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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Measurement of acoustic shielding by a turbulent jet

The acoustic shielding properties of a turbulent jet have been investigated experimentally. The experimental arrangement consisted of an acoustic point source and a turbulent shielding jet. The source and jet parameters investigated include the source frequency, source spectrum, jet velocity, jet heating by simulation and the lateral and longitudinal source positions with respect to the shielding jet. It is found that the maximum sound attenuation provided by the shielding jet depends on the balance between refraction and diffraction. Over the frequency range investigated, the redistribution of sound by the shielding air jet is power conserving. Comparison between measurement and prediction based on an idealized cylindrical uniform jet model indicates that the spreading and decay of the flow field in real jets are important. Comparisons between the present data trends and those reported for jet-by-jet shielding suggest that the major effects observed in the latter are acoustical rather than aerodynamical.

Yu, J. C.↗
NASA NTRSDate not supplied

Asteroseismic Inversions of Mixed Acoustic-Gravity Modes to Probe the Stellar Core Structure

The discovery of mixed acoustic-gravity modes of oscillations of moderate mass stars opens a unique opportunity to infer the structure of the inner energy-generating cores and thus test the stellar evolution theory. The mixed modes have properties of internal gravity waves (g-modes) in the convectively stable helium core and properties of acoustic modes outside the core. We select several sets of the oscillation mode frequencies in the mass range from about 1.3 to 1.6 solar masses from the Kepler Legacy database, and apply the optimally localized averaging inversion technique previously developed for low-degree helioseismology. The inversion technique takes into account the uncertainties in the determination of the mass and radius of the stars, as well as the surface effects. The methodology provides sensitivity kernels for various structure properties, including the sound speed, density, and Ledoux parameter of convective stability, and, thus, the direct relationship between the stellar properties and the deviation of observed frequencies from the reference models. The inversion results reveal significant deviations in the core structure from the reference models calculated using the MESA evolutionary code for the stellar parameters obtained by the asteroseismic model grid fitting. Our analysis shows that the best resolution of the inner helium core and surrounding shell is achieved in inversions for the Ledoux parameter.

SMD↗
NASA NTRS1977

A research to reduce interior noise in general aviation airplanes. General aviation interior noise study

The construction, calibration, and properties of a facility for measuring sound transmission through aircraft type panels are described along with the theoretical and empirical methods used. Topics discussed include typical noise source, sound transmission path, and acoustic cabin properties and their effect on interior noise. Experimental results show an average sound transmission loss in the mass controlled frequency region comparable to theoretical predictions. The results also verify that transmission losses in the stiffness controlled region directly depend on the fundamental frequency of the panel. Experimental and theoretical results indicate that increases in this frequency, and consequently in transmission loss, can be achieved by applying pressure differentials across the specimen.

Roskam, J.↗
NASA NTRS1990

Particle Cloud Flames in Acoustic Fields

Results are presented on a study of flames supported by clouds of particles suspended in air, at pressures about 100 times lower than normal. In the experiment, an acoustic driver (4-in speaker) placed at one end of a closed tube, 0.75-m long and 0.05 m in diameter, disperses a cloud of lycopodium particles during a 0.5-sec powerful acoustic burst. Properties of the particle cloud and the flame were recorded by high-speed motion pictures and optical transmission detectors. Novel flame structures were observed, which owe their features to partial confinement, which encourages flame-acoustic interactions, segregation of particle clouds into laminae, and penetration of the flame's radiative flux density into the unburned particle-cloud regimes. Results of these experiments imply that, for particles in confined spaces, uncontrolled fire and explosion may be a threat even if the Phi(0) values are below some apparent lean limit.

Berlad, A. L.↗
NASA NTRS1974

Transmission of sound through annular ducts of varying cross sections and sheared mean flow

An asymptotic solution is presented for the transmission and attenuation of acoustic waves in an annular duct of slowly varying cross section which carries a sheared mean flow. The analysis also takes into account the growth of the boundary layer as well as any slow variations in the acoustic liner properties. The problem is reduced to the solution of a first-order ordinary differential equation for the amplitude. The analysis is used to estimate the effects of the variations of the duct cross section and boundary layer growth on the different acoustic modes.

Nayfeh, A. H.↗
NASA NTRSDate not supplied

Validation of Noise Propagation for Lined Inlets

Commercial finite element modeling tools are validated for use on inlet radiated noise predictions for an acoustically lined subsonic aircraft inlet tested in the NASA Glenn 9-foot by 15-foot low-speed wind tunnel. An in-depth review and prediction of the acoustic liner properties on the Advanced Ducted Propulsor were conducted for use in the noise predictions. Agreement between the inlet radiated noise predictions to the measured tones at approach was used as the validation for the prediction tools. Similar follow-up predictions were conducted for an acoustically lined supersonic inlet. A follow-up investigation on the effect of the acoustic liner placement within the supersonic inlet was undertaken.

Acoustics↗
NASA NTRS1996

Flight and Static Exhaust Flow Properties of an F110-GE-129 Engine in an F-16XL Airplane During Acoustic Tests

The exhaust flow properties (mass flow, pressure, temperature, velocity, and Mach number) of the F110-GE-129 engine in an F-16XL airplane were determined from a series of flight tests flown at NASA Dryden Flight Research Center, Edwards, California. These tests were performed in conjunction with NASA Langley Research Center, Hampton, Virginia (LARC) as part of a study to investigate the acoustic characteristics of jet engines operating at high nozzle pressure conditions. The range of interest for both objectives was from Mach 0.3 to Mach 0.9. NASA Dryden flew the airplane and acquired and analyzed the engine data to determine the exhaust characteristics. NASA Langley collected the flyover acoustic measurements and correlated these results with their current predictive codes. This paper describes the airplane, tests, and methods used to determine the exhaust flow properties and presents the exhaust flow properties. No acoustics results are presented.

Holzman, Jon K.↗
NASA NTRS1995

Neural Network Burst Pressure Prediction in Graphite/Epoxy Pressure Vessels from Acoustic Emission Amplitude Data

Acoustic emission (AE) data were taken during hydroproof for three sets of ASTM standard 5.75 inch diameter filament wound graphite/epoxy bottles. All three sets of bottles had the same design and were wound from the same graphite fiber; the only difference was in the epoxies used. Two of the epoxies had similar mechanical properties, and because the acoustic properties of materials are a function of their stiffnesses, it was thought that the AE data from the two sets might also be similar; however, this was not the case. Therefore, the three resin types were categorized using dummy variables, which allowed the prediction of burst pressures all three sets of bottles using a single neural network. Three bottles from each set were used to train the network. The resin category, the AE amplitude distribution data taken up to 25 % of the expected burst pressure, and the actual burst pressures were used as inputs. Architecturally, the network consisted of a forty-three neuron input layer (a single categorical variable defining the resin type plus forty-two continuous variables for the AE amplitude frequencies), a fifteen neuron hidden layer for mapping, and a single output neuron for burst pressure prediction. The network trained on all three bottle sets was able to predict burst pressures in the remaining bottles with a worst case error of + 6.59%, slightly greater than the desired goal of + 5%. This larger than desired error was due to poor resolution in the amplitude data for the third bottle set. When the third set of bottles was eliminated from consideration, only four hidden layer neurons were necessary to generate a worst case prediction error of - 3.43%, well within the desired goal.

Hill, Eric v. K.↗
NASA NTRS2002

Effects of Liner Geometry on Acoustic Impedance

Current aircraft engine nacelles typically contain acoustic liners consisting of perforated sheets bonded onto honeycomb cavities. Numerous models have been developed to predict the acoustic impedance of these liners in the presence of grazing flow, and to use that information with aeroacoustic propagation codes to assess nacelle liner noise suppression. Recent efforts have provided advances in impedance education methodologies that offer more accurate determinations of acoustic liner properties in the presence of grazing flow. The current report provides the results of a parametric study, in which a finite element method was used to assess the effects of variations of the following geometric parameters on liner impedance, with and without the presence of grazing flow: percent open area, sheet thickness, sheet thickness-to-hole diameter ratio and cavity depth. Normal incidence acoustic impedances were determined for eight acoustic liners, consisting of punched aluminum facesheets bonded to hexcell honeycomb cavities. Similar liners were tested in the NASA Langley Research Center grazing incidence tube to determine their response in the presence of grazing flow. The resultant data provide a quantitative assessment of the effects of these perforate, single-layer liner parameters on the acoustic impedance of the liner.

Jones, Michael G.↗
NASA NTRS1984

Acoustic Design Improves Composite Impact Resistance

Improved tolerance of composites to impact damage achieved using acoustic response model to characterize dynamics of damage mechanism. Model based on assumption that in addition to classical mechanical properties, damage mechanism depends on acoustic properties of composite material. Use of model results in more-impact-resistant composite structure.

Heyman, J. S.↗
NASA NTRS1973

An improved method for design of expansion-chamber mufflers with application to an operational helicopter

An improved method for the design of expansion-chamber mufflers is described and applied to the task of reducing exhaust noise generated by a helicopter. The method is an improvement of standard transmission-line theory in that it accounts for the effect of the mean exhaust-gas flow on the acoustic-transmission properties of a muffler system, including the termination boundary condition. The method has been computerized, and the computer program includes an optimization procedure that adjusts muffler component lengths to achieve a minimum specified desired transmission loss over a specified frequency range. A printout of the program is included together with a user-oriented description.

Parrott, T. L.↗
NASA NTRS1974

Influence of acoustic parameters on the mechanical properties of low-alloy steels welded in a vibrated field

The advantages and disadvantages of slag welding are given. A suitable method is proposed for introducing ultrasonic oscillations in the process of depositing the metal in the slag bath. Some practical results are given of experimental studies of the mechanical and structural characteristics obtained with the welding of steels under vibrated and nonvibrated conditions, respectively. Certain physical phenomena that attend the moving metal particle in slag welding are analyzed.

Sonea, I.↗
NASA NTRS1976

One-dimensional wave propagation in particulate suspensions

One-dimensional small-amplitude wave motion in a two-phase system consisting of an inviscid gas and a cloud of suspended particles is analyzed using a continuum theory of suspensions. Laplace transform methods are used to obtain several approximate solutions. Properties of acoustic wave motion in particulate suspensions are inferred from these solutions.

Rochelle, S. G.↗
NASA NTRS1976

Optimal one-section and two-section circular sound-absorbing duct liners for plane-wave and monopole sources without flow

A discrete frequency study is made of the influence of source characteristics on the optimal properties of acoustically lined uniform and two section ducts. Two simplified sources, a plane wave and a monopole, are considered in some detail and over a greater frequency range than has been previously studied. Source and termination impedance effects are given limited examination. An example of a turbomachinery source and three associated source variants is also presented. Optimal liner designs based on modal theory approach the Cremer criterion at low frequencies and the geometric acoustics limit at high frequencies. Over an intermediate frequency range, optimal two section liners produced higher transmission losses than did the uniform configurations. Source distribution effects were found to have a significant effect on optimal liner design, but source and termination impedance effects appear to be relatively unimportant.

Lester, H. C.↗
NASA NTRS1981

A study of poultry processing plant noise control techniques

A number of techniques can be used to reduce noise in poultry processing plants. In general, covering the ceiling with a noise-absorbing medium is a practical first step. Once the reflected noise levels are abated, treatment of specific identifiable noise courses can take place. The development, flammability, and mechanical properties of acoustic panels to be vertically suspended from the ceiling are discussed as well as the covers need to comply with USDA cleanability requirements. The isolation of drive motors and pumps from large expansive areas, the muffling of pneumatic devices, and the insulation of ice chutes are methods of source quieting. Proper maintenance of machinery and vibration monitoring are also needed to reduce hearing damage risk and to improve worker productivity and employee/supervisor relations.

Wyvill, J. C.↗
NASA NTRS1981

Measurements of He D3 profiles in solar plages

Measurements of the profiles of the He D3 lines in solar plages are presented as a probe of the plage atmosphere. Observations were made at selected positions in quiescent plages during the period October 1978-April 1979 by the 25-cm coronagraph/3-m coude spectrograph at the Mees Solar Observatory on Mount Haleakala. Individual D3 plage profiles are fit well with a two-component, differentially moving atmosphere with constant source function and total Doppler width. The principal absorption is attributed to nearly stationary material, with a kinetic temperature less than 17,200 K, and velocity distribution is found to represent a net downflow in the plage atmosphere extending to around 12 km/sec. The present results for individual plage profiles are also noted to be consistent with those of Namba (1963). Time series of D3 profiles at fixed plage positions and the velocity spectra for nearby photospheric lines are observed to show general enhancements at periods of around 5 min, with redshift leading variations in line width by about 49 deg. Interpretations of the width variation as temperature variations are found not to be consistent with the properties of acoustic wave modes in a stratified atmosphere, presumably indicating magnetic field effects.

Landman, D. A.↗
NASA NTRS1983

Surface acoustic admittance of highly porous open-cell, elastic foams

This work presents a comprehensive study of the surface acoustic admittance properties of graded sizes of open-cell foams that are highly porous and elastic. The intrinsic admittance as well as properties of samples of finite depth were predicted and then measured for sound at normal incidence over a frequency range extending from about 35-3500 Hz. The agreement between theory and experiment for a range of mean pore size and volume porosity is excellent. The implications of fibrous structure on the admittance of open-cell foams is quite evident from the results.

Lambert, R. F.↗