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At least 217 records · Page 12

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NASA NTRS1976

Heavy ions from the Galilean satellites and the centrifugal distortion of the Jovian magnetosphere

The Galilean satellites constitute a potentially significant source of plasma to the Jovian atmosphere. The paper examines the distortion of the Jovian magnetosphere that would result from injection of ions at the Galilean satellites. The magnetic distortion produced is a localized perturbation near the equatorial plane, in contrast to the large-scale distortion produced by Jovian atmospheric ions. The study estimates the relative perturbation currents resulting from the two sources in terms of the unknown ion production rate at the satellites. It is found that the two perturbations would be of comparable magnitudes if the ion source flux at all of the Galilean satellites were comparable to the photo-ion escape flux from Jupiter's atmosphere. More specifically, ions produced by the Galilean satellites should be confined near the equatorial plane of Jupiter's magnetosphere in a sheet whose thickness is determined by a centrifugal scale height given essentially by the ion thermal speed divided by the corotation frequency.

Hill, T. W.↗

NASA NTRS1978

Three-dimensional effects on pure tone fan noise due to inflow distortion

A theoretical analysis of pure tone fan noise generated by inflow distortion-rotor interaction is carried out with the aid of the three-dimensional unsteady lifting surface theory developed by Namba (1977, 1974). Particular attention is given to a study of the accuracy of available two-dimensional theory for the prediction of pure tone fan noise due to the interaction of inflow distortion with a subsonic annular blade row. The theoretical model considered consists of a single three-dimensional annular cascade rotating at constant angular velocity in an annular rigid-wall duct of infinite axial extent. Attention is given to the fluctuating pressure induced by a rotor blade row, the fluctuating velocity induced by it, an inflow distortion with only an axial velocity component, the determination of acoustic dipole distribution, the pure tone acoustic power, and two-dimensional theory and quasi-three-dimensional theory.

Kobayashi, H.↗

NASA NTRS1978

Estimating maximum instantaneous distortion from inlet total pressure rms measurements

In the present paper, a new mathematical model of inlet turbulence is developed by application of basic fluid dynamics and statistical concepts. The model provides an understanding of the turbulent inlet flow as well as a means of describing the flow in quantitative terms. Specifically, the maximum instantaneous distortion produced by inlet unsteady flow can be estimated by the simple measurement of rms data. Practical application of these techniques leads to a data/acquisition/reduction system that is at least one, and maybe two, orders of magnitude less expensive than conventional methods. Each data point can be reduced in terms of the mean strength of the turbulent vortices. By storing these two parameters (that are representative of the unsteady flow with the steady state information), the maximal instantaneous distortion can be reconstructed for other distortion factors at any time subsequent to the test.

Melick, H. C., Jr.↗

NASA NTRS1978

Measurements of inlet flow distortions in an axial flow fan (6 and 9 blade rotor)

A large quantity of experimental data on inlet flow distortions in an axial flow fan were obtained. The purpose of the study was to determine the effects of design and operating variables and the type of distortion on the response of an axial flow turbomachinery rotor. Included are background information and overall trends observed in distortion attenuation and unsteady total pressure losses.

Barr, L. C.↗

NASA NTRS1979

Experimental evaluation of the effect of inlet distortion on compressor blade vibrations

Compressor rotor strain gage data from an engine test conducted with an inlet screen distortion were reduced and analyzed. These data are compared to data obtained from the same engine without inlet pressure distortion to determine the net effect of the distortion on the vibratory response of the compressor blades. The results obtained are presented.

Lubomski, J. F.↗

NASA NTRS1979

Effect of number of probes and their orientation on the calculation of several compressor face distortion descriptors

A study was performed to determine the effects of the number and position of total pressure probes on the calculation of five compressor face distortion descriptors. This study used three sets of 320 steady state total pressure measurements that were obtained with a special rotating rake apparatus in wind tunnel tests of a mixed-compression inlet. The inlet was a one third scale model of the inlet on a YF-12 airplane, and it was tested in the wind tunnel at representative flight conditions at Mach numbers above 2.0. The study shows that large errors resulted in the calculation of the distortion descriptors even with a number of probes that were considered adequate in the past. There were errors as large as 30 and -50 percent in several distortion descriptors for a configuration consisting of eight rakes with five equal-area-weighted probes on each rake.

Stoll, F.↗

NASA NTRS1979

Effects of steady-state pressure distortion on the stall margin of a J85-21 turbojet engine

The effects of the inlet pressure distortions, induced by five screen patterns, on the performance of a J85-21 turbojet engine was conducted at the NASA Lewis Research Center. Testing was in support of the HiMAT RPRV program at Dryden Flight Research Center. Distortion patterns were chosen based on anticipated application of test results of the HiMAT installation. Tests were conducted at a simulated Mach number and altitude condition of 0.9 and 10 973 meters. Results are presented in terms of distortion levels and standard compressor performance parameters.

Bobula, G. A.↗

NASA NTRS1979

Minimizing the RMS surface distortions from gravity loadings of the 34-m HA-DEC antenna for deep space missions

The computer analysis of the 34-m HA-DEC antenna by the IDEAS program provided the rms distortions of the surface panels support points for full gravity loadings in the three directions of the basic coordinate system of the computer model. The rms distortions for the gravity vector not in line with any of the three basic directions were solved and contour plotted starting from three surface panels setting declination angle. By inspections of the plots, it was concluded that the setting or rigging angle of -15 degrees declination minimized the rms distortions for sky coverage of plus or minus 22 declination angles to 10 degrees of ground mask.

Katow, S. M.↗

NASA NTRS1978

Unsteady vortical and entropic distortions of potential flows round arbitrary obstacles

The analysis concerns the alterations produced when small amplitude disturbances, including entropy and vorticity disturbances, are imposed on steady potential flows. For the most general nonacoustic incident distortion field that can be imposed on the uniform upstream flow, it is shown that the perturbation velocity at any point of the resulting unsteady compressible and vortical flow consists of a part that is a known function of the imposed upstream distortion field and the mean flow variables and a potential part that can be found by solving a linear inhomogeneous wave equation with a dipole-type source term whose strength is a known function of the imposed upstream distortion field. The theory is applied to the unsteady flow past a corner, and a closed-form analytical solution is found.

Goldstein, M. E.↗

NASA NTRS1980

Application of optimum smoothing for image distortion correction

Optimum linear smoothing is utilized to estimate certain distortions in LANDSAT-D images. Measurements that are processed by the smoother consist of designated control of point locations within the images. Image distortions that are estimated by the smoother are those induced by LANDSAT-D satellite navigation errors and slowly varying attitude and sensor alignment uncertainties. Preliminary results indicate that optimum smoothing produces substantially more accurate distortion estimates than optimum filtering and that optimum smoothing may reduce the number of control points needed to yield desired image correction accuracy.

Werner, R. A.↗

NASA NTRS1983

Literature search of publications concerning the prediction of dynamic inlet flow distortion and related topics

Publications prior to March 1981 were surveyed to determine inlet flow dynamic distortion prediction methods and to catalog experimental and analytical information concerning inlet flow dynamic distortion prediction methods and to catalog experimental and analytical information concerning inlet flow dynamics at the engine-inlet interface of conventional aircraft (excluding V/STOL). The sixty-five publications found are briefly summarized and tabulated according to topic and are cross-referenced according to content and nature of the investigation (e.g., predictive, experimental, analytical and types of tests). Three appendices include lists of references, authors, organizations and agencies conducting the studies. Also, selected materials summaries, introductions and conclusions - from the reports are included. Few reports were found covering methods for predicting the probable maximum distortion. The three predictive methods found are those of Melick, Jacox and Motycka. The latter two require extensive high response pressure measurements at the compressor face, while the Melick Technique can function with as few as one or two measurements.

Schweikhhard, W. G.↗

NASA NTRS1984

Distortion measurement of antennas under space simulation conditions with high accuracy and high resolution by means of holography

The use of laser holography for measuring the distortion of antennas under space simulation conditions is described. The subject is the so-called double exposure procedure which allows to measure the distortion in the order of 1 to 30/micrometers + or - 0.5 per hologramme of an area of 4 m diameter max. The method of holography takes into account the constraints of the space simulation facility. The test method, the test set up and the constraints by the space simulation facility are described. The results of the performed tests are presented and compared with the theoretical predictions. The test on the K-Band Antenna e.g., showed a distortion of approximately 140/micrometers + or - 5/micrometers measured during the cool down from -10 C to -120 C.

Frey, H. U.↗

NASA NTRS1985

Effect of Steady-State Temperature Distortion on Inlet Flow to a High-Bypass-Ratio Turbofan Engine

The effects of circumferential inlet temperature distortion on the flow characteristics between a distortion generator and a high bypass ratio turbofan engine and through its compression system were evaluated to support the effort to generate analytical models. The flow characteristics are defined by the inlet duct, the flow angles, and the total temperature, total pressure, and static pressure profiles in the inlet duct and through the fan and compressor. The effects of Reynolds number, rotor speed, and distortion extent are also considered.

Soeder, R. H.↗

NASA NTRS1985

Tests of Low-frequency Geometric Distortions in LANDSAT 4 Images

The geometric characteristics of LANDSAT 4 images were studied. The extent of image distortion caused by the physical process of writing the LANDSAT 4 images on film was determined. The geometric accuracies inherent in the digital images themselves were characterized. Test materials consisted of film images of test targets generated by the laser beam recorders (LBR), the Optronics Photowrite film writer, and digital image films of a strip 600 lines deep across the full width of band 5 of the Washington, D.C. Thematic Mapper scene. The tests were made by least squares adjustment of an array of measured image points to a corresponding array of control points. The film test array consists of 25 test points, and the image test array consists of 60 test points, resulting in a model that can be used to characterize the low frequency, random geometric distortions of the images. The tests were not suitable for examining jitter or similar high-frequency distortions.

Batson, R. M.↗

NASA NTRS1985

Effects of inlet distortion on a static pressure probe mounted on the engine hub in an F-15 airplane

An inlet static pressure (PS2) probe was mounted on the hub of an F100 engine in an F-15 airplane. Flight test results showed that for low distortion conditions, the ratio of engine-face total pressure to static pressure agreed well with previous altitude facility data. Off-schedule operation of the inlet third ramp angle caused increased distortion of the inlet airflow during steady-state flight conditions. Data are shown for inlet third ramp excursions leading to engine stall. The relationships of inlet face total to static pressure ratio as a function of several distortion descriptors are also described.

Hughes, D. L.↗

NASA NTRS1985

Recovery of pyroshock data from distorted acceleration records

In the past, distorted pyrotechnic shock time history data was discarded completely or cleaned up by questionable means. Too often the clean up procedures introduced as much error into the data as previously existed. Techniques are presented for data recovery so that true signals are obtained and so that these recovery procedures will be completely reproducible by any scientists in any lab. Most ordnance shock data is distorted by baseline shifts or accelerometer resonances. The methodology of recovering true signals from these two types of distortion is discussed.

Smith, J. L.↗

NASA NTRS1985

Evolution of rotationally and tidally distorted low-mass, close binary systems - Implications for the minimum orbital period of cataclysmic variables

A (1 + 0.4) solar mass close binary system consisting of a compact primary and a red dwarf secondary has been evolved numerically. Such a binary system should effectively model cataclysmic variables for which a minimum orbital period cutoff of about 81 minutes has been observed. The influence of gravitational radiation losses which drive Roche lobe overflow has been studied, and the effects of rotational and tidal distortion have also been incorporated in the calculation. The evolution of the He-3 abundance, which has been suggested as a possible explanation for the upper limit of the apparent orbital period gap exhibited by cataclysmic variables, is also considered. It is found that both the distortional effects and the He-3 chemical profile can play an important role in determining the subsequent evolution of these systems. Specifically, when distortion is included, the theoretical minimum orbital period is increased by about 10 percent, yielding better agreement with observations.

Nelson, L. A.↗

NASA NTRS1987

A study of the effect of group delay distortion on an SMSK satellite communications channel

The effects of group delay distortion on an SMSK satellite communications channel have been investigated. Software and hardware simulations have been used to determine the effects of channel group delay variations with frequency on the bit error rate for a 220 Mbps SMSK channel. These simulations indicate that group delay distortions can significantly degrade the bit error rate performance. The severity of the degradation is dependent on the amount, type, and spectral location of the group delay distortion.

Kerczewski, Robert J.↗