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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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At least 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Transmission of sound in ducts with thin shear layers - Convergence to the uniform flow case.

The problem of the transmission of sound in a duct with very thin shear layers at the walls is treated by an inner expansion method. The results show that the formulation of the problem of the transmission of sound in a duct with a shear layer at the wall converges, in the case of a vanishingly thin shear layer, to the formulation of the same problem when uniform flow is assumed and the wall boundary condition is that of continuity of particle displacement.

Eversman, W.↗
NASA NTRS1973

Digital servo control of random sound fields

It is necessary to place number of sensors at different positions in sound field to determine actual sound intensities to which test object is subjected. It is possible to determine whether specification is being met adequately or exceeded. Since excitation is of random nature, signals are essentially coherent and it is impossible to obtain true average.

Nakich, R. B.↗
NASA NTRS1973

Emission of sound from turbulence convected by a parallel flow in the presence of solid boundaries

A theoretical description is given of the sound emitted from an arbitrary point in a parallel or nearly parallel turbulent shear flow confined to a region near solid boundaries. The analysis begins with Lighthill's formulation of aerodynamic noise and assumes that the turbulence is axisymmetric. Specific results are obtained for the sound emitted from an arbitrary point in a turbulent flow within a semi-infinite, open-ended duct.

Goldstein, M. E.↗
NASA NTRS1973

The circulation of Prince William Sound

The author has identified the following significant results. Results suggest that sediment-laden plumes of fresh water from rivers may be useful tracers, due to their high visibility, of surface water motion. The two useable images obtained to date corroborate that westerly flow was occurring in the Gulf of Alaska just south of Prince William Sound, and that an inflow into Prince William Sound was occurring concurrently with flood tides on both occasions. River plumes are useful tracers, but poor weather conditions somewhat limit the use of satellite imagery.

Muench, R. D.↗
NASA NTRS1973

Determination of the distribution of sound source intensities in subsonic and supersonic jets

Equations relating crossed beam space-time correlations to the sound source strength per unit length of an idealized jet are presented and applied to actual measurements in unheated jets at M = 0.71 and M = 1.0. The infrared crossed beam system was assembled and checked out. The prediction of the system's insensitivity to temperature fluctuations when set at 4.31 microns with a 0.08 micron bandpass was checked. Relative intensity profiles of density fluctuations for jets at M = 0.71, 1.0 and 1.94 were measured. These profiles differ considerably from velocity fluctuation profiles measured by other investigators with hotwires. The convection speeds also differ. Finally, the sound source strengths per unit length are obtained at various axial distances for the subsonic and sonic jet. The sonic jet shows peak source strength at an axial distance of six diameters.

Damkevala, R. J.↗
NASA NTRS1973

Investigation of the Statistics of Pure Tone Sound Power Injection from Low Frequency, Finite Sized Sources in a Reverberant Room

The effect of finite source size on the power statistics in a reverberant room for pure tone excitation was investigated. Theoretical results indicate that the standard deviation of low frequency, pure tone finite sources is always less than that predicted by point source theory and considerably less when the source dimension approaches one-half an acoustic wavelength or greater. A supporting experimental study was conducted utilizing an eight inch loudspeaker and a 30 inch loudspeaker at eleven source positions. The resulting standard deviation of sound power output of the smaller speaker is in excellent agreement with both the derived finite source theory and existing point source theory, if the theoretical data is adjusted to account for experimental incomplete spatial averaging. However, the standard deviation of sound power output of the larger speaker is measurably lower than point source theory indicates, but is in good agreement with the finite source theory.

Smith, Wayne Farrior↗
NASA NTRS1973

Plume development in Long Island Sound observed by remote sensing (ERTS-1)

As the Connecticut River flows into Long Island Sound, large plumes are developed during the mixing of ocean and estuarine waters. Plumes were delineated for July 28, October 8, October 27, and December 2, 1972, by analyzing ERTS-1 imagery with the SRI electronic satellite image analysis console (ESIAC). Insertion of MSS band 5 into the ESIAC produced the best result in this analysis. The four plumes that have been delineated provide the first input to a time-lapse analysis of circulation patterns at the eastern end of Long Island Sound.

Ruggles, F. H., Jr.↗
NASA NTRS1973

A model for the pressure excitation spectrum and acoustic impedance of sound absorbers in the presence of grazing flow

The acoustic impedance of sound absorbers in the presence of grazing flow is essential information when analyzing sound propagation within ducts. A unification of the theory of the nonlinear acoustic resistance of Helmholtz resonators including grazing flow is presented. The nonlinear resistance due to grazing flow is considered to be caused by an exciting pressure spectrum produced by the interaction of the grazing flow and the jets flowing from the resonator orifices. With this exciting pressure spectrum the resonator can be treated in the same manner as a resonator without grazing flow but with an exciting acoustic spectrum.

Rice, E. J.↗
NASA NTRS1973

The design and development of an automatic control system for the in-duct cancellation of spinning modes of sound

The reduction is discussed of the discrete tones generated by jet engines which is essential for jet aircraft to meet present and proposed noise standards. The discrete tones generated by the blades and vanes propagate in the inlet and exhaust duct in the form of spiraling acoustic waves, or spinning modes. The reduction of these spinning modes by the cancellation effect of the combination of two acoustic fields was investigated. The spinning mode synthesizer provided the means for effective study of this noise reduction scheme. Two sets of electrical-acoustical transducers located in an equally-spaced circular array simultaneously generate a specified spinning mode and the cancelling mode. Analysis of the wave equation for the synthesizer established the optimum cancelling array acoustic parameters for maximum sound pressure level reduction. The parameter dependence of the frequency ranges of propagation of single, specified circumferential modes generated by a single array, and of effective cancellation of the modes generated by two arrays, was determined. Substantial sound pressure level reduction was obtained for modes within these limits.

Harrington, W. W.↗
NASA NTRS1974

Transparent sound screens

Transparent sound screens consisting of glass (organic glass) plates placed at fixed angles with respect to the floor are considered. Noise levels in the screened area depend on the cumulative effect of direct, reverberated and refracted components of sound energy radiated by the source. This effect is analyzed on the analogy of the summation of electrical impedances. Inasmuch as under given circumstances sufficient noise control can be obtained, transparent screens seem to solve the problem of unimpeded supervision of installations in noisy workshops and power plants; in administrative buildings, computing centers, design bureaus, etc., they ensure acoustic comfort without space losses and without inspiring claustrophobia.

Bizo, F.↗
NASA NTRS1974

Concerning the sound insulation of building elements made up of light concretes

The sound insulating capacity of building elements made up of light concretes is considered. Analyzing differentially the behavior of light concrete building elements under the influence of incident acoustic energy and on the basis of experimental measurements, coefficients of correction are introduced into the basic formulas for calculating the sound insulating capacity for the 100-3,2000 Hz frequency band.

Giurgiu, I. I.↗
NASA NTRS1974

Highly efficient special sound absorbing solutions

Highly efficient special sound absorbing structures with the following criteria are considered: (1) A distribution surface of the sound absorbing material greater than that of the building element on which the structure is placed; (2) The highest possible absorption coefficient in the widest possible frequency band; and (3) adaptability to different construction and aesthetic conditions.

Ionescu, M.↗
NASA NTRS1974

Digital servo control of random sound test excitation

A digital servocontrol system for random noise excitation of a test object in a reverberant acoustic chamber employs a plurality of sensors spaced in the sound field to produce signals in separate channels which are decorrelated and averaged. The average signal is divided into a plurality of adjacent frequency bands cyclically sampled by a time division multiplex system, converted into digital form, and compared to a predetermined spectrum value stored in digital form. The results of the comparisons are used to control a time-shared up-down counter to develop gain control signals for the respective frequency bands in the spectrum of random sound energy picked up by the microphones.

Nakich, R. B.↗
NASA NTRS1974

Data for NASA's AVE 2 pilot experiment. Part 1: 25-mb sounding data and synoptic charts

Tabulated rawinsonde data at 25-mb intervals from surface to 25 mb is presented for the 54 stations participating in the Atmospheric Variability Experiment 11 pilot experiment which began at 12 GMT on May 11, 1974, and ended at 12 GMT on May 12, 1974. Soundings were made at 3 hour intervals. A brief discussion is included on methods of processing and data accuracy, and synoptic charts prepared from the the data are presented. The area covered by the sounding stations is the eastern United States, east of approximately 105 deg west longitude.

Scoggins, J. R.↗
NASA NTRS1973

Mississippi Sound remote sensing study

A study of the Mississippi Sound was initiated in early 1971 by personnel of NASA Earth Resources Laboratory. Four separate seasonal experiments consisting of quasi-synoptic remote and surface measurements over the entire area were planned. Approximately 80 stations distributed throughout Mississippi Sound were occupied. Surface water temperature and secchi extinction depth were measured at each station and water samples were collected for water quality analyses. The surface distribution of three water parameters of interest from a remote sensing standpoint - temperature, salinity and chlorophyll content - are displayed in map form. Areal variations in these parameters are related to tides and winds. A brief discussion of the general problem of radiative measurements of water temperature is followed by a comparison of remotely measured temperatures (PRT-5) to surface vessel measurements.

Atwell, B. H.↗
NASA NTRS1974

Remote temperature sounding in the presence of cloud by zenith scanning

The principles of remote sounding of vertical temperature profiles in planetary atmospheres containing cloud layers are presented for an approach that uses measurements at different angles to the local vertical to eliminate the unknown cloud effects. A numerical example for a model of the earth's atmosphere shows that soundings separated by 40 deg in zenith angle permit the recovery of the temperature profile with an error that is not significantly greater than that obtained in the clear atmosphere case, and without serious horizontal smear. It is proposed that the method will be valuable for the interpretation of measurements made by instruments on spin-stabilized spacecraft on planetary missions, since in these cases the required angular coverage is obtained automatically for most trajectories.

Taylor, F. W.↗
NASA NTRS1974

Effect of transverse velocity and temperature gradients on sound attenuation in two-dimensional ducts

An investigation is described of the effect of transverse mean-velocity and temperature gradients on sound attenuation in acoustically treated two-dimensional ducts. The results show that cooling the duct walls leads to channeling the sound toward the walls for both downstream and upstream propagation. The effect of mean-temperature gradients on the attenuation rates of the lowest three modes can be as important as the effect of mean-velocity gradients.

Nayfeh, A. H.↗
NASA NTRS1975

Sound separation probe

Probe separates sound waves from turbulent flow pressure fluctuations in ducted airstreams by using principle that sound waves and turbulent flow pressure perturbations travel at different velocities.

Moore, M. T.↗