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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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14 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1956

Contributions on the mechanics of boundary-layer transition

The manner in which flow in a boundary layer becomes turbulent was investigated on a flat plate at wind speeds generally below 100 feet per second. Hot-wire techniques were used, and many of the results are derived from oscillograms of velocity fluctuations in the transition region. Following a presentation of the more familiar aspects of transition, there are presented the very revealing facts discovered while studying the characteristics of artificially produced turbulent spots. These are: (1) oscillograms of natural transition are identical to oscillograms of spot passage; (2) transition starts from perturbations in the laminar flow as spots which then grow in accordance with the general concept proposed by Emmons. (3) Turbulence always moves downstream followed by laminar flow; (4) the following flow is in a state of calm for a period during which transition will not occur.

Schubauer, G B↗
NASA NTRS1933

Pressure Rise, Gas Vibrations and Combustion Noises During the Explosion of Fuels

In the use of piezo-quartz indicators for high-speed automobile engines, the interpretation of pressure-time diagrams made by an oscillograph offers certain difficulties. On the one hand, the scale of the pressure amplitudes is not always the same under all conditions, while, on the other hand, the atmospheric zero line may be shifted from its correct position in the oscillogram. These facts make necessary to verify the readings of the quartz indicators by direct calibration before and after each series of tests and, on the basis of the results, to determine the scale for the oscillograms.

Wawrziniok,↗
NASA NTRS1974

Application of wave mechanics theory to fluid dynamics problems: Flat plate flow

The characteristics of the flow in the laminar boundary layer along an infinitely long flat plate are discussed. The flow may be disturbed or not, depending on the situation. The physical, natural aspects of the flow, either a laminar flow free from disturbances or a flow which originally is a laminar one with disturbances superimposed upon it. Oscillograms of turbulence in wind tunnel tests and in the wake of a cylinder are presented.

Krzywoblocki, M. Z. V.↗
NASA NTRS1974

Relationships among classes of self-oscillating transistor parallel inverters

A procedure is developed for classifying dc-to-square-wave two-transistor parallel inverters used in power conditioning applications. The inverters are reduced to equivalent RLC networks and are then grouped with other inverters with the same basic equivalent circuit. Distinction between inverter classes is based on the topology characteristics of the equivalent circuits. Information about one class can then be extended to another class using the basic oscillation theory and the concept of duality. Oscillograms from test circuits confirm the validity of the procedure adopted.

Wilson, T. G.↗
NASA NTRS1976

Magnetostrictive ultrasonic probes

The principles underlying the design and use of magnetostrictive ultrasonic probes is illustrated by oscillograms and sketches. Attention is given to such concepts as magnetostrictive transduction, broadband pulse shaping, guided wave propagation, wave impedance, reflection, transmission, and attenuation coefficients, coupling methods, and impulse-induced resonance. A number of applications of such probes are discussed including the measurement of elastic moduli, temperature, and acoustic emission and resonance studies.

Lynnworth, L. C.↗
NASA NTRS1977

Basic results of the medical research conducted during the flight of two crews on the Salyut-5 orbital station

The study of the effect of space factors, especially weightlessness, on man, taking into account prophylactic measures and devices to counteract that effect was part of the program for two flights on the Salyut 5 orbital station. Information from the equipment on board was transmitted telemetrically including: an electrocardiogram; a sphygmogram of carotid and femoral arteries; a kinetocardiogram; a tacho-oscillogram of the humeral artery, perimetric oscillations of the femur, venous pulse and pressure in the jugular veins, vital capacity of the lungs, respiration rate and lung ventilation. Stress factors, metabolism, biological and bacteriological and other tests were included. A comparison was made between these data and pre- and postflight test result.

Source record↗
NASA NTRS1978

Measurements of kinetic processes in a self-sustained discharge XeF laser

Measurements are presented for processes occurring in XeF self-sustained discharges including fluorescence, gain, and absorption at different wavelengths as a function of F2, Xe, and He partial pressures. Time-correlated oscillograms are given for the laser discharge current, metastable XeF small-signal gain at 351.1 nm, transient absorptions at 333.6 and 363.8 nm, metastable-XeF B-state sidelight emission at about 350 nm, metastable-F emission at 634.8 nm, and metastable-F emission at 731.1 nm. It is found that He atoms are necessary for the production of metastable-XeF in its lower vibrational levels and that radiative processes and He quenching are the primary mechanisms for metastable-XeF decay. For small-signal gains of as low as about 8%/cm, the transient absorption at the laser wavelength may be as large as about 1-2%/cm.

Gower, M. C.↗
NASA NTRS1982

Development of an automated processing and screening system for the space shuttle orbiter flight test data

One nemesis of the structural dynamist is the tedious task of reviewing large quantities of data. This data, obtained from various types of instrumentation, may be represented by oscillogram records, root-mean-squared (rms) time histories, power spectral densities, shock spectra, 1/3 octave band analyses, and various statistical distributions. In an attempt to reduce the laborious task of manually reviewing all of the space shuttle orbiter wideband frequency-modulated (FM) analog data, an automated processing system was developed to perform the screening process based upon predefined or predicted threshold criteria.

Mccutchen, D. K.↗
NASA NTRS1983

Flow mechanism and experimental investigation of a rotating stall in transonic compressors

The flow characteristics of the rotating stall in compressors is studied, and a flow model is developed along with a theoretical calculation method based on vortex theory. A detailed theoretical calculation is completed for a two dimensional flow field in a transonic rotor in a rotating stall, and the result is in good agreement with experimental findings. The oscillograms of time-varying stall characteristic parameters recorded for the onset, growth, and cessation processes of rotating stall are analyzed, and some new flow phenomena deserving of further investigation are discovered. These include serious separation of individual blades, often preceding the onset of rotating stall in compressors with very small blade-camber angles, and periodical variation of the circumferential width of the stall cell with time, accompanied by periodical oscillation of the width of the stall cell in the radial direction of the blade. The circumferential and radial oscillation frequencies are the same.

Yajun, L.↗
NASA NTRS1989

Analytical and experimental study of high phase order induction motors

Induction motors having more than three phases were investigated to determine their suitability for electric vehicle applications. The objective was to have a motor with a current rating lower than that of a three-phase motor. The name chosen for these is high phase order (HPO) motors. Motors having six phases and nine phases were given the most attention. It was found that HPO motors are quite suitable for electric vehicles, and for many other applications as well. They have characteristics which are as good as or better than three-phase motors for practically all applications where polyphase induction motors are appropriate. Some of the analysis methods are presented, and several of the equivalent circuits which facilitate the determination of harmonic currents and losses, or currents with unbalanced sources, are included. The sometimes large stator currents due to harmonics in the source voltages are pointed out. Filters which can limit these currents were developed. An analysis and description of these filters is included. Experimental results which confirm and illustrate much of the theory are also included. These include locked rotor test results and full-load performance with an open phase. Also shown are oscillograms which display the reduction in harmonic currents when a filter is used with the experimental motor supplied by a non-sinusoidal source.

Klingshirn, Eugene A.↗
NASA NTRS1937

Valve-spring Surge

Test equipment is described that includes a system of three quartz indicators whereby three different pressures could be synchronized and simultaneously recorded on a single oscillogram. This equipment was used to test the reliction of waves at ends of valve spring, the dynamical stress of the valve spring for a single lift of the valve, and measurement of the curve of the cam tested. Other tests included simultaneous recording of the stress at both ends of the spring, spring oscillation during a single lift as a function of speed, computation of amplitude of oscillation for a single lift by harmonic analysis, effect of cam profile, the setting up of resonance, and forced spring oscillation with damping.

Marti, Willy↗
NASA NTRS1936

Ignition and Flame Development in the Case of Diesel Fuel Injection

To investigate the process of ignition and combustion in the case of spray injection into heated air, a new form of apparatus is developed and the tests carried out with it described. Photographs of the spray before and after ignition are obtained at frequencies of 500 pictures per second. Pressures and temperatures are simultaneously recorded on oscillograms. Information on the initial conditions, ignition time lag, period of complete combustion, place where ignition starts, and general course of the combustion is obtained.

Holfelder, Otto↗