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At least 883 records · Page 49

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NASA NTRS1987

IUE observations of HL CMa and the winds of cataclysmic variables

As evidenced by the P Cygni profiles of their ultraviolet resonance lines, cataclysmic variables - like early-type stars - are known to have extensive, high velocity winds. Assisted by AAVSO visual data and IUE ultraviolet spectra, an observational and theoretical study of the P Cygni profiles of the dwarf nova HL CMa is presented. As these profiles are dependent upon the ionization structure of the wind, a model of a radiatively-driven shocked wind for cataclysmic variables is described, and results for the temperature and ionization structure of the outflowing gas are presented.

Mauche, C. W.↗

NASA NTRS1987

Experimental flowfield visualization of a high alpha wing at Mach 1.62

Experimental oil-flow and tuft patterns and vapor-screen flow-visualization data were obtained on a cambered wing model at Mach = 1.62 for an angle-of attack range of 0-14 deg. These data were used as flow diagnostic tools along with surface-pressure and force data and full-potential theory calculations. A large separation bubble was found on the lower wing surface at low angle of attack. The high-angle-of-attack flowfield was characterized by a large attached-flow leading-edge expansion followed by a crossflow shock. At alpha = 14 deg the crossflow shock apparently induced discrete regions of streamwise separated flow, which were clearly indicated in the vapor-screen and oil-flow photographs.

Pittman, James L.↗

NASA NTRS1987

Comparison of experimental and computational techniques for plane mixing layers

In this paper, results from two experimental and two computational investigations of plane turbulent mixing layers are presented and compared. The experimental results include flow visualization data using the smoke laser technique and mean flow and turbulence measurements obtained with hot X-wires and a two-component LDV. Reasonably good agreement is found among these techniques, at least for turbulence quantities up to second order. Reynolds-averaged computations are successful at capturing the complete evolution of the mixing layer, including wake effects in the near field and approach to self-preservation in the far field. The two-dimensional vortex method shows excellent qualitative and quantitative agreement with measured data for the forced mixing layer. For the unforced layer, the results seem to indicate that a three-dimensional computation may be necessary.

Mehta, R. D.↗

NASA NTRS1987

Planform effects on the supersonic aerodynamics of multibody configurations

An experimental and theoretical investigation of the effect of planform on the supersonic aerodynamics of low-fineness-ratio multibody configurations was conducted. Longitudinal and lateral-directional aerodynamic and flow visualization data were obtained on three multibody configurations. The data indicated that planform has a small effect on the zero lift drag of a multibody configuration. The longitudinal data obtained at lifting conditions showed a sensitivity to planform shape. Lateral-directional data obtained for all configurations did not uncover any unusual stability traits for this class of configuration. A comparison study was also made between the planform effects observed on single-body and multibody configurations. Results from this study indicate that the multibody concept appears to offer a mechanism for employing a low-sweep wing with no significant increase in zero-lift drag but still retaining high-performance characteristics at high-lift conditions. Evaluation of the linear-theory prediction methods revealed a general inability of the methods to predict the characteristics of low-fineness-ratio geometries.

Mcmillin, Naomi↗

NASA NTRS1987

Development of Moire machine vision

Three dimensional perception is essential to the development of versatile robotics systems in order to handle complex manufacturing tasks in future factories and in providing high accuracy measurements needed in flexible manufacturing and quality control. A program is described which will develop the potential of Moire techniques to provide this capability in vision systems and automated measurements, and demonstrate artificial intelligence (AI) techniques to take advantage of the strengths of Moire sensing. Moire techniques provide a means of optically manipulating the complex visual data in a three dimensional scene into a form which can be easily and quickly analyzed by computers. This type of optical data manipulation provides high productivity through integrated automation, producing a high quality product while reducing computer and mechanical manipulation requirements and thereby the cost and time of production. This nondestructive evaluation is developed to be able to make full field range measurement and three dimensional scene analysis.

Harding, Kevin G.↗

NASA NTRS1988

Machine vision for real time orbital operations

Machine vision for automation and robotic operation of Space Station era systems has the potential for increasing the efficiency of orbital servicing, repair, assembly and docking tasks. A machine vision research project is described in which a TV camera is used for inputing visual data to a computer so that image processing may be achieved for real time control of these orbital operations. A technique has resulted from this research which reduces computer memory requirements and greatly increases typical computational speed such that it has the potential for development into a real time orbital machine vision system. This technique is called AI BOSS (Analysis of Images by Box Scan and Syntax).

Vinz, Frank L.↗

NASA NTRS1987

The size, shape, density, and albedo of Ceres from its occultation of BD+8 deg 471

Photoelectric observations of BD+8 deg 471's November 13, 1984 occultation by Ceres show Ceres to be an oblate spheroid with a 479.6 + or - 2.4 km equatorial radius and 453.4 + or - 4.5 km polar radius. Despite the global appearance of a surface in hydrostatic equilibrium, real limb irregularities are distincly noticeable in the data. Visual geometric albedo is 0.073, and mean density 2.7 (+ or - 5 percent) g/cu cm.

Millis, R. L.↗

NASA NTRS1989

Flow-field characteristics and normal-force correlations for delta wings from Mach 2.4 to 4.6

An experimental investigation has been conducted to determine the upper-surface flowfield types and the normal-force characteristics of a series of delta wing models at supersonic speeds. Flow-visualization data were used to classify the flowfields into seven primary types: shockless attached flow, separation bubble, classical vortex, vortex with shock, shock with no separation, shock-induced separation, and separation bubble with shock. The pressure distributions were integrated to obtain upper and lower surface normal-force loadings. A minimal effect of sweep was observed on the upper-surface normal force at constant Mach number and a minimal effect of Mach number was noted for the 75 deg delta wing lower-surface normal force. The normal-force coefficients for all test conditions were correlated, and a single empirical equation was formulated from which the normal-force coefficient could be calculated as a function of Mach number, angle of attack, and wing aspect ratio.

Covell, Peter F.↗

NASA NTRS1991

Visualization of leading edge vortices on a series of flat plate delta wings

A summary of flow visualization data obtained as part of NASA Grant NAG2-258 is presented. During the course of this study, many still and high speed motion pictures were taken of the leading edge vortices on a series of flat plate delta wings at varying angles of attack. The purpose is to present a systematic collection of photographs showing the state of vortices as a function of the angle of attack for the four models tested.

Payne, Francis M.↗

NASA NTRS1991

A water tunnel flow visualization study of the vortex flow structures on the F/A-18 aircraft

The vortex flow structures occurring on the F/A-18 aircraft at high angles of attack were studied. A water tunnel was used to gather flow visualization data on the forebody vortex and the wing leading edge extension vortex. The longitudinal location of breakdown of the leading edge vortex was found to be consistently dependent on the angle of attack. Other parameters such as Reynolds number, model scale, and model fidelity had little influence on the overall behavior of the flow structures studied. The lateral location of the forebody vortex system was greatly influenced by changes in the angle of sideslip. Strong interactions can occur between the leading edge extension vortex and the forebody vortex. Close attention was paid to vortex induced flows on various airframe components of the F/A-18. Reynolds number and angle of attack greatly affected the swirling intensity, and therefore the strength of the studied vortices. Water tunnel results on the F/A-18 correlated well with those obtained in similar studies at both full and sub scale levels. The water tunnel can provide, under certain conditions, good simulations of realistic flows in full scale configurations.

Sandlin, Doral R.↗

NASA NTRS1990

An evaluation of various concepts of reducing supersonic jet noise

Acoustic and flow visualization data from nozzles mounted on the same facility were acquired, and a total of 10 different concepts of jet noise suppression were evaluated relative to one another and also a round nozzle. All nozzles had the same exit area. The suppressors included noncircular shapes; nozzles fitted with notches, tabs, and ejectors; and coaxial rectangular nozzles. Narrow-band noise data were acquired by a microphone located in the plane of the jet exit. In general, it is found that, for a constant exit area, the round nozzle is the noisiest. Just about any modification of this round nozzle around its periphery reduces the broadband shock-associated noise and, in most instances, modifies the screech frequency and levels. Coaxial rectangular nozzles, nozzles fitted with two tabs and operated with ejectors, and a rectangular C-D nozzles with perforated walls are identified to be the most promising concepts worthy of further investigation.

Ahuja, K. K.↗

NASA NTRS1991

Unsteady surface pressure measurements on a slender delta wing undergoing limit cycle wing rock

An experimental investigation of slender wing limit cycle motion known as wing rock was investigated using two unique experimental systems. Dynamic roll moment measurements and visualization data on the leading edge vortices were obtained using a free to roll apparatus that incorporates an airbearing spindle. In addition, both static and unsteady surface pressure data was measured on the top and bottom surfaces of the model. To obtain the unsteady surface pressure data a new computer controller drive system was developed to accurately reproduce the free to roll time history motions. The data from these experiments include, roll angle time histories, vortex trajectory data on the position of the vortices relative to the model's surface, and surface pressure measurements as a function of roll angle when the model is stationary or undergoing a wing rock motion. The roll time history data was numerically differentiated to determine the dynamic roll moment coefficient. An analysis of these data revealed that the primary mechanism for the limit cycle behavior was a time lag in the position of the vortices normal to the wing surface.

Arena, Andrew S., Jr.↗

NASA NTRS1991

A numerical and experimental study of tangential jet blowing applied to bodies at high angles of attack

The effects of tangential jet blowing on the vortical structures developing about the fuselage of a missile or aircraft at high angle of attack are investigated numerically and experimentally. Computations are carried out for fully laminar and fully turbulent flows, and the results are compared with flow visualization data. It is shown that turbulent computations are more accurate in describing the flow behavior. The actuator plane method is shown to be sufficiently accurate in modeling the essential flow physics of a tangential jet.

Font, G. I.↗

NASA NTRS1992

Image processing mini manual

The intent is to provide an introduction to the image processing capabilities available at the Langley Research Center (LaRC) Central Scientific Computing Complex (CSCC). Various image processing software components are described. Information is given concerning the use of these components in the Data Visualization and Animation Laboratory at LaRC.

Matthews, Christine G.↗

NASA NTRS1992

Experimental study of pylon geometries for transport aircraft

Pylon cross-sectional geometries that are intended to reduce propulsion system installation drag were investigated on a 1/17th-scale low-wing transport model in the NASA Langley 16-Foot Transonic Tunnel. The basic design philosophy for these pylons was to alleviate flow acceleration without introducing severe adverse pressure gradients near the pylon/wing junction. This was achieved by means of a gradually, diverging pylon with maximum thickness occurring at the wing trailing edge. The pylon closure occurs aft of the wing trailing edge. The force, surface pressure and surface flow visualization data obtained support this concept.

Naik, Dinesh A.↗

NASA NTRS1993

Global change information support: A north-south coalition

On a daily basis we become more aware that our planet, earth, exists in a delicate balance; we, its inhabitants, must be informed caretakers. Global change communities have emerged around the globe to address this multidisciplinary subject. Information systems that integrate text, bibliographic, numeric and visual data are needed to support these global change communities. No one information center can hope to collect all the relevant data. Rather, we must form a coalition, North and South, to collect and provide access to disparate, multidisciplinary sources of information, and to develop standardized tools for documenting and manipulating this data and information. International resources need to be mobilized in a coordinated manner to move us towards this goal. This paper looks at emerging information technologies that can be utilized to build such a system, and outlines some cooperative North/South strategies.

Blados, Walter R.↗

NASA NTRS1993

Neural networks for calibration tomography

Artificial neural networks are suitable for performing pattern-to-pattern calibrations. These calibrations are potentially useful for facilities operations in aeronautics, the control of optical alignment, and the like. Computed tomography is compared with neural net calibration tomography for estimating density from its x-ray transform. X-ray transforms are measured, for example, in diffuse-illumination, holographic interferometry of fluids. Computed tomography and neural net calibration tomography are shown to have comparable performance for a 10 degree viewing cone and 29 interferograms within that cone. The system of tomography discussed is proposed as a relevant test of neural networks and other parallel processors intended for using flow visualization data.

Decker, Arthur↗

NASA NTRS1993

The ground vortex flow field associated with a jet in a cross flow impinging on a ground plane for uniform and annular turbulent axisymmetric jets

An experimental study was conducted of the impingement of a single circular jet on a ground plane in a cross flow. This geometry is a simplified model of the interaction of propulsive jet exhaust from a V/STOL aircraft with the ground in forward flight. Jets were oriented normal to the cross flow and ground plane. Jet size, cross flow-to-jet velocity ratio, ground plane-to-jet board spacing, and jet exit turbulence level and mean velocity profile shape were all varied to determine their effects on the size of the ground vortex interaction region which forms on the ground plane, using smoke injection into the jet. Three component laser Doppler velocimeter measurements were made with a commercial three color system for the case of a uniform jet with exit spacing equal to 5.5 diameters and cross flow-to-jet velocity ratio equal to 0.11. The flow visualization data compared well for equivalent runs of the same nondimensional jet exit spacing and the same velocity ratio for different diameter nozzles, except at very low velocity ratios and for the larger nozzle, where tunnel blockage became significant. Variation of observed ground vortex size with cross flow-to-jet velocity ratio was consistent with previous studies. Observed effects of jet size and ground plane-to-jet board spacing were relatively small. Jet exit turbulence level effects were also small. However, an annular jet with a low velocity central core was found to have a significantly smaller ground vortex than an equivalent uniform jet at the same values of cross flow-to-jet velocity ratio and jet exit-to-ground plane spacing. This may suggest a means of altering ground vortex behavior somewhat, and points out the importance of proper simulation of jet exit velocity conditions. LV data indicated unsteady turbulence levels in the ground vortex in excess of 70 percent.

Cavage, William M.↗