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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 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Priority for empirical methods development

Several noise sources combine to make up the total helicopter noise spectrum. The sources that are most important to community annoyance are the tail rotor (discrete), main rotor (unsteady), and engine (unsteady). The periodic and broadband noise components of the helicopter rotor were enumerated, and an approach to rotorcraft noise prediction was discussed. Helicopter noise sources were prioritized, and design improvements to reduce noise were reviewed. Main rotor noise is believed to be the key to quieter helicopters since there are proven and relatively inexpensive ways to handle the tail rotor. Blade Vortex Interaction (BVI) noise is a problem to some extent with all helicopters, particularly in the descent mode. Methodology must be developed to allow forecast and control of this type of noise. Additional means of controlling it, such as reduced rotor speeds for terminal operations should also be pursued because they may be the most effective means of control and they apply to all helicopter models. Main rotor broadband noise is the limiting factor in overall helicopter noise generation. Development of semi-empirical methods to predict its behavior is necessary if results are to be achieved in the short time period available.

King, R. J.↗
NASA NTRS1984

Noise and performance characteristics of a model scale X-wing rotor system in hover

Noise data for the hover condition were measured for a 8 m diameter X-wing model rotor mounted on an outdoor whirl tower. The noise was found to be a function of operating condition, in general increasing with performance. The X-wing spectra obtained from narrowband and 1/3-octave band analyses were dominated by the blade passage frequency harmonics. The circulation control slot blowing produced 1 to 10 kHz broadband noise which exhibited a jet velocity to the 5.4 dependency. Under the rotor plane loading noise was dominant, except at low values of blade pressure ratio where a sharp decrease in the blade passage frequency harmonic levels was observed. In the rotor plane, the contribution of the broadband noise sources was greater than under the rotor plane. The X-wing rotor system in hover exhibited flexibility in operating conditions to achieve a specific level of performance. The high collective, low blade passage ratio combinations which meet a given level of performance were associated with low overall sound pressure levels.

Willshire, W. L., Jr.↗
NASA NTRS1984

Nuclear Science Symposium, 30th, and Symposium on Nuclear Power Systems, 15th, San Francisco, CA, October 19-21, 1983, Proceedings

The range of disciplines covered includes physics instrumentation, data acquisition, FASTBUS, radiation detectors, scintillators, photomultipliers and optical detectors, subnanosecond 2-D imaging, medical and health instrumentation, reactor instrumentation, and space instrumentation. Cerenkov detectors, the prevention and rate capability of breakdown processes in wire chambers, and an interactive parallel processor for data analysis are studied. Attention is also given to bismuth germanate's role in gamma-ray spectroscopy, and the construction of a broadband universal sampling head is described. Gamma-ray imaging with a rotating hexagonal uniform redundant array, and broadband X-ray astronomical spectrometry are considered.

Nakamura, M.↗
NASA NTRS1985

Frequency-Discriminating Acoustic-Event Counter

Broadband events rejected. Acoustic-event counter discriminates against signals that simultaneously exceed preset amplitude thresholds in both low and high-frequency bands of its spectrum. Counter acts as spectral analyzer for mechanical vibrations. In combination with broadband acoustic transducer discriminates between signals and noise in acoustical destructive or nondestructive testing, vibration monitoring for machinery, burglar alarms, and other monitoring/warning systems.

Sugg, F. E.↗
NASA NTRS1985

Contribution of tonal components to the overall loudness, annoyance and noisiness of noise: Relation between single tones and noise spectral shape

A large scale laboratory investigation of loudness, annoyance, and noisiness produced by single-tone-noise complexes was undertaken to establish a broader data base for quanitification and prediction of perceived annoyance of sounds containing tonal components. Loudness, annoyance, and noisiness were distinguished as separate, distinct, attributes of sound. Three different spectral patterns of broadband noise with and without added tones were studied: broadband-flat, low-pass, and high-pass. Judgments were obtained by absolute magnitude estimation supplement by loudness matching. The data were examined and evaluated to determine the potential effects of (1) the overall sound pressure level (SPL) of the noise-tone complex, (2) tone SPL, (3) noise SPL, (4) tone-to-noise ratio, (5) the frequency of the added tone, (6) noise spectral shape, and (7) subjective attribute judged on absolute magnitude of annoyance. Results showed that, in contrast to noisiness, loudness and annoyance growth behavior depends on the relationship between the frequency of the added tone and the spectral shape of the noise. The close correspondence between the frequency of the added tone and the spectral shape of the noise. The close correspondence between loundness and annoyance suggests that, to better understand perceived annoyance of sound mixtures, it is necessary to relate the results to basic auditory mechanisms governing loudness and masking.

Hellman, R. P.↗
NASA NTRS1984

Quantification of advanced turboprop aircraft flyover noise annoyance

A laboratory experiment was conducted to quantify the annoyance to advanced turboprop (propfan) aircraft flyover noise. A computer synthesis system was used to generate 45 realistic, time varying simulations of propeller aircraft flyover noise in which the tonal content was systematically varied to represent the factorial combinations of five fundamental frequencies, three frequency envelope shapes, and three tone-to-broadband noise ratios. In the experiment, 64 subjects judged the annoyance of recordings of the 45 synthesized flyover noises presented at three sound levels in a test facility which simulates the outdoor acoustic environment. Analyses of the judgements showed that frequency envelope shape did not significantly affect annoyance. The interaction of fundamental frequency with tone-to-broadband noise ratio did have a large and complex effect on annoyance. Duration corrected A-weighted sound pressure level with a modified tone correction predicted annoyance better than any other measurement procedure.

Mccurdy, D. A.↗
NASA NTRS1984

Large-scale coherent structure and far-field jet noise

The phenomenon of broadband noise amplification/suppression under controlled excitation is investigated. The suppression is found to occur only at low jet speeds when the exit boundary layer is laminar; excitation at a Strouhal St(theta) number of about 0.017 results in optimum suppression of the far-field broadband noise as well as of the near-flow-field turbulence. The noise amplification is found to be a function of the Mach number, the amplification is higher at higher Mach number for a given excitation Strouhal number and level. The amplification also depends on the Strouhal number (St D), the maximum occurring in the range 0.65-0.85. Vortex pairing induced by the excitation appears to be at the heart of the noise amplification phenomenon under excitation.

Zaman, K. B. M. Q.↗
NASA NTRS1985

Analysis of turbulent underexpanded jets. II - Shock noise features using SCIPVIS

SCIPVIS, the computational model discussed by Dash et al. (1985), is assessed in predicting the complicated flow structure associated with shock-containing plumes. In addition, the analysis in this study examines this code's applicability as a basic part of a program for estimating broadband shock noise radiation. The results of this study show that excellent agreement exists between predicted and measured static pressure distributions for both underexpanded and overexpanded flow cases considered. Of the three turbulence closure models incorporated in the SCIPVIS code, the kW model of Spalding produces the most uniform agreement with measurement. The k-epsilon-2 model of Launder consistently overestimates plume spreading for supersonic jets with exit Mach numbers in the 1-2 range. Dash's (1983) k-epsilon-2-cc, compressibility-corrected version of Launder's model underestimates plume spreading. Good qualitative agreement was also obtained between the measured longitudinal turbulence intensity and that predicted by the code for the same trial case. Comparison of measured and predicted broadband shock noise spectrum peak values were found to be in excellent agreement. This utilized a variant of the Harper-Bourne and Fisher (1973) phase-array model: the effective shock spacing was reinterpreted as the value of the end of the plume potential core, determined herein by the SCIPVIS code.

Seiner, J. M.↗
NASA NTRS1985

Colour, albedo and nucleus size of Halley's comet

Photometry of Halley's comet in the B, J, V, and K broadband filters during a time when the coma was very weak and presumed to contribute negligibly to the broadband photometry is reported. The V-J and J-K colors suggest that the color of the nucleus of Halley's comet is similar to that of the D-type asteroids, which in turn suggests that the surface of the nucleus has an albedo less than 0.1.

Cruikshank, D. P.↗
NASA NTRS1985

Comparison of advanced turboprop and conventional jet and propeller aircraft flyover noise annoyance: Preliminary results

A laboratory experiment was conducted to compare the flyover noise annoyance of proposed advanced turboprop aircraft with that of conventional turboprop and jet aircraft. The effects of fundamental frequency and tone-to-broadband noise ratio on advanced turboprop annoyance were also examined. A computer synthesis system is used to generate 18 realistic, time varying simulations of propeller aircraft takeoff noise in which the harmonic content is systematically varied to represent the factorial combinations of six fundamental frequencies ranging from 67.5 Hz to 292.5 Hz and three tone-to-broadband noise ratios of 0, 15, and 30 dB. These advanced turboprop simulations along with recordings of five conventional turboprop takeoffs and five conventional jet takeoffs are presented at D-weighted sound pressure levels of 70, 80, and 90 dB to 32 subjects in an anechoic chamber. Analyses of the subjects' annoyance judgments compare the three categories of aircraft and examine the effects of the differences in harmonic content among the advanced turboprop noises. The annoyance prediction ability of various noise measurement procedures and corrections is also examined.

Mccurdy, D. A.↗
NASA NTRS1986

El Nino and outgoing longwave radiation: An atlas of Nimbus-7 Earth radiation budget observations

Five years of broadband Earth Radiation Budget (ERB) measurements taken by the Nimbus-7 ERB experiment have been archived. This five year period included the 1982 to 1983 El Nino/Southern Oscillation event, which reached its peak in January 1983 (near the beginning of the fifth data year). An outgoing longwave radiation subset of the data, for the period June 1980 to October 1983, was processed to enhance spatial resolution. This atlas contains the analyses of the resultant fields. In addition, a set of anomaly maps, based on a definition of pre-El Nino climatology, is included. Together, these two sets of maps provide the first broadband glimpse of the terrestrial outgoing longwave radiation response to the El Nino event.

Kyle, H. L.↗
NASA NTRS1985

Structure in the DC and AC electric fields associated with the dayside cusp region

The cusp region as seen in the AC and DC electric fields is one of intense variation. The intensity peaks within the soft particle precipitation. The only AC signal that appears to be unique to the cusp is broadband ULF-ELF magnetic noise. Other types of emissions are also found at other local times at high latitudes. The pattern of these signals, especially that of ULF-ELF broadband electrostatic noise (BEN), distinguishes the cusp region from other regions. BEN signatures are indicators of magnetosheath-like soft particle precipitation but not necessarily of open field lines. In addition, large spike-like features in the DC electric field are seen near local magnetic noon which appear to be related to the large convective electric fields that have been observed at the magnetopause. These features are not necessarily tied to convection reversals, but may appear within broader regions of zonal convective flow.

Maynard, N. C.↗
NASA NTRS1986

Plasma wave observations at comet Giacobini-Zinner

The plasma wave instrument on the International Cometary Explorer (ICE) detected strong ion acoustic waves together with electromagnetic whistlers and low-level electron plasma oscillations when the spacecraft was within two million km of the nucleus of comet Giacobini-Zinner. As ICE approached the anticipated bow-shock location, electromagnetic and electrostatic wave levels increased significantly, but even amidst this turbulence, the wave instrument detected structures with familiar bow shock characteristics that were correlated with observations of localized electron heating phenomena. Just beyond the visible coma, high-amplitude broadband waves were detected accounting for the significant electron heating observed in this region. Near closest approach, broadband electrostatic noise was detected together with a changing pattern of weak electron plasma oscillations that yielded a density profile for the outer layers of the cold plasma tail. Near the tail axis, the plasma wave instrument also detected a nonuniform flux of dust impacts, and a preliminary profile of the Giacobini-Zinner dust distribution for micrometer-sized particles is presented.

Scarf, F. L.↗
NASA NTRS1985

Comparison of advanced turboprop and conventional jet and propeller aircraft flyover noise annoyance - Preliminary results

A laboratory experiment was conducted to compare the flyover noise annoyance of proposed advanced turboprop aircraft with that of conventional turboprop and jet aircraft. The effects of fundamental frequency and tone-to-broadband noise ratio on advanced turboprop annoyance were also examined. A computer synthesis system was used to generate 18 realistic, time varyring simulations of propeller aircraft takeoff noise in which the harmonic content was systematically varied to represent the factorial combinations of six fundamental frequencies ranging from 67.5 Hz to 292.5 Hz and three tone-to-broadband noise ratios of 0, 15, and 30 dB. These advanced turboprop simulations along with recordings of five conventional turboprop takeoffs and five conventional jet takeoffs were presented at D-weighted sound pressure levels of 70, 80, and 90 dB to 32 subjects in an anechoic chamber. Analyses of the subjects' annoyance judgments compare the three categories of aircraft and examine the effects of the differences in harmonic content among the advanced turboprop noises. The annoyance prediction ability of various noise measurement procedures and corrections is also examined.

Mccurdy, D. A.↗
NASA NTRS1987

Aircraft noise synthesis system

A second-generation Aircraft Noise Synthesis System has been developed to provide test stimuli for studies of community annoyance to aircraft flyover noise. The computer-based system generates realistic, time-varying, audio simulations of aircraft flyover noise at a specified observer location on the ground. The synthesis takes into account the time-varying aircraft position relative to the observer; specified reference spectra consisting of broadband, narrowband, and pure-tone components; directivity patterns; Doppler shift; atmospheric effects; and ground effects. These parameters can be specified and controlled in such a way as to generate stimuli in which certain noise characteristics, such as duration or tonal content, are independently varied, while the remaining characteristics, such as broadband content, are held constant. The system can also generate simulations of the predicted noise characteristics of future aircraft. A description of the synthesis system and a discussion of the algorithms and methods used to generate the simulations are provided. An appendix describing the input data and providing user instructions is also included.

Mccurdy, David A.↗
NASA NTRS1987

Aircraft noise synthesis system: Version 4 user instructions

A modified version of the Aircraft Noise Synthesis System with improved directivity and tonal content modeling has been developed. The synthesis system is used to provide test stimuli for studies of community annoyance to aircraft flyover noise. The computer-based system generates realistic, time-varying audio simulations of aircraft flyover noise at a specified observer location on the ground. The synthesis takes into account the time-varying aircraft position relative to the observer; specified reference spectra consisting of broadband, narrowband, and pure tone components; directivity patterns; Doppler shift; atmospheric effects; and ground effects. These parameters can be specified and controlled in such a way as to generate stimuli in which certain noise characteristics such as duration or tonal content are independently varied while the remaining characteristics such as broadband content are held constant. The modified version of the system provides improved modeling of noise directivity patterns and an increased number of pure tone components. User instructions for the modified version of the synthesis system are provided.

Mccurdy, David A.↗
NASA NTRS1986

Recent advances in aeroacoustics

The state of the art in theoretical and numerical models and experimentation on broadband noise propagation from high speed aircraft components such as jets and helicopter blades is detailed. Attention is given to noise produced by jets, shear layers and turbulence and to the acoustic properties of rotors. The generation and propagation of acoustic noise are discussed in terms of the evolution of concepts for flow-tone generation to include hydrodynamic instabilities. Consideration is also given to techniques for experimental studies and theoretical models for nonlinear features of acoustic propagation of broadband noise and acoustic propagation in partially-choked or soft-walled ducts.

Krothapalli, A.↗
NASA NTRS1986

Turbulent magnetic reconnection

The results of two-dimensional spectral-method MHD simulations of the effect of turbulence on magnetic-reconnection processes are presented in extensive graphs and tables and characterized in detail. In a periodic sheet-pinch configuration, early-onset, persistent turbulence is found to occur when a low level of broadband fluctuations is introduced into the initial data. Features observed include small-scale unsteady coherent electric-current and vorticity structures, enhanced viscous and resistive dissipation, unsteady and spatially asymmetric fluid flow, large-scale and small-scale magnetic islands, multiple X points, large-amplitude electric-field fluctuations, and spectral characteristics indicating that the turbulence is broadband in both spatial directions and similar to homogeneous MHD turbulence. The importance of reconnection for studies of solar, magnetospheric, and laboratory plasmas in inhomogeneous magnetic fields is indicated.

Matthaeus, W. H.↗