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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1971

Jet-noise reduction through liquid-base foam injection.

An experimental investigation has been made of the sound-absorbing properties of liquid-base foams and of their ability to reduce jet noise. Protein, detergent, and polymer foaming agents were used in water solutions. A method of foam generation was developed to permit systematic variation of the foam density. The investigation included measurements of sound-absorption coefficents for both plane normal incidence waves and diffuse sound fields. The intrinsic acoustic properties of foam, e.g., the characteristic impedance and the propagation constant, were also determined. The sound emitted by a 1-in.-diam cold nitrogen jet was measured for subsonic (300 m/sec) and supersonic (422 m/sec) jets, with and without foam injection. Noise reductions up to 10 PNdB were measured.

Manson, L.↗
NASA NTRS1975

On the excess attenuation of sound in the atmosphere

The attenuation suffered by an acoustic plane wave propagating from an elevated source to the ground, in excess of absorption losses, was studied. Reported discrepancies between attenuation measurements made in the field and theories which only account for absorption losses are discussed. It was concluded that the scattering of sound by turbulence results in a nonnegligible contribution to the total attenuation.

Deloach, R.↗
NASA NTRS1977

Adiabatic pressure dependence of the 2.7 and 1.9 micron water vapor bands

An acoustic excitation technique is used to determine the adiabatic pressure derivative of the spectral absorptance of the 2.7 and 1.9 micron water vapor bands, and the 3.5 micron HCl band. The dependence of this derivative on thermodynamic parameters such as temperature, concentration, and pressure is evaluated. A cross-flow water vapor system is used to measure spectral absorptance. Taking F as the ratio of nonrigid to rotor line strengths, it is found that an F factor correction is needed for the 2.7 micron band. The F factor for the 1.9 micron band is also determined. In the wings of each band a wavelength can be found where the concentration dependence is predominant. Farther out in the wings a local maximum occurs for the temperature derivative. It is suggested that the pressure derivative is significant in the core of the band.

Mathai, C. V.↗
NASA NTRS1983

Characteristics of the transmission loss apparatus at NASA Langley Research Center

A description of the Transmission Loss Apparatus at NASA Langley Research Center, which is specifically designed to accommodate general aviation type aircraft structures, is presented. The measurement methodology, referred to as the Plate Reference Method, is discussed and compared with the classical method as described in the Standard of the American Society for Testing and Materials. This measurement procedure enables reliable and accurate noise transmission loss measurements down to the 50 Hz one-third octave band. The transmission loss characteristics of add-on acoustical treatments, applied to the basic structure, can be established by inclusion of appropriate absorption corrections for the treatment.

Grosveld, F. W.↗
NASA NTRS1986

Consideration of some factors affecting low-frequency fuselage noise transmission for propeller aircraft

Possible reasons for disagreement between measured and predicted trends of sidewall noise transmission at low frequency are investigated using simplified analysis methods. An analytical model combining incident plane acoustic waves with an infinite flat panel is used to study the effects of sound incidence angle, plate structural properties, frequency, absorption, and the difference between noise reduction and transmission loss. Analysis shows that these factors have significant effects on noise transmission but they do not account for the differences between measured and predicted trends at low frequencies. An analytical model combining an infinite flat plate with a normally incident acoustic wave having exponentially decaying magnitude along one coordinate is used to study the effect of a localized source distribution such as is associated with propeller noise. Results show that the localization brings the predicted low-frequency trend of noise transmission into better agreement with measured propeller results. This effect is independent of low-frequency stiffness effects that have been previously reported to be associated with boundary conditions.

Mixson, J. S.↗
NASA NTRS1987

Jovian seismology

It is hypothesized that observations of the Doppler shifting of IR and UV absorption lines may furnish a powerful method for the detection of 4.5-9 min standing acoustic waves trapped in a wave duct beneath the Jupiter tropopause. Similarly, data could be obtained on Jupiter's thermal and density structure, and on the depth to which its zonal winds penetrate. The present model of standing oscillations in the molecular hydrogen envelope gives attention to theoretical eigenfrequencies and to such forcing functions for wave generation as coupling with turbulent and convective motions, thermal instability due to radiative transfer, wave propagation effects in a saturated atmosphere, and ortho-to-parahydrogen conversion. The small contribution that the forcing mechanisms make to velocity amplitudes implies that the Doppler shifting caused by the waves may only be resolvable through the superposition of oscillation records to enhance S/N ratios.

Bercovici, D.↗
NASA NTRS1990

Models of space averaged energetics of plates

The analysis of high frequency vibrations in plates is of particular interest in the study of structure borne noise in aircrafts. The current methods of analysis are either too expensive (finite element method) or may have a confidence band wider than desirable (Statistical Energy Analysis). An alternative technique to model the space and time averaged response of structural acoustics problems with enough detail to include all significant mechanisms of energy generation, transmission, and absorption is highly desirable. The focus of this paper is the development of a set of equations which govern the space and time averaged energy density in plates. To solve this equation, a new type of boundary value problem must be treated in terms of energy density variables using energy and intensity boundary conditions. A computer simulation verification study of the energy governing equation is performed. A finite element formulation of the new equations is also implemented and several test cases are analyzed and compared to analytical solutions.

Bouthier, O. M.↗
NASA NTRS1982

Oblique incidence sound absorption of porous materials covered by perforated metal and exposed to tangential airflow

The purpose of this study was to evaluate several acoustic linings that are candidate designs for the Ames 40- by 80-Foot Wind Tunnel test section. The acoustic treatment will be used to reduce wall reflections from aircraft model noise sources. The goal is not simply to attenuate sound propagating down the duct, but rather to create a semi-anechoic space in a windy environment by absorbing at least 80% of the incident acoustic energy over a wide frequency range, if possible.

Soderman, Paul T.↗
NASA NTRS1982

A photophonic instrument concept to measure atmospheric aerosol absorption

A laboratory model of an instrument to measure the absorption of atmospheric aerosols was designed, built, and tested. The design was based on the photophonic phenomenon discovered by Bell and an acoustic resonator developed by Helmholtz. Experiments were done to show ways the signal amplitude could be improved and the noise reduced and to confirm the instrument was sensitive enough to be practical. The research was undertaken to develop concepts which show promise of being improvements on the instruments that are presently used to measure the absorption of the Sun's radiation by the Earth's atmospheric aerosols.

Engle, C. D.↗
NASA NTRS2001

Acoustical Testing Laboratory Developed to Support the Low-Noise Design of Microgravity Space Flight Hardware

The NASA John H. Glenn Research Center at Lewis Field has designed and constructed an Acoustical Testing Laboratory to support the low-noise design of microgravity space flight hardware. This new laboratory will provide acoustic emissions testing and noise control services for a variety of customers, particularly for microgravity space flight hardware that must meet International Space Station limits on noise emissions. These limits have been imposed by the space station to support hearing conservation, speech communication, and safety goals as well as to prevent noise-induced vibrations that could impact microgravity research data. The Acoustical Testing Laboratory consists of a 23 by 27 by 20 ft (height) convertible hemi/anechoic chamber and separate sound-attenuating test support enclosure. Absorptive 34-in. fiberglass wedges in the test chamber provide an anechoic environment down to 100 Hz. A spring-isolated floor system affords vibration isolation above 3 Hz. These criteria, along with very low design background levels, will enable the acquisition of accurate and repeatable acoustical measurements on test articles, up to a full space station rack in size, that produce very little noise. Removable floor wedges will allow the test chamber to operate in either a hemi/anechoic or anechoic configuration, depending on the size of the test article and the specific test being conducted. The test support enclosure functions as a control room during normal operations but, alternatively, may be used as a noise-control enclosure for test articles that require the operation of noise-generating test support equipment.

Cooper, Beth A.↗
NASA NTRS2014

Recent Improvements to the Acoustical Testing Laboratory at the NASA Glenn Research Center

The Acoustical Testing Laboratory (ATL) consists of a 27- by 23- by 20-ft (height) convertible hemi/anechoic chamber and separate sound-attenuating test support enclosure. Absorptive fiberglass wedges in the test chamber provide an anechoic environment down to 100 Hz. A spring-isolated floor system affords vibration isolation above 3 Hz. These specifications, along with very low design background levels, enable the acquisition of accurate and repeatable acoustical measurements on test articles that produce very low sound pressures. Removable floor wedges allow the test chamber to operate in either a hemi-anechoic or anechoic configuration, depending on the size of the test article and the specific test being conducted. The test support enclosure functions as a control room during normal operations. Recently improvements were accomplished in support of continued usage of the ATL by NASA programs including an analysis of the ultra-sonic characteristics. A 3-D traverse system inside the chamber was utilized for acquiring acoustic data for these tests. The traverse system drives a linear array of 13, 1/4 in.-microphones spaced 3 in. apart (36 in. span). An updated data acquisition system was also incorporated into the facility.

Podboy, Devin M.↗
NASA NTRS2014

Recent Improvements to the Acoustical Testing Laboratory at the NASA Glenn Research Center

The Acoustical Testing Laboratory (ATL) consists of a 27 by 23 by 20 ft (height) convertible hemi/anechoic chamber and separate sound-attenuating test support enclosure. Absorptive fiberglass wedges in the test chamber provide an anechoic environment down to 100 Hz. A spring-isolated floor system affords vibration isolation above 3 Hz. These specifications, along with very low design background levels, enable the acquisition of accurate and repeatable acoustical measurements on test articles that produce very low sound pressures. Removable floor wedges allow the test chamber to operate in either a hemi-anechoic or anechoic configuration, depending on the size of the test article and the specific test being conducted. The test support enclosure functions as a control room during normal operations. Recently improvements were accomplished in support of continued usage of the ATL by NASA programs including an analysis of the ultra-sonic characteristics. A 3 dimensional traverse system inside the chamber was utilized for acquiring acoustic data for these tests. The traverse system drives a linear array of 13, 1/4"-microphones spaced 3" apart (36" span). An updated data acquisition system was also incorporated into the facility.

Podboy, Devin M.↗
NASA NTRS1987

Effects of fiber motion on the acoustic behavior of an anisotropic, flexible fibrous material

The acoustic behavior of a flexible fibrous material was studied experimentally. The material consisted of cylindrically shaped fibers arranged in a batting with the fibers primarily aligned parallel to the face of the batting. This type of material was considered anisotropic, with the acoustic propagation constant depending on whether the dirction of sound propagation was parallel or normal to the fiber arrangement. Normal incidence sound absorption measurements were taken for both fiber orientations over the frequency range 140 to 1500 Hz and with bulk densities ranging from 4.6 to 67 kg/cu m. When the sound propagated in a direction normal to the fiber alignment, the measured sound absorption showed the occurrence of a strong resonance, which increased absorption above that attributed to viscous and thermal effects. When the sound propagated in a direction parallel to the fiber alignment, indications of strong resonances in the data were not present. The resonance in the data for fibers normal to the direction of sound propagation is attributed to fiber motion. An analytical model was developed for the acoustic behavior of the material displaying the same fiber motion characteristics shown in the measurements.

Dahl, Milo D.↗
NASA NTRS1990

Effects of fiber motion on the acoustic behavior of an anisotropic, flexible fibrous material

The acoustic behavior of a flexible fibrous material was studied experimentally. The material consisted of cylindrically shaped fibers arranged in a batting with the fibers primarily aligned parallel to the face of the batting. This type of material was considered anisotropic, with the acoustic propagation constant depending on whether the direction of sound propagation was parallel or normal to the fiber arrangement. Normal incidence sound absorption measurements were taken for both fiber orientations over the frequency range 140 to 1500 Hz and with bulk densities ranging from 4.6 to 67 kg/cu m. When the sound propagated in a direction normal to the fiber alignment, the measured sound absorption showed the occurrence of a strong resonance, which increased absorption above that attributed to viscous and thermal effects. When the sound propagated in a direction parallel to the fiber alignment, indications of strong resonances in the data were not present. The resonance in the data for fibers normal to the direction of sound propagation is attributed to fiber motion. An analytical model was developed for the acoustic behavior of the material displaying the same fiber motion characteristics shown in the measurements.

Dahl, Milo D.↗
NASA NTRS2000

High Amplitude Acoustic Behavior of a Slit-Orifice Backed by a Cavity

The objective of the study reported here was to acquire detailed acoustic data and limited and flow visualization data for numerical validation a new model of sound absorption by a very narrow rectangular slit backed by a cavity. The sound absorption model is being developed by Dr. C. K. W. Tam of Florida State University. This report documents normal incidence impedance measurements of a singular rectangular slit orifice with no mean flow. All impedance measurements are made within a 1.12 inch (28.5 mm) diameter impedance tube using the two-microphone method for several frequencies in the range 1000-6000Hz and incident sound pressure levels in the range 130 - 150 dB. In the interest of leaving the analysis of the data to the developers of more advanced analytical and computational models of sound absorption by narrow slits, we have refrained from giving our own explanations of the observed results, although many of the observed results can be explained using the classical explanations of sound absorption by orifices.

Ahuja, K. K.↗
NASA NTRS2000

High Amplitude Acoustic Behavior of a Slit-Orifice Backed by a Cavity

The objective of this study was to acquire detailed acoustic data and limited flow visualization data for numerical validation of a new model of sound absorption by a very narrow rectangular slit backed by a cavity. The sound absorption model is that being developed by Dr. C. K. W. Tam of Florida State University. This report documents normal incidence impedance measurements of a singular rectangular slit orifice with no mean flow. All impedance measurements are made within a 1.12 inch (28.5 mm) diameter impedance tube using the two-microphone method for several frequencies in the range 1000 - 6000Hz and incident sound pressure levels in the range 130 - 150 dB. In the interest of leaving the analysis of the data to the developers of more advanced Analytical and computational models of sound absorption by narrow slits, we authors have refrained from giving our own explanations of the observed results, although many of the observed results can be explained using the classical understanding of sound absorption by orifices.

Ahuja, K. K.↗
NASA NTRSDate not supplied

Final Master's Project Advised by Jiri Tichy on Architectural Acoustics

Jiri Tichy's interest and expertise in architectural acoustics research led to the formulation of a Master’s student project on the irregularity of low-frequency response in small rooms. The numerical study conducted under the guidance of Dr. Tichy by the present author addressed how to decrease the low-frequency sound field variability using a loudspeaker source with constant sound power radiation. A summary of the research results will be presented in terms of standard deviation, as a function of source position, receiver position, and room absorption. In addition, the presentation will include how this research experience instilled in the author a desire to continue pursuing acoustics research.

acoustics↗
NASA NTRSDate not supplied

Evaluation of Variable-Depth Liners with Slotted Cores

An initial evaluation of variable-depth, slotted-core liners fabricated with conventional, flightworthy components is presented. Liners with two distinct chamber lengths provide significant broadband absorption and their impedances are, to first order, predictable with the NASA impedance prediction code. These liners employ film caps embedded in alternating chambers to provide a near-rigid boundary condition. This enables improved control of the liner design process. A number of additively-manufactured, bent-chamber liners are also investigated to explore the effects of the bend on the liner impedance. The liner impedance is negligibly affected by changes to the partition width, but is significantly affected by changes to the slot height. This offers an option for achieving low-frequency sound absorption with relatively thin liners.

acoustic↗