
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    Doppler global velocimetry - A new way to look at velocity (1991)
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    Publication Date: 2011-08-24
    Description: A new laser velocimetry technique, Doppler global velocimetry, is described. This technique is capable of simultaneously measuring in real time the three components of velocity of an entire particle field illuminated by a laser light sheet. A prototype one-component velocimeter is described along with the signal processing electronics. The system was tested by measuring the velocity field from a rotating wheel and a small subsonic jet flow in the laboratory. The first wind tunnel test measured the vortical velocity field above a delta wing. The results are presented and compared with fringe-type laser velocimeter and five-hole probe data.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Laser anemometry - Advances and applications 1991; Proceedings of the 4th International Conference, Cleveland, OH, Aug. 5-9, 1991. Vol. 1 (A93-23776 08-35); p. 289-296.
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    A histogram-based technique for rapid vector extraction from PIV photographs (1991)
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    Publication Date: 2011-08-24
    Description: A new analysis technique, performed totally in the image plane, is proposed which rapidly extracts all available vectors from individual interrogation regions on PIV photographs. The technique avoids the need for using Fourier transforms with the associated computational burden. The data acquisition and analysis procedure is described, and results of a preliminary simulation study to evaluate the accuracy of the technique are presented. Recently obtained PIV photographs are analyzed.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Laser anemometry - Advances and applications 1991; Proceedings of the 4th International Conference, Cleveland, OH, Aug. 5-9, 1991. Vol. 1 (A93-23776 08-35); p. 279-288.
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    Particle image velocimetry for the Surface Tension Driven Convection Experiment using a particle displacement tracking technique (1991)
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    Publication Date: 2011-08-24
    Description: The Surface Tension Driven Convection Experiment (STDCE) is a Space Transportation System flight experiment to study both transient and steady thermocapillary fluid flows aboard the USML-1 Spacelab mission planned for 1992. One of the components of data collected during the experiment is a video record of the flow field. This qualitative data is then quantified using an all electronic, two-dimensional particle image velocimetry technique called particle displacement tracking (PDT) which uses a simple space domain particle tracking algorithm. The PDT system is successful in producing velocity vector fields from the raw video data. Application of the PDT technique to a sample data set yielded 1606 vectors in 30 seconds of processing time. A bottom viewing optical arrangement is used to image the illuminated plane, which causes keystone distortion in the final recorded image. A coordinate transformation was incorporated into the system software to correct this viewing angle distortion. PDT processing produced 1.8 percent false identifications, due to random particle locations. A highly successful routine for removing the false identifications was also incorporated, reducing the number of false identifications to 0.2 percent.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Laser anemometry - Advances and applications 1991; Proceedings of the 4th International Conference, Cleveland, OH, Aug. 5-9, 1991. Vol. 1 (A93-23776 08-35); p. 315-325.
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    Fiber optic laser Doppler anemometry in swirling jets (1991)
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    Publication Date: 2011-08-24
    Description: Time-averaged and fluctuating quantities are measured in a free turbulent swirling jet. Data from a two-component laser Doppler anemometry (LDA) are compared to the measurements via hot-wire and 5-hole pitot probes. To acquire the proper seeding density near the axis of a swirling jet for LDA measurements proved difficult. This is due to an imbalance of the centrifugal force and radial pressure gradient, which throws the seeding material off the axis. Despite this problem, close agreement between various measurement techniques is obtained.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Laser anemometry - Advances and applications 1991; Proceedings of the 4th International Conference, Cleveland, OH, Aug. 5-9, 1991. Vol. 1 (A93-23776 08-35); p. 77-82.
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    A technique for improving the calibration of large-area sphere sources (1991)
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    Publication Date: 2011-08-24
    Description: A new technique for improving the accuracy of radiance calibrations for large-area integrating-sphere sources has been investigated. Such sources are used to calibrate numerous aircraft and spacecraft remote sensing instruments. Recent measurements performed at NIST and NASA Goddard Space Flight Center have demonstrated that the uncertainty of sphere-source radiance measurements can be improved from the present 5 to 10 percent level to a 1 to 2 percent level. Silicon detectors with bandpass filters mounted in front of them and calibrated for absolute spectral responsivity can be used to confirm and to monitor the absolute radiance of a sphere source.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Calibration of passive remote observing optical and microwave instrumentation; Proceedings of the Meeting, Orlando, FL, Apr. 3-5, 1991 (A93-23575 07-19); p. 224-230.
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    Practical approaches for application of hi-temperature strain gages on high temperature composites (1991)
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    Publication Date: 2011-08-24
    Description: Four major areas of interest with respect to utilizing strain gages on carbon/carbon (with SiC surfaces) and titanium matrix composites are addressed. Strain gage and adhesive combinations on carbon/carbon (C/C) at temperatures from minus 190 C to 540 C, half-bridge gaging for reducing apparent strain on C/C using Poisson's ratio and bending configurations, review of the 'field installation' techniques developed for gaging a C/C hypersonic generic elevon, and results of initial strain gaging efforts on titanium matrix composites are discussed. Current research in developing techniques for increasing the maximum temperature for strain gages on carbon/carbon are reviewed.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: 1991 SEM Spring Conference on Experimental Mechanics, Milwaukee, WI, June 10-13, 1991, Proceedings (A93-16601 04-39); p. 180-189.
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    High-Reynolds-number test requirements in low-speed aerodynamics (1991)
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    Publication Date: 2011-08-24
    Description: Research requirements to an ultra-high-Reynolds-number liquid helium facility are reviewed. Aerodynamic research areas under consideration include wave vortex hazard reduction, vortex control and diagnostics for maneuvering fighter aircraft, and performance of high-lift devices.
    Keywords: AERODYNAMICS
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    Flow visualization (1991)
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    Publication Date: 2011-08-24
    Description: Flow visualization techniques are reviewed, with particular attention given to those applicable to liquid helium flows. Three techniques capable of obtaining qualitative and quantitative measurements of complex 3D flow fields are discussed including focusing schlieren, particle image volocimetry, and holocinematography (HCV). It is concluded that the HCV appears to be uniquely capable of obtaining full time-varying, 3D velocity field data, but is limited to the low speeds typical of liquid helium facilities.
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    Engineering calculations of three-dimensional inviscid hypersonic flowfields (1991)
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    Publication Date: 2011-08-24
    Keywords: AERODYNAMICS
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 28; 628-635
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    The inflatable sphere - A technique for the accurate measurement of middle atmosphere temperatures (1991)
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    Publication Date: 2011-08-24
    Description: The present study illustrates the inflatable sphere's capability to produce accurate temperatures up to 85 km and higher, given that the necessary reduction initialization conditions are met. At heights below 60 km, comparison of sphere temperatures with in situ thermistor measurements obtained close in space and time shows good agreement. Comparison with OH-radical rotational temperatures also confirms excellent agreement at 86 km. It is concluded that the sphere technique is an independent and highly accurate source of temperature measurement, is unique in being the only low-cost source of in situ measurement of temperature throughout the mesosphere and lower thermosphere, and qualifies as an intrinsic method to establish the accuracy of other atmosphere measurement systems.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 22
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    Error analysis of image reconstruction by a synthetic aperture interferometric radiometer (1991)
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    Publication Date: 2011-08-24
    Description: An error analysis is presented for the image reconstruction algorithm currently employed by the electronically steered thinned array radiometer aircraft instrument. This instrument samples components of the Fourier transform of the brightness temperature distribution at 1.4 GHz. Sources of error are identified, including systematic offsets and stochastic noise in the measurements, errors in the interference pattern antenna calibration, multipath scattering from the antenna support structure, mutual coupling between nearby array elements, and variations in the antenna patterns of the array elements. These errors are shown to produce artifacts in the image which appear as 'streaks' running along the instrument flight line. Possible hardware corrections are discussed. These include a reduction in the profile of the antenna support structure and a decoupling of adjacent and other nearby array elements using corrugated 'skirts'. Also discussed are several image enhancement techniques which detect and correct for some of the streaking. These techniques include a renormalization of the interference patterns based on the measured element patterns, a perturbation based interpretation of image contrast, and a covariance analysis of noise present in the image.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Radio Science (ISSN 0048-6604); 26; 1419-143
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    Static aeroelastic analysis for generic configuration wing (1991)
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    Publication Date: 2011-08-24
    Description: A static aeroelastic analysis capability that calculates flexible air loads for generic configuration wings was developed. It was made possible by integrating a finite element structural analysis code (MSC/NASTRAN) and a panel code of aerodynamic analysis based on linear potential flow theory. The framework already built in MSC/NASTRAN was used, and the aerodynamic influence coefficient matrix was computed externally and inserted in the NASTRAN by means of a DMAP program. It was shown that deformation and flexible air loads of an oblique wing configuration including asymmetric wings can be calculated reliably by this code both in subsonic and supersonic speeds.
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 28; 801
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    Numerical prediction of subsonic turbulent flows over slender bodies at high incidence (1991)
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    Publication Date: 2011-08-24
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 29; 2054-206
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    Probe systems for static pressure and cross-stream turbulence intensity (1991)
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    Publication Date: 2011-08-24
    Description: A recent study of total-pressure probes for use in highly turbulent streams is extended herein by developing probe systems that measure time-averaged static or ambient pressure and turbulence intensity. Arrangements of tubular probes of circular and elliptical cross section are described that measure the pressure at orifices on the sides of the probes to obtain different responses to the cross-stream velocity fluctuations. When the measured data are combined to remove the effect of the presence of the probes on the local pressure, the time-averaged static pressure and the cross-stream components of turbulence intensity can be determined. If a system of total pressure tubes, as described in an accompanying paper, is added to the static pressure group to form a single cluster, redundant measurements are obtained that permit accuracy and consistency checks.
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 28; 750-755
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    Characteristics of a dynamic holographic sensor for shape control of a large reflector (1991)
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    Publication Date: 2011-08-24
    Description: Design of a distributed holographic interferometric sensor for measuring the surface displacement of a large segmented reflector is proposed. The reflector's surface is illuminated by laser light of two wavelengths and volume holographic gratings are formed in photorefractive crystals of the wavefront returned from the surface. The sensor is based on holographic contouring with a multiple frequency source. It is shown that the most stringent requirement of temporal stability affects both the temporal resolution and the dynamic range. Principal factor which limit the sensor performance include the response time of photorefractive crystal, laser power required to write a hologram, and the size of photorefractive crystal.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Sensors and sensor integration; Proceedings of the Meeting, Orlando, FL, Apr. 4, 1991 (A93-21961 07-35); p. 2-10.
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    Palladium-chromium static strain gage for high temperature propulsion systems (1991)
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    Publication Date: 2011-08-24
    Description: The present electrical strain gage for high temperature static strain measurements is in its fine-wire and thin-film forms designed to be temperature-compensated on any substrate material. The gage element is of Pd-Cr alloy, while the compensator is of Pt. Because the thermally-induced apparent strain of this compensated wire strain gage is sufficiently small, with good reproducibility between thermal cycles to 800 C, output figures can be corrected within a reasonable margin of error.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Annual Health Monitoring Conference for Space Propulsion Systems, 3rd, Cincinnati, OH, Nov. 13, 14, 1991, Proceedings (A93-16401 04-20); p. 391-400.
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    Fabrication of thin film heat flux sensors (1991)
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    Publication Date: 2011-08-24
    Description: Thin-film heat-flux sensors have been constructed in the form of arrays of thermocouples on upper and lower surfaces of an insulating layer, so that flux values are proportional to the temperature difference across the upper and lower surface of the insulation material. The sensor thermocouples are connected in thermopile arrangement, and the structure is patterned with photolithographic techniques. Both chromel-alumel and Pt-Pt/Rh thermocouples have been devised; the later produced 28 microvolts when exposed to the radiation of a 1000 C furnace.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Annual Health Monitoring Conference for Space Propulsion Systems, 3rd, Cincinnati, OH, Nov. 13, 14, 1991, Proceedings (A93-16401 04-20); p. 356-365.
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    Implicit flux-split Euler schemes for unsteady aerodynamic analysis involving unstructured dynamic meshes (1991)
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    Publication Date: 2011-08-24
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 29; 1836-184
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    Viscous flow solutions for slender bodies of revolution at incidence (1991)
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    Publication Date: 2011-08-24
    Description: Flow over slender prolate spheroids at incidence is examined. The incidence angle is chosen high enough to cause streamwise separation of the flow in addition to crossflow separation generally observed at lower incidence angles. The freestream Mach number for the cases investigated here is subsonic, thus precluding the use of parabolized procedures. Laminar, transitional and turbulent flow cases are investigated.
    Keywords: AERODYNAMICS
    Type: Computers and Fluids (ISSN 0045-7930); 20; 3, 19
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    Thermochemical nonequilibrium issues for earth re-entry of Mars mission vehicles (1991)
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    Publication Date: 2011-08-24
    Keywords: AERODYNAMICS
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 28; 552-559
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    Aeroassist flight experiment heating-rate sensitivity study (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Keywords: AERODYNAMICS
    Type: Journal of Thermophysics and Heat Transfer (ISSN 0887-8722); 5; 456-462
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    A high data rate recorder for astronomy (1991)
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    Publication Date: 2011-08-19
    Description: A magnetic tape recorder developed for the special requirements of radio astronomy and geodesy is described. These requirements include a high bit packing density and long record times. The current version of this longitudinal recorder used by the Very Long Baseline Array (VLBA) records 5.5 Terabits on a 14-in diameter reel of inch-wide tape. A maximum record rate of 256 Mb/s is achieved in the VLBA configuration with one recorder operating at 4 ms and utilizing 32 of the heads in a single stack. The VLBA recorders have been tested using a longitudinal density of 2.25 fr/micron; 448 data + 56 system tracks are recorded in 14 passes, each lasting 50 min, for a total record time (at 128 Mb/s) of 12 h on 14-in diameter reel of inch-wide 13-microns-thick D1-equivalent tape.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: IEEE Transactions on Magnetics (ISSN 0018-9464); 27; 3455-346
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    Low energy positron flux generator for lifetime studies in thin films (1991)
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    Publication Date: 2011-08-19
    Description: A slow positron flux generator for positron annihilation spectroscopic measurements in thin polymer films is described. The advantages of this generator include operability at room temperature and atmospheric pressure without special test film preparaton requirements.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Nuclear Instruments and Methods in Physics Research, Section B - Beam Interactions with Materials and Atoms (ISSN 0168-583X); B53; 342-348
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    A planar Mie scattering technique for visualizing supersonic mixing flows (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A planar Mie scattering technique is described which allows for the direct visualization of fluid mixing in supersonic flows. The mixed fluid is visualized by laser light sheet scattering from small alcohol droplets which condense as a result of the mixing of a vapor laden subsonic stream with a cold supersonic stream. Issues related to the formation, growth and size of the droplets are addressed. The technique reveals details of the turbulent structure which are masked by the spatial integration of schlieren and shadowgraph methods. Comparative visualizations using the vapor screen method to uniformly mark the high-speed fluid are also shown.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Experiments in Fluids (ISSN 0723-4864); 11; 2-3,; 175-185
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    Effect of geometrical disturbance on vortex asymmetry (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 29; 560-566
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    Flight stagnation-point heating calculations on Aeroassist Flight Experiment vehicle (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: NASA's Aeroassist Flight Experiment (AFE) vehicle will be deployed from the Space Shuttle Orbiter in 1994 to make a data-gethering aeropass through the upper atmosphere before returning to orbit for Shuttle pickup. An axisymmetric, chemically-reacting viscous shock-layer code is presently used to calculate AFE heating rates which automatically accounts for the viscous-inviscid interaction and entropy layer-swallowing effects which are ignored by the conventional boundary-layer methods. Results are presented for the stagnation-point heating of the current AFE baseline trajectory.
    Keywords: AERODYNAMICS
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 28; 125-128
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    Supersonic aerodynamic characteristics of monoplanar missiles with low-profile quadriform tails (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 28; 9-15
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    Fully coupled implicit method for thermochemical nonequilibrium air at suborbital flight speeds (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 28; 31-39
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    Calorimetric output power measurements on a CW 20 kW 7.16 GHz microwave transmitter (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A calorimetric measurement technique developed for NASA's Deep Space Network (DSN) transmitters that does not require data on the coolant's thermal parameters is described. Calibration of the measurement system is achieved by measuring the DC input power to the klystron and relating coolant temperature increases to this known power dissipation. Agreement between calorimetric and electrical measurements of total system power was good, the difference being less than 2 percent. The operation of the system was not greatly affected by the composition of the coolant, which was varied from pure water to 40 percent ethylene glycol by mass. Good accuracy was also shown at output power levels, which varied over a 3.6:1 range.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: IEEE Transactions on Instrumentation and Measurement (ISSN 0018-9456); 40; 49-51
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    Dynamic edge warping - An experimental system for recovering disparity maps in weakly constrained systems (1991)
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    Publication Date: 2011-08-19
    Description: Dynamic edge warping (DEW), a technique for recovering reasonably accurate disparity maps from uncalibrated stereo image pairs, is presented. No precise knowledge of the epipolar camera geometry is assumed. The technique is embedded in a system including structural stereopsis on the front end and robust estimation in digital photogrammetry on the other for the purpose of self-calibrating stereo image pairs. Once the relative camera orientation is known, the epipolar geometry is computed and the system can use this information to refine its representation of the object space. Such a system will find application in the autonomous extraction of terrain maps from stereo aerial photographs, for which camera position and orientation are unknown a priori, and for online autonomous calibration maintenance for robotic vision applications, in which the cameras are subject to vibration and other physical disturbances after calibration. This work thus forms a component of an intelligent system that begins with a pair of images and, having only vague knowledge of the conditions under which they were acquired, produces an accurate, dense, relative depth map. The resulting disparity map can also be used directly in some high-level applications involving qualitative scene analysis, spatial reasoning, and perceptual organization of the object space. The system as a whole substitutes high-level information and constraints for precise geometric knowledge in driving and constraining the early correspondence process.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: IEEE Transactions on Systems, Man, and Cybernetics (ISSN 0018-9472); 21; 143-158
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    A long-range laser velocimeter (1991)
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    Publication Date: 2011-08-19
    Description: A long-range laser velocimeter (LV) developed for remote operation from within the flow fields of large wind tunnels is described. Emphasis is placed on recent improvements in optical hardware as well as recent additions to data acquisition and processing techniques. The method used for data reduction of photon resolved signals is outlined in detail, and measurement accuracy is discussed. To study the performance of the LV and verify the measurement accuracy, laboratory measurements were made in the flow field of a 10-cm-diameter, 30-m/s axisymetric jet. The measured velocity and turbulence intensity surveys are compared with measurements made with a hot-wire anemometer. Additionally, the LV was used during the flow calibration of the 80-ft x 120-ft wind tunnel to measure the test-section boundary-layer thickness at the maximum wind tunnel speed of 51.5 m/s. The requirements and techniques used to seed the flow are discussed, and boundary-layer surveys of mean velocity and turbulence intensity of the streamwise component and the component normal to the surface are presented. The streamwise component of mean velocity is compared with data obtained with a total pressure rake.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: IEEE Transactions on Aerospace and Electronic Systems (ISSN 0018-9251); 27; 125-138
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    Observations of dynamic stall phenomena using liquid crystal coatings (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Novel, shear stress-sensitive/temperature-insensitive liquid crystal coatings have been applied to the surface of an oscillating airfoil in order to ascertain the unsteady fluid physics associated with the dynamic-stall process. Surface microtufts and laser sheet/smoke-particle flow visualization were used to compare the liquid-crystal results. Boundary-layer transition and turbulent separation locations were measured as a function of geometric angle of attack. The results obtained are compared with Eppler (1980) aerodynamic design code predictions.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: AIAA Journal (ISSN 0001-1452); 29; 308-310
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    SiGe/Si heterojunction internal photoemission long-wavelength infrared detectors fabricated by molecular beam epitaxy (1991)
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    Publication Date: 2011-08-19
    Description: A new SiGe/Si heterojunction internal photoemission (HIP) long-wavelength infrared (LWIR) detector has been fabricated by molecular beam epitaxy (MBE). The detection mechanism of the SiGe/Si HIP detector is infrared absorption in the degenerately doped p+-SiGe layer followed by internal photoemission of photoexcited holes over a heterojunction barrier. By adjusting the Ge concentration in the SiGe layer, and, consequently, the valence band offset between SiGe and Si, the cutoff wavelength of SiGe HIP detectors can be extended into the LWIR (8-17-micron) regime. Detectors were fabricated by growing p+-SiGe layers using MBE on patterned p-type Si substrates. The SiGe layers were boron-doped, with concentrations ranging from 10 to the 19th/cu cm to 4 x 10 to the 20th/cu cm. Infrared absorption of 5-25 percent in a 30-nm-thick p+-SiGe layer was measured in the 3-20-micron range using a Fourier transform infrared spectrometer. Quantum efficiencies of 3-5 percent have been obtained from test devices in the 8-12-micron range.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: IEEE Transactions on Electron Devices (ISSN 0018-9383); 38; 1141-114
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    802GHz integrated horn antennas imaging array (1991)
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    Publication Date: 2011-08-19
    Description: Pattern measurements at 802GHz of a single element in 256-element integrated horn imaging array are presented. The integrated-horn antenna consists of a dipole-antenna suspended on a 1-micron dielectric membrane inside a pyramidal cavity etched in silicon. The theoretical far-field patterns, calculated using reciprocity and Floquet-modes representation of the free-space field, agree well with the measured far-field patterns at 802GHz. The associated directivity for a 1.40 lambda horn aperture, calculated from the measured E and H-plane patterns is 12.3dB + or - 0.2dB. This work demonstrates that high-efficiency integrated-horn antennas are easily scalable to terahertz frequencies and could be used for radio-astronomical and plasma-diagnostic applications.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: International Journal of Infrared and Millimeter Waves (ISSN 0195-9271); 12; 481-486
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    A C-band scatterometer for remote sensing the air-sea interface (1991)
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    Publication Date: 2011-08-19
    Description: An airborne C-band scatterometer system (C-Scat) has been developed to remotely sense ocean surface winds and improve upon the present understanding of the relationship between normalized radar cross section (NRCS) and ocean surface roughness influences such as wind speed and direction, wave height and slope, and the air-sea temperature difference. The scatterometer utilizes a unique frequency-steered microstrip array antenna that is installed beneath the fuselage of an airplane. The antenna is electronically scanned in elevation, from 20 deg to 50 deg off-nadir, and mechanically spins in azimuth. The system is capable of measuring ocean surface NRCS from altitudes as high as 25,000 ft. The transmitter and receiver operate from 4.98 to 5.7 GHz. System parameters such as transmitter pulse width, pulse repetition frequency, output power level, and receiver bandwidth are programmable. Received signals can be averaged and displayed in real time and are stored on a Winchester disk drive for post-flight analysis. Preliminary flight data that demonstrates the instrument's performance is presented.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); 29; 260-267
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    Numerical simulation of Shuttle ascent transonic flow using an unstructured-grid approach (1991)
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    Publication Date: 2011-08-19
    Description: An unstructured-grid, finite-volume method has been developed for simulating the inviscid flow over spacecrafts of realistic configuration. The grid generation is accomplished by a new technique on the basis of the advancing-front concept. This simple technique is shown to be equally as powerful for a complex multibody as for a single vehicle. Second- or third-order accuracy is obtained via an innovative interpolation procedure similar to the conventional MUSCL approach. This method has been applied to the Shuttle orbiter and a representative Shuttle launch vehicle consisting of the orbiter, the external tank, and the solid rocket boosters. A comparison is discussed between the present results and other results obtained from structured- and unstructured-grid methods.
    Keywords: AERODYNAMICS
    Type: Computers and Structures (ISSN 0045-7949); 39; 1-2,
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    Structural stereopsis - Potential for automatic stereo camera calibration (1991)
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    Publication Date: 2011-08-19
    Description: The paper describes the use of extended edge features as a source of primitives for structural stereopsis and considers the design of a system for autonomous camera calibration. It is shown that the structural approach permits greater use of spatial relational constraints, eliminating the coarse-to-fine tracking of point-based algorithms. Experimental results concerning matching and calibration on real images using Laplacian-of-Gaussian contour fragments as primitives in structural stereopsis are presented, and results in graph-theoretic representation and inexact matches, analytical photogrammetry, and other computer vision and image analysis problem domains are examined. Such a system might be used in aerial photogrammetry and cartography, and robotic vision systems; however, the system is still very much under development.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Optical Engineering (ISSN 0091-3286); 30; 288-299
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    Use of rotating pinholes and reticles for calibration of cloud droplet instrumentation (1991)
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    Publication Date: 2011-08-19
    Description: Calibration devices for the Forward Scattering Spectrometer Probe (FSSP) and the Optical Array Probe (OAP) were developed. The device used with the FSSP is a rotating pinhole calibrator. It utilizes light diffracted by a pinhole of a known diameter to simulate scattered light from a water droplet. This device can be used to calibrate the FSSP, measure the FSSP's optical collection angles and for instrument alignment and troubleshooting. The device used with the OAP is a rotating reticle calibrator. Chrome disks of a known diameter on the reticle are used for calibration of the OAP and for determining the OAP's response to out-of-focus particles in the probe volume.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Journal of Atmospheric and Oceanic Technology (ISSN 0739-0572); 8; 166-171
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    Newton's method applied to finite-difference approximations for the steady-state compressible Navier-Stokes equations (1991)
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    Publication Date: 2011-08-19
    Description: Finite-difference approximations for steady-state compressible Navier-Stokes equations, whose two spatial dimensions are written in generalized curvilinear coordinates and strong conservation-law form, are presently solved by means of Newton's method in order to obtain a lifting-airfoil flow field under subsonic and transonnic conditions. In addition to ascertaining the computational requirements of an initial guess ensuring convergence and the degree of computational efficiency obtainable via the approximate Newton method's freezing of the Jacobian matrices, attention is given to the need for auxiliary methods assessing the temporal stability of steady-state solutions. It is demonstrated that nonunique solutions of the finite-difference equations are obtainable by Newton's method in conjunction with a continuation method.
    Keywords: AERODYNAMICS
    Type: Journal of Computational Physics (ISSN 0021-9991); 93; 108-127
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    Micromachined silicon tunnel sensor for motion detection (1991)
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    Publication Date: 2011-08-19
    Description: The extreme sensitivity of electron tunneling to variations in electrode separation has been used to construct a novel, compact displacement transducer. Electrostatic forces are used to control the separation between the tunneling electrodes, thereby eliminating the need for piezoelectric actuators. The entire structure is composed of micromachined silicon single crystals, including a folded cantilever spring and a tip. Measurements of displacement sensitivity and noise are reported. This device offers a substantial improvement over conventional technology for applications which require compact, highly sensitive transducers.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Applied Physics Letters (ISSN 0003-6951); 58; 100-102
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    Ultrasonic velocity technique for monitoring property changes in fiber-reinforced ceramic matrix composites (1991)
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    Publication Date: 2011-08-19
    Description: A technique for measuring ultrasonic velocity was used to monitor changes that occur during processing and heat treatment of a SiC/RBSM composite. Results indicated that correlations exist between the ultrasonic velocity data and elastic modulus and interfacial shear strength data determined from mechanical tests. The ultrasonic velocity data can differentiate strength. The advantages and potential of this nondestructive evaluation method for fiber reinfoced ceramic matrix composite applications are discussed.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Ceramic Engineering and Science Proceedings (ISSN 0196-6219); 12; 1139-115
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    A simplified wind vector algorithm for satellite scatterometers (1991)
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    Publication Date: 2011-08-19
    Description: A simplified algorithm is derived for retrieving wind vectors from microwave scatterometer observations. The azimuthal dependence of the sea-surface radar cross section is modeled by a double-cosine function, rather than the traditional second-order cosine expansion. The algorithm is tested using the aircraft scatterometer observations obtained during the AAFE-RADSCAT Experiment in 1975 and 1976. There is little difference between the performance of the simplified algorithm and the more involved least-squares searching algorithm. The AAFE-RADSCAT aircraft observations are sampled so as to simulate the three-look satellite scatterometer NSCAT that will be launched on the Japanese Advanced Earth Observing Satellite. The results of the retrievals indicate that it is probably not possible to uniquely determine the wind direction using just NSCAT observations because of a 180 degree ambiguity. However, if forecast models can predict the wind direction to an accuracy of +/- 90 deg, thereby eliminating the ambiguity, then the results indicate that NSCAT can determine the wind direction to an accuracy of about +/- 20 deg. Better performance is obtained when the three observations are the same polarization (either v-pol or h-pol), as compared to using a mix of v-pol and h-pol observations.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Journal of Atmospheric and Oceanic Technology (ISSN 0739-0572); 8; 697-704
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    Laser-induced fluorescence measurements of flow velocity in high-power arcjet thruster plumes (1991)
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    Publication Date: 2011-08-19
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: AIAA Journal (ISSN 0001-1452); 29; 1298-130
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    Experimental transition investigation of a free-shear layer above a cavity at Mach 3.5 (1991)
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Propulsion and Power (ISSN 0748-4658); 7; 626-634
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    Influence of thickness and camber on the aeroelastic stability of supersonic throughflow fans (1991)
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    Publication Date: 2011-08-19
    Description: An engineering approach was used to include the nonlinear effects of thickness and camber in an analytical aeroelastic analysis of casecades in supersonic acial flow (supersonic leading-edge locus). A hybrid code using Lighthill's nonlinear piston theory and Lane's linear potential theory was developed to include these nonlinear effects. Lighthill's theory was used to calculate the unsteady pressures on the noninterference surface regions of the airfoils in cascade. Lane's theory was used to calculate the unsteady pressures on the remaining interference surface regions. Two airfoil profiles were investigated (a supersonic throughflow fan design and a NACA 66-206 airfoil with a sharp leading edge). Results show that compared with predictions of Lane's potential theory for flat plates, the inclusion of thickness (with or without camber) may increase or decrease the aeroelastic stability, depending on the airfoil geometry and operating conditions. When thickness effects are included in the aeroelastic analysis, inclusion of camber will influence the predicted stability in proportion to the magnitude of the added camber. The critical interblade phase angle, depending on the airfoil profile and operating conditions, may also be influenced by thickness and camber. Compared with predictions of Lane's linear potential theory, the inclusion of thickness and camber decreased the aerodynamic stiffness and increased the aerodynamic damping at Mach 2 and 2.95 for a cascade of supersonic throughflow fan airfoils oscillating 180 degrees out of phase at a reduced frequency of 0.1.
    Keywords: AERODYNAMICS
    Type: Journal of Propulsion and Power (ISSN 0748-4658); 7; 404-411
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    A new system model for radar polarimeters (1991)
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    Publication Date: 2011-08-19
    Description: The validity of the 2 x 2 receive R and transmit T model for radar polarimeter systems, first proposed by Zebker et al. (1987), is questioned. The model is found to be invalid for many practical realizations of radar polarimeters, which can lead to significant errors in the calibration of polarimetric radar images. A more general model is put forward, which addresses the system defects which cause the 2 x 2 model to break down. By measuring one simple parameter from a polarimetric active radar calibration (PARC), it is possible to transform the scattering matrix measurements made by a radar polarimeter to a format compatible with a 2 x 2 R and T matrix model. Alternatively, the PARC can be used to verify the validity of the 2 x 2 model for any polarimetric radar system. Recommendations for the use of PARCs in polarimetric calibration and to measure the orientation angle of the horizontal (H) and vertical (V) coordinate system are also presented.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); 29; 761-767
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    A spectral collocation method for compressible, non-similar boundary layers (1991)
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    Publication Date: 2011-08-19
    Description: An efficient and highly accurate algorithm based on a spectral collocation method is developed for numerical solution of the compressible, two-dimensional and axisymmetric boundary layer equations. The numerical method incorporates a fifth-order, fully implicit marching scheme in the streamwise (timelike) dimension and a spectral collocation method based on Chebyshev polynomial expansions in the wall-normal (spacelike) dimension. The spectral collocation algorithm is used to derive the nonsimilar mean velocity and temperature profiles in the boundary layer of a 'fuselage' (cylinder) in a high-speed (Mach 5) flow parallel to its axis. The stability of the flow is shown to be sensitive to the gradual streamwise evolution of the mean flow and it is concluded that the effects of transverse curvature on stability should not be ignored routinely.
    Keywords: AERODYNAMICS
    Type: International Journal for Numerical Methods in Fluids (ISSN 0271-2091); 13; 713-737
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    Numerical simulation of high-incidence flow over the F-18 fuselage forebody (1991)
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 28; 609-617
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    A wide-band monolithic quasi-optical power meter for millimeter- and submillimeter-wave applications (1991)
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    Publication Date: 2011-08-19
    Description: A novel monolithic power meter has been developed for submillimeter-wave applications (100 GHz to 10 THz). The detector is a large-area bismuth bolometer integrated on a 1.2-micron-thick dielectric membrane. This approach results in a wide-band, high-responsivity detector. The power meter is simple to fabricate, is inexpensive, and can be easily calibrated using a low-frequency network. Quasi-optical measurements at 90, 140, and 240 GHz show that the bolometer is polarization-independent and could be modeled by a simple transmission line model. Absolute power measurements at 90, 140, and 240 GHz show a + or - 5 percent accuracy and agree well with a calibrated Anritsu power meter at 90 GHz. Potential application areas are power calibration, antenna coupling efficiency measurements, and absolute power measurements from solid-state devices and far-infrared lasers at submillimeter wavelengths. Absolute output power measurements on a 220-280 GHz tripler using the quasi-optical power meter are presented as an application example.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: IEEE Transactions on Microwave Theory and Techniques (ISSN 0018-9480); 39; 1257-126
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    Computation of Navier-Stokes equations for three-dimensional flow separation (1991)
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    Publication Date: 2011-08-19
    Description: Supersonic flows over a sharp and a flat-faced blunt fin mounted on a flat plate are simulated numerically. Several basic issues involved in the resultant three-dimensional steady flow separation are studied. Using the same number of grid points, different grid spacings are employed to investigate the effects of a grid resolution on the origin of the line of separation. Various shock strengths are used to study the so-called separation and unseparated boundary layer and to establish the existence or absence of secondary separation. The length of separation ahead of the flat-faced blunt fin, bifurcation of a horseshoe vortex, and the accessibility of a closed-type separation are investigated. The usual interpretation of the flow field from previous studies and new interpretations arising from the present simulation are discussed.
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 29; 1659-166
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  • 86
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    Compressible equilibrium turbulent boundary layers at nonadiabatic wall conditions (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 29; 1573-158
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  • 87
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    Oscillation of high-altitude balloons (1991)
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    Publication Date: 2011-08-19
    Description: The Vaisala-Brunt frequencies of atmospheric waves lie sufficiently near He-filled balloon buoyancy oscillation frequencies to cause a near-resonance condition, especially in the 11.6-24.4 km altitude range. This excitation will hold for such balloons irrespective of size and payload variations due to the independence of balloon buoyant frequencies from size. Vertical perturbations of approximately 5-min period should accordingly be anticipated by balloon flight-control system designers.
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 28; 606-608
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  • 88
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    Aeroacoustic flow sensor (1991)
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    Publication Date: 2011-08-19
    Description: A theoretical analysis of standing waves in a pipe with flow was conducted aimed toward the development of a flowmeter based on a measurement of phase difference between two points on the circumference of a pipe separated axially by an integral multiple of half sound wavelength. Effects of nonzero Mach number, variable ratios of upstream and downstream running waves, choice of location of the sensing pressure taps, and the incorrect spacings were examined numerically. Calculations were also made for steam flow where the maximum Mach number is much smaller than in cold air flows. For an industrial application where steam flow velocities are below 50 m/s, a very accurate sensor is shown to be possible. Experimental data were obtained by using an active aeroacoustic source over the range of 50 m/s to zero in an air flow. Experimental phase plots obtained from several coast-down tests have been compared with analytical results. The agreement with theory is excellent when the spacings are near N(lambda)/2 and the sensing locations are near the pressure antinodes. Otherwise, some zero shifts are introduced. Theory predicts that for steam flow much better results can be expected because the maximum Mach number is much smaller. Effects due to the (1-M-squared) factor would be imperceptible for steam flow.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Review of Scientific Instruments (ISSN 0034-6748); 62; 2205-221
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  • 89
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    Effect of splitter plate on unsteady flows around a body of revolution at incidence (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Numerical solutions of the thin-layer approximation of the 3D Navier-Stokes equations are presented for flows around an ogive-cylinder body with and without a splitter plate. It is suggested that the presence of the splitter plate prevents the interaction between flows on either side of the symmetry plane. It is concluded that, as a result of the enforced symmetry, the antisymmetric mode of the convective instability near the apex of the body cannot be excited and, therefore, the vortices remain symmetric, staying low and parallel to the upper body surface. The antisymmetric mode of the absolute instability mechanism cannot be initiated, which suppresses the alternate shedding of vortices from the cylindrical portion of the body. High-frequency fluctuations of the shear layer are found to remain virtually unaffected by the presence of the splitter plate.
    Keywords: AERODYNAMICS
    Type: Physics of Fluids A (ISSN 0899-8213); 3; 2122-213
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  • 90
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    Effect of vortex core distortion on blade-vortex interaction (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 29; 1355-136
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  • 91
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    Flight tests of external modifications used to reduce blunt base drag (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 28; 517-525
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  • 92
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    Semianalytical technique for sensitivity analysis of unsteady aerodynamic computations (1991)
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 28; 481-488
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  • 93
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    Multiplex Fabry-Perot interferometer (1991)
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    Publication Date: 2011-08-19
    Description: Attention is given to a Fabry-Perot interferometer (FPI) technique in which one of the etalon plates is moved over a large optical distance while the other remains fixed, thus exploiting the multiplex advantage of the instrument. This technique involves the application of Fourier-transform spectrometer to the multiple harmonics passing through the FPI etalon. It is shown that the multiplex FPI acts as several Michelson interferometers working at the same time, over the same spectral interval, and at different spectral resolutions. A high spectral resolution has been obtained over a large wavenumber interval, while the advantage of a reasonable scan length has been retained.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Applied Optics (ISSN 0003-6935); 30; 3108-311
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  • 94
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    Hypersonic rarefied flow about plates at incidence (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 29; 1250-125
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  • 95
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    Computational and experimental evaluation of helicopter rotor tips for high-speed flight (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 28; 403-409
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  • 96
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    New device for controlling asymmetric flowfields on forebodies at large alpha (1991)
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 28; 456-462
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  • 97
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    Accuracy of an unstructured-grid upwind-Euler algorithm for the ONERA M6 wing (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Improved algorithms for the solution of the three-dimensional, time-dependent Euler equations are presented for aerodynamic analysis involving unstructured dynamic meshes. The improvements have been developed recently to the spatial and temporal discretizations used by unstructured-grid flow solvers. The spatial discretization involves a flux-split approach that is naturally dissipative and captures shock waves sharply with at most one grid point within the shock structure. The temporal discretization involves either an explicit time-integration scheme using a multistage Runge-Kutta procedure or an implicit time-integration scheme using a Gauss-Seidel relaxation procedure, which is computationally efficient for either steady or unsteady flow problems. With the implicit Gauss-Seidel procedure, very large time steps may be used for rapid convergence to steady state, and the step size for unsteady cases may be selected for temporal accuracy rather than for numerical stability. Steady flow results are presented for both the NACA 0012 airfoil and the Office National d'Etudes et de Recherches Aerospatiales M6 wing to demonstrate applications of the new Euler solvers. The paper presents a description of the Euler solvers along with results and comparisons that assess the capability.
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 28; 397-402
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  • 98
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    Numerical solutions of forward-flight rotor flow using an upwind method (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 28; 374-380
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  • 99
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    Experimental and predicted pressure and heating distributions for aeroassist flight experiment vehicle (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Thermophysics and Heat Transfer (ISSN 0887-8722); 5; 301-307
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  • 100
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    Computation of laminar hypersonic compression-corner flows (1991)
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 29; 1108-111
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