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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Bearing defect signature analysis using advanced nonlinear signal analysis in a controlled environment

Utilizing high-frequency data from a highly instrumented rotor assembly, seeded bearing defect signatures are characterized using both conventional linear approaches, such as power spectral density analysis, and recently developed nonlinear techniques such as bicoherence analysis. Traditional low-frequency (less than 20 kHz) analysis and high-frequency envelope analysis of both accelerometer and acoustic emission data are used to recover characteristic bearing distress information buried deeply in acquired data. The successful coupling of newly developed nonlinear signal analysis with recovered wideband envelope data from accelerometers and acoustic emission sensors is the innovative focus of this research.

Zoladz, T.↗
NASA NTRS1995

Comparison of spatial numerical operators for duct-nozzle acoustics

A production Navier-Stokes/Euler CFD code, NASTD, developed for aircraft flowfield analysis has been modified to analyze acoustic fields associated with propulsion exhaust systems. The modified code has been applied to the Category 5 nozzle problem using six different spatial discretization schemes combined with a third-order, compact storage Runge-Kutta time integration. NASTD was found capable of tracking pressure disturbances normalized by the freestream value of order 10(exp -6), even with lower-order schemes, for the benchmark problem.

Cain, A. B.↗
NASA NTRS1976

Methods utilized in evaluating the profitability of commercial space processing

Profitability analysis is applied to commercial space processing on the basis of business concept definition and assessment and the relationship between ground and space functions. Throughput analysis is demonstrated by analysis of the space manufacturing of surface acoustic wave devices. The paper describes a financial analysis model for space processing and provides key profitability measures for space processed isoenzymes.

Bloom, H. L.↗
NASA NTRS1998

Fastrac Rocket Engine Combustion Chamber Acoustic Cavities

A three dimensional modal analysis was performed using finite fluid elements. The analysis shows four distinct modes of the Fastrac chamber plus cavities near the frequency of the chamber first tangential mode. The mode shapes illustrate the complexity of fluid oscillations in a three dimensional chamber and acoustic cavity. In addition, a first tangential forcing function was applied to the chamber with three different acoustic cavity fluid temperatures. It was observed that the acoustic cavity fluid temperature has a significant effect on the response of the chamber to first tangential mode oscillations.

Christensen, Eric↗
NASA NTRS1981

Acoustic and aerodynamic performance investigation of inverted velocity profile coannular plug nozzles

The results of model scale parametric static and wind tunnel aerodynamic performance tests on unsuppressed coannular plug nozzle configurations with inverted velocity profile are discussed. The nozzle configurations are high-radius-ratio coannular plug nozzles applicable to dual-stream exhaust systems typical of a variable cycle engine for Advanced Supersonic Transport application. In all, seven acoustic models and eight aerodynamic performance models were tested. The nozzle geometric variables included outer stream radius ratio, inner stream to outer stream ratio, and inner stream plug shape. When compared to a conical nozzle at the same specific thrust, the results of the static acoustic tests with the coannular nozzles showed noise reductions of up to 7 PNdB. Extensive data analysis showed that the overall acoustic results can be well correlated using the mixed stream velocity and the mixed stream density. Results also showed that suppression levels are geometry and flow regulation dependent with the outer stream radius ratio, inner stream-to-outer stream velocity ratio and inner stream velocity ratio and inner stream plug shape, as the primary suppression parameters. In addition, high-radius ratio coannular plug nozzles were found to yield shock associated noise level reductions relative to a conical nozzle. The wind tunnel aerodynamic tests showed that static and simulated flight thrust coefficient at typical takeoff conditions are quite good - up to 0.98 at static conditions and 0.974 at a takeoff Mach number of 0.36. At low inner stream flow conditions significant thrust loss was observed. Using an inner stream conical plug resulted in 1% to 2% higher performance levels than nozzle geometries using a bent inner plug.

Knott, P. R.↗
NASA NTRS2012

Numerical Study of Pressure Fluctuations due to High-Speed Turbulent Boundary Layers

Direct numerical simulations (DNS) are used to examine the pressure fluctuations generated by fully developed turbulence in supersonic turbulent boundary layers with an emphasis on both pressure fluctuations at the wall and the acoustic fluctuations radiated into the freestream. The wall and freestream pressure fields are first analyzed for a zero pressure gradient boundary layer with Mach 2.5 and Reynolds number based on momentum thickness of approximately 2835. The single and multi-point statistics reported include the wall pressure fluctuation intensities, frequency spectra, space-time correlations, and convection velocities. Single and multi-point statistics of surface pressure fluctuations show good agreement with measured data and previously published simulations of turbulent boundary layers under similar flow conditions. Spectral analysis shows that the acoustic fluctuations outside the boundary layer region have much lower energy content within the high-frequency region. The space-time correlations reflect the convective nature of the pressure field both at the wall and in the freestream, which is characterized by the downstream propagation of pressure-carrying eddies. Relative to those at the wall, the pressure-carrying eddies associated with the freestream signal are larger and convect at a significantly lower speed. The preliminary DNS results of a Mach 6 boundary layer show that the pressure rms in the freestream region is significantly higher than that of the lower Mach number case.

Duan, Lian↗
NASA NTRS2003

Vibroacoustic analysis and experimental validation of the structural responses of NASA Mars Exploration Rover spacecraft due to acoustic launch load

Structural responses of a spacecraft during liftoff are dominated by the intense acoustic pressure field imping on the exterior of the launch vehicle. Statistical Energy Analysis model of the NASA Mars Exploration Rover spacecraft has been developed and the SEA model was analyzed to predict vibroacoustic responses of the spacecraft under the diffuse acoustic loading condition.

vibroacoustic statistical energy analysis SEA↗
NASA NTRS2003

Vibroacoustic analysis and experimental validation of the structural responses of NASA Mars Exploration Rover spacecraft due to acoustic launch load

Structural responses of a spacecraft during liftoff are dominated by the intense acoustic pressure field imping on the exterior of the launch vehicle. Statistical Energy Analysis model of the NASA Mars Exploration Rover spacecraft has been developed and the SEA model was analyzed to predict vibroacoustic responses of the spacecraft under the diffuse acoustic loading condition.

vibroacoustic statistical energy analysis SEA↗
NASA NTRS2010

Use of Modal Acoustic Emission to Monitor Damage Progression in Carbon Fiber/Epoxy and Implications for Composite Structures

Broad-band modal acoustic emission (AE) data was used to characterize micromechanical damage progression in uniaxial IM7 and T1000 carbon fiber-epoxy tows and an IM7 composite overwrapped pressure vessel (COPV) subjected to an intermittent load hold tensile stress profile known to activate the Felicity ratio (FR). Damage progression was followed by inspecting the Fast Fourier Transforms (FFTs) associated with acoustic emission events. FFT analysis revealed the occurrence of cooperative micromechanical damage events in a frequency range between 100 kHz and 1 MHz. Evidence was found for the existence of a universal damage parameter, referred to here as the critical Felicity ratio, or Felicity ratio at rupture (FR*), which had a value close to 0.96 for the tows and the COPV tested. The implications of using FR* to predict failure in carbon/epoxy composite materials and related composite components such as COPVs are discussed. Trends in the FFT data are also discussed; namely, the difference between the low and high energy events, the difference between early and late-life events, comparison of IM7 and T1000 damage progression, and lastly, the similarity of events occurring at the onset of significant acoustic emission used to calculate the FR.

Waller, J. M.↗
NASA NTRS2000

Application of the Spectral Element Method to Acoustic Radiation

This report summarizes research to develop a capability for analysis of interior noise in enclosed structures when acoustically excited by an external random source. Of particular interest was the application to the study of noise and vibration transmission in thin-walled structures as typified by aircraft fuselages. Three related topics are focused upon. The first concerns the development of a curved frame spectral element, the second shows how the spectral element method for wave propagation in folded plate structures is extended to problems involving curved segmented plates. These are of significance because by combining these curved spectral elements with previously presented flat spectral elements, the dynamic response of geometrically complex structures can be determined. The third topic shows how spectral elements, which incorporate the effect of fluid loading on the structure, are developed for analyzing acoustic radiation from dynamically loaded extended plates.

Doyle, James F.↗
NASA NTRS1987

NORSTAR Project: Norfolk public schools student team for acoustical research

Development of the NORSTAR (Norfolk Public Student Team for Acoustical Research) Project includes the definition, design, fabrication, testing, analysis, and publishing the results of an acoustical experiment. The student-run program is based on a space flight organization similar to the Viking Project. The experiment will measure the scattering transfer of momentum from a sound field to spheres in a liquid medium. It is hoped that the experimental results will shed light on a difficult physics problem - the difference in scattering cross section (the overall effect of the sound wave scattering) for solid spheres and hollow spheres of differing wall thicknesses.

Fortunato, Ronald C.↗
NASA NTRS2014

Acoustics of Jet Surface Interaction-Scrubbing Noise

Concepts envisioned for the future of civil air transport consist of unconventional propulsion systems in the close proximity of the structure or embedded in the airframe. While such integrated systems are intended to shield noise from community, they also introduce new sources of sound. Sound generation due to interaction of a jet flow past a nearby solid surface is investigated here using the generalized acoustic analogy theory. The analysis applies to the boundary layer noise generated at and near a wall, and excludes the scattered noise component that is produced at the leading or the trailing edge. While compressibility effects are relatively unimportant at very low Mach numbers, frictional heat generation and thermal gradient normal to the surface could play important roles in generation and propagation of sound in high speed jets of practical interest. A general expression is given for the spectral density of the far field sound as governed by the variable density Pridmore-Brown equation. The propagation Greens function is solved numerically for a high aspect-ratio rectangular jet starting with the boundary conditions on the surface and subject to specified mean velocity and temperature profiles between the surface and the observer. It is shown the magnitude of the Greens function decreases with increasing source frequency andor jet temperature. The phase remains constant for a rigid surface, but varies with source location when subject to an impedance type boundary condition. The Greens function in the absence of the surface, and flight effect are also investigated.

Propulsion Noise↗
NASA NTRS2014

Acoustics of Jet Surface Interaction - Scrubbing Noise

Concepts envisioned for the future of civil air transport consist of unconventional propulsion systems in the close proximity to the structure or embedded in the airframe. While such integrated systems are intended to shield noise from the community, they also introduce new sources of sound. Sound generation due to interaction of a jet flow past a nearby solid surface is investigated here using the generalized acoustic analogy theory. The analysis applies to the boundary layer noise generated at and near a wall, and excludes the scattered noise component that is produced at the leading or the trailing edge. While compressibility effects are relatively unimportant at very low Mach numbers, frictional heat generation and thermal gradient normal to the surface could play important roles in generation and propagation of sound in high speed jets of practical interest. A general expression is given for the spectral density of the far field sound as governed by the variable density Pridmore-Brown equation. The propagation Green's function is solved numerically for a high aspect-ratio rectangular jet starting with the boundary conditions on the surface and subject to specified mean velocity and temperature profiles between the surface and the observer. It is shown the magnitude of the Green's function decreases with increasing source frequency and/or jet temperature. The phase remains constant for a rigid surface, but varies with source location when subject to an impedance type boundary condition. The Green's function in the absence of the surface, and flight effects are also investigated

Jet Noise↗
NASA NTRS1981

Inverse scattering for an exterior Dirichlet program

Scattering due to a metallic cylinder which is in the field of a wire carrying a periodic current is considered. The location and shape of the cylinder is obtained with a far field measurement in between the wire and the cylinder. The same analysis is applicable in acoustics in the situation that the cylinder is a soft wall body and the wire is a line source. The associated direct problem in this situation is an exterior Dirichlet problem for the Helmholtz equation in two dimensions. An improved low frequency estimate for the solution of this problem using integral equation methods is presented. The far field measurements are related to the solutions of boundary integral equations in the low frequency situation. These solutions are expressed in terms of mapping function which maps the exterior of the unknown curve onto the exterior of a unit disk. The coefficients of the Laurent expansion of the conformal transformations are related to the far field coefficients. The first far field coefficient leads to the calculation of the distance between the source and the cylinder.

Hariharan, S. I.↗
NASA NTRS1982

Acoustic waves in supernova remnants

When the Mach number of a supernova shock wave, propagating through the hot interstellar gas, is less than the critical value 2.76, the interaction of the shock with an interstellar cloud produces a reflected pressure pulse that propagates away from the cloud as an acoustic wave. A preliminary analysis indicates that about 4% of the energy of an exploding supernova shell is converted into such waves. When the postshock gas temperature exceeds 2 x 10 to the 6th K, waves as short as 6 pc are damped in less than a wavelength, returning the energy to the hot gas. Longer waves, especially at late stages, are less strongly damped, and are superposed in the hot gas to create a fluctuating magnetoacoustic field, with typical periods of about 100,000 years. In the warm neutral clouds at temperatures of about 8000 K these waves are rapidly damped by plasma slip (ambipolar diffusion), providing a heat source that may account for the temperatures of these clouds.

Spitzer, L., Jr.↗
NASA NTRS1986

Interaction of airborne and structureborne noise radiated by plates. Volume 1: Analytical study

The interaction of airborne and structureborne noise radiated by aircraft materials was examined. The theory and results of several computer simulations of the noise radiated by thin, isotropic, rectangular aluminum plates due to fully coherent combined acoustic and vibrational inputs is presented. The most significant finding was the extremely large influence that the relative phase between inputs has on the combined noise radiation of the plates. Phase dependent effects manifest themselves as cross terms in both the dynamic and acoustic portions of the analysis. Computer simulations show that these cross terms can radically alter the combined sound power radiated by plates constructed of aircraft-type materials. The results suggest that airborne-structureborne interactive effects could be responsible for a significant portion of the overall noise radiated by aircraft-type structures in the low frequency regime. This implies that previous analytical and experimental studies may have neglected an important physical phenomenon in the analayses of the interior noise of propeller dirven aircraft.

Mcgary, M. C.↗