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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 1,747 records · Page 97
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Effect of Flight on Turbulence Statistics and Noise Sources in a Round Turbulent Jet

Turbulence statistics relevant to noise modeling and prediction are computed in a series near-sonic, unheated round jets in the presence of a flight stream using Large Eddy Simulation. The Naval Research Laboratory’s Jet Engine Noise REduction (JENRE®) code is used to obtain unsteady flow solutions which are post-processed for single- and two-point, space-time statistical quantities, including the nominal noise sources from an acoustic analogy formulation. Jets subject to three different flight-stream speeds, along with a baseline static case, are considered. The impact of flight-stream speed on mean flow and turbulence profiles and the amplitudes, length and time scales of Reynolds-stress auto co-variances are determined and scalings for representing the flight-stream effect are explored. The implications for source modeling in jet mixing noise predictions within an acoustic analogy formulation are discussed.

Jet noise↗
NASA NTRSDate not supplied

Effect of Flight on Turbulence Statistics and Noise Sources in a Round Turbulent Jet

Turbulence statistics relevant to noise modeling and prediction are computed in a series near-sonic, unheated round jets in the presence of a flight stream using Large Eddy Simulation. The Naval Research Laboratory’s Jet Engine Noise REduction (JENRE) code is used to obtain unsteady flow solutions which are post-processed for single- and two-point, space-time statistical quantities, including the nominal noise sources from an acoustic analogy formulation. Jets subject to three different flight-stream speeds, along with a baseline static case, are considered. The impact of flight-stream speed on mean flow and turbulence profiles and the amplitudes, length and time scales of Reynolds-stress auto co-variances are determined and scalings for representing the flight-stream effect are explored. The implications for source modeling in jet mixing noise predictions within an acoustic analogy formulation are discussed.

Jet noise↗
DOE OSTI2011

SHORT-WAVELENGTH ELECTROSTATIC FLUCTUATIONS IN THE SOLAR WIND

Hybrid Vlasov-Maxwell simulations have been used recently to investigate the dynamics of the solar-wind plasma in the tail at short wavelengths of the energy cascade. These simulations have shown that a significant level of electrostatic activity is detected at wavelengths smaller than the proton inertial scale in the longitudinal direction with respect to the ambient magnetic field. In this paper, we describe the results of a new series of hybrid Vlasov-Maxwell simulations that allow us to investigate in more detail the generation process of these electrostatic fluctuations in terms of the electron-to-proton temperature ratio T{sub e} /T{sub p} . This analysis gives evidence for the first time that even in the case of cold electrons, T{sub e} {approx_equal} T{sub p} (the appropriate condition for solar-wind plasmas), the resonant interaction of protons with large-scale left-hand polarized ion-cyclotron waves is responsible for the excitation of short-scale electrostatic fluctuations with an acoustic dispersion relation. Moreover, through our numerical results we propose a physical mechanism to explain the generation of longitudinal proton-beam distributions in typical conditions of the solar-wind environment.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1995

Investigation of dispersion-relation-preserving scheme and spectral analysis methods for acoustic waves

Important characteristics of the aeroacoustic wave propagation are mostly encoded in their dispersion relations. Hence, a computational aeroacoustic (CAA) algorithm, which reasonably preserves these relations, was investigated. It was derived using an optimization procedure to ensure, that the numerical derivatives preserved the wave number and angular frequency of the differential terms in the linearized, 2-D Euler equations. Then, simulations were performed to validate the scheme and a compatible set of discretized boundary conditions. The computational results were found to agree favorably with the exact solutions. The boundary conditions were transparent to the outgoing waves, except when the disturbance source was close to a boundary. The time-domain data generated by such CAA solutions were often intractable until their spectra was analyzed. Therefore, the relative merits of three different methods were included in the study. For simple, periodic waves, the periodogram method produced better estimates of the steep-sloped spectra than the Blackman-Tukey method. Also, for this problem, the Hanning window was more effective when used with the weighted-overlapped-segment-averaging and Blackman-Tukey methods gave better results than the periodogram method. Finally, it was demonstrated that the representation of time domain-data was significantly dependent on the particular spectral analysis method employed.

Vanel, Florence O.↗
DOE OSTI2012

Determination of optical damage cross-sections and volumes surrounding ion bombardment tracks in GaAs using coherent acoustic phonon spectroscopy

We report the results of coherent acoustic phonon spectroscopy analysis of band-edge optical modification of GaAs irradiated with 400 keV Ne{sup ++} for doses between 10{sup 11}-10{sup 13} cm{sup -2}. We relate this optical modification to the structural damage density as predicted by simulation and verified by ion channeling analysis. Crystal damage is observed to cause optical modification that reduces the amplitude of the optoacoustic signal. The depth-dependent nature of the optoacoustic measurement allows us to determine optical damage cross-sections along the ion track, which are found to vary as a function of position along the track. Unexpectedly, we find that this optical modification is primarily dependent on the structural damage density and insensitive to the specific defect configuration along the ion track, suggesting that a simple model of defect density along the track is sufficient to characterize the observed optical changes. The extent of optical modification is strongly probe frequency-dependent as the frequency is detuned from the GaAs band edge. As determined from the experimental measurements, the spatial extent of optical modification exceeds the spatial extent of the structural disorder by an order of magnitude.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Decaying dark matter and the tension in σ{sub 8}

We consider decaying dark matter (DDM) as a resolution to the possible tension between cosmic microwave background (CMB) and weak lensing (WL) based determinations of the amplitude of matter fluctuations, σ{sub 8}. We perform N-body simulations in a model where dark matter decays into dark radiation and develop an accurate fitting formula for the non-linear matter power spectrum, which enables us to test the DDM model by the combined measurements of CMB, WL and the baryon acoustic oscillation (BAO). We employ a Markov chain Monte Carlo analysis to examine the overlap of posterior distributions of the cosmological parameters, comparing CMB alone with WL+BAO. We find an overlap that is significantly larger in the DDM model than in the standard CDM model. This may be hinting at DDM, although current data is not constraining enough to unambiguously favour a non-zero dark matter decay rate Γ. From the combined CMB+WL data, we obtain a lower bound Γ{sup −1}≥ 97 Gyr at 95 % C.L, which is less tight than the constraint from CMB alone.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1972

Preliminary noise tests of the engine-over-the-wing concept. i: 30 deg - 60 deg flap position

The results of preliminary acoustic tests of the engine over the wing concept are summarized. The tests were conducted with a small wing section model (32 cm chord) having two flaps set at the landing position, which is 30 and 60 deg respectively. The engine exhaust was simulated by an air jet from a convergent nozzle having a nominal diameter of 5.1 centimeters. Factors investigated for their effect on noise include nozzle location, wing shielding, flap leakage, nozzle shape, exhaust deflectors, and internally generated exhaust noise.

Reshotko, M.↗
NASA NTRS1985

A study of plasma expansion phenomena in laboratory generated plasma wakes - Preliminary results

The plasma expansion into the wake of a large rectangular plate immersed in a single-ion, collisionless, streaming plasma has been investigated in the laboratory. Several characteristics of the process involved in 'plasma expansion into vacuum' that have been predicted theoretically were observed, including the creation and motion of a rarefaction wave disturbance; the creation and motion of an expansion front; and the acceleration of ions into the wake at speeds above the ion-acoustic speed. The expansion was limited to early times; i.e., a few ion plasma periods, by the combination of plasma drift speed and vacuum chamber size. This prevented detailed comparison with self-similar theory, but results are in good agreement with numerical simulations and other laboratory experiments for the early time expansion. The conclusion is that the plasma expansion process is the dominant wake filling mechanism in the near wake of a body, whose potential is approximately the plasma space potential.

Wright, K. H., Jr.↗
NASA NTRS1990

High speed turboprop aeroacoustic study (counterrotation). Volume 1: Model development

The isolated counterrotating high speed turboprop noise prediction program was compared with model data taken in the GE Aircraft Engines Cell 41 anechoic facility, the Boeing Transonic Wind Tunnel, and in NASA-Lewis' 8x6 and 9x15 wind tunnels. The predictions show good agreement with measured data under both low and high speed simulated flight conditions. The installation effect model developed for single rotation, high speed turboprops was extended to include counterotation. The additional effect of mounting a pylon upstream of the forward rotor was included in the flow field modeling. A nontraditional mechanism concerning the acoustic radiation from a propeller at angle of attach was investigated. Predictions made using this approach show results that are in much closer agreement with measurement over a range of operating conditions than those obtained via traditional fluctuating force methods. The isolated rotors and installation effects models were combines into a single prediction program, results of which were compared with data taken during the flight test of the B727/UDF engine demonstrator aircraft. Satisfactory comparisons between prediction and measured data for the demonstrator airplane, together with the identification of a nontraditional radiation mechanism for propellers at angle of attack are achieved.

Whitfield, C. E.↗
NASA NTRS1994

A non-local computational boundary condition for duct acoustics

A non-local boundary condition is formulated for acoustic waves in ducts without flow. The ducts are two dimensional with constant area, but with variable impedance wall lining. Extension of the formulation to three dimensional and variable area ducts is straightforward in principle, but requires significantly more computation. The boundary condition simulates a nonreflecting wave field in an infinite duct. It is implemented by a constant matrix operator which is applied at the boundary of the computational domain. An efficient computational solution scheme is developed which allows calculations for high frequencies and long duct lengths. This computational solution utilizes the boundary condition to limit the computational space while preserving the radiation boundary condition. The boundary condition is tested for several sources. It is demonstrated that the boundary condition can be applied close to the sound sources, rendering the computational domain small. Computational solutions with the new non-local boundary condition are shown to be consistent with the known solutions for nonreflecting wavefields in an infinite uniform duct.

Zorumski, William E.↗
NASA NTRS2001

Simulation of Physical Experiments in Immersive Virtual Environments

An object-oriented event-driven immersive Virtual environment is described for the creation of virtual labs (VLs) for simulating physical experiments. Discussion focuses on a number of aspects of the VLs, including interface devices, software objects, and various applications. The VLs interface with output devices, including immersive stereoscopic screed(s) and stereo speakers; and a variety of input devices, including body tracking (head and hands), haptic gloves, wand, joystick, mouse, microphone, and keyboard. The VL incorporates the following types of primitive software objects: interface objects, support objects, geometric entities, and finite elements. Each object encapsulates a set of properties, methods, and events that define its behavior, appearance, and functions. A container object allows grouping of several objects. Applications of the VLs include viewing the results of the physical experiment, viewing a computer simulation of the physical experiment, simulation of the experiments procedure, computational steering, and remote control of the physical experiment. In addition, the VL can be used as a risk-free (safe) environment for training. The implementation of virtual structures testing machines, virtual wind tunnels, and a virtual acoustic testing facility is described.

Noor, Ahmed K.↗
NASA NTRS2017

Acoustic Detection of Faults and Degradation in a High-Bypass Turbofan Engine during VIPR Phase III Testing

The Vehicle Integrated Propulsion Research (VIPR) Phase III project was executed at Edwards Air Force Base, California, by the National Aeronautics and Space Administration and several industry, academic, and government partners in the summer of 2015. One of the research objectives was to use external radial acoustic microphone arrays to detect changes in the noise characteristics produced by the research engine during volcanic ash ingestion and seeded fault insertion scenarios involving bleed air valves. Preliminary results indicate the successful acoustic detection of suspected degradation as a result of cumulative exposure to volcanic ash. This detection is shown through progressive changes, particularly in the high-frequency content, as a function of exposure to greater cumulative quantities of ash. Additionally, detection of the simulated failure of the 14th stage stability bleed valve and, to a lesser extent, the station 2.5 stability bleed valve, to their fully-open fail-safe positions was achieved by means of spectral comparisons between nominal (normal valve operation) and seeded fault scenarios.

noise spectra↗
DOE OSTI2018

Air-Coupled Nondestructive Evaluation Dissected

This work develops a two-dimensional theoretical model to simulate the behavior of a fully non-contact air-coupled nondestructive evaluation system for a thin isotropic plate. The model is divided into transmission, guided wave propagation and reception phase. The validation of the complete model was carried out by modeling the same system by means of finite element method using a Multiphysics software. In addition, the dependency of the generated Lamb waves on different transmitter’s parameters and incidence angle is thoroughly investigated. The results of the acoustic pressure excited by the transducer, the out-of-plane velocity amplitudes for the generated first antisymmetric Lamb wave mode, and the radiated pressure from the plate caused by the leaky Lamb wavefield were all compared between the two models and a reasonable degree of similarity was found.

42 ENGINEERING↗
DOE OSTI2014

Phonon transport in single-layer transition metal dichalcogenides: A first-principles study

Two-dimensional transition metal dichalcogenides (TMDCs) are finding promising electronic and optical applications due to their unique properties. In this letter, we systematically study the phonon transport and thermal conductivity of eight semiconducting single-layer TMDCs, MX{sub 2} (M = Mo, W, Zr, and Hf, X = S and Se), by using the first-principles-driven phonon Boltzmann transport equation approach. The validity of the single-mode relaxation time approximation to predict the thermal conductivity of TMDCs is assessed by comparing the results with the iterative solution of the phonon Boltzmann transport equation. We find that the phononic thermal conductivities of 2H-type TMDCs are above 50 W/mK at room temperature while the thermal conductivity values of the 1T-type TMDCs are much lower, when the size of the sample is 1 μm. A very high thermal conductivity value of 142 W/mK was found in single-layer WS{sub 2}. The large atomic weight difference between W and S leads to a very large phonon bandgap which in turn forbids the scattering between acoustic and optical phonon modes and thus resulting in very long phonon relaxation time.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

N-point statistics of large-scale structure in the Zel'dovich approximation

Motivated by the results presented in a companion paper, here we give a simple analytical expression for the matter n-point functions in the Zel'dovich approximation (ZA) both in real and in redshift space (including the angular case). We present numerical results for the 2-dimensional redshift-space correlation function, as well as for the equilateral configuration for the real-space 3-point function. We compare those to the tree-level results. Our analysis is easily extendable to include Lagrangian bias, as well as higher-order perturbative corrections to the ZA. The results should be especially useful for modelling probes of large-scale structure in the linear regime, such as the Baryon Acoustic Oscillations. We make the numerical code used in this paper freely available.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Acousto-exciton interaction in a gas of 2D indirect dipolar excitons in the presence of disorder

A theory for the linear and quadratic responses of a 2D gas of indirect dipolar excitons to an external surface acoustic wave perturbation in the presence of a static random potential is considered. The theory is constructed both for high temperatures, definitely greater than the exciton gas condensation temperature, and at zero temperature by taking into account the Bose–Einstein condensation effects. The particle Green functions, the density–density correlation function, and the quadratic response function are calculated by the “cross” diagram technique. The results obtained are used to calculate the absorption of Rayleigh surface waves and the acoustic exciton gas drag by a Rayleigh wave. The damping of Bogoliubov excitations in an exciton condensate due to theirs scattering by a random potential has also been determined.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1990

High speed turboprop aeroacoustic study (counterrotation). Volume 2: Computer programs

The isolated counterrotating high speed turboprop noise prediction program developed and funded by GE Aircraft Engines was compared with model data taken in the GE Aircraft Engines Cell 41 anechoic facility, the Boeing Transonic Wind Tunnel, and in the NASA-Lewis 8 x 6 and 9 x 15 wind tunnels. The predictions show good agreement with measured data under both low and high speed simulated flight conditions. The installation effect model developed for single rotation, high speed turboprops was extended to include counter rotation. The additional effect of mounting a pylon upstream of the forward rotor was included in the flow field modeling. A nontraditional mechanism concerning the acoustic radiation from a propeller at angle of attack was investigated. Predictions made using this approach show results that are in much closer agreement with measurement over a range of operating conditions than those obtained via traditional fluctuating force methods. The isolated rotors and installation effects models were combined into a single prediction program. The results were compared with data taken during the flight test of the B727/UDF (trademark) engine demonstrator aircraft.

Whitfield, C. E.↗
NASA NTRS2001

Large Eddy Simulation of a Near Sonic Turbulent Jet and Its Radiated Noise

In this paper numerical simulations are used to calculate the turbulence dynamics simultaneously with the sound field for a high-speed near-sonic (Ma=0.9) compressible jet at two Reynolds numbers of 3,600 and 72,000. LES (Large Eddy Simulation) in conjunction with accurate numerical schemes is used to calculate the unsteady flow and sound in the near field of the jet. It is shown that the jet mean parameters, mean velocity fields and turbulence statistics are in good agreement with experimental data and results from other simulations. The sound in the near-field is calculated directly from the simulations. The calculations are shown to capture the peak in the dilatation and pressure spectra around a Strouhal number St=0.25-0.3, in agreement with typical jet-noise spectra measured in experiments. Dilatation contours in the near-field show the formation of acoustic waves with a dominant wavelength of 3.2-4 jet diameters, corresponding to the peak in the dilatation spectra. As expected, the non-compact noise sources are found to be most dominant in the region corresponding to the end of the potential core. The contribution of the LES model to the radiated noise appears to be weak and does not contaminate the sound field with spurious high-frequency noise. However, the frequency spectra of the sound show a rapid falloff away from the peak frequency. This is attributed to the quasi-laminar state of the shear-layers in the region prior to potential core closure, and a possible effect of insufficient azimuthal resolution at the observed location. Further analysis of the effect of the LES model, especially at high frequencies, is needed.

Constantinescu, G. S.↗