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At least 1,261 records · Page 70
All sourcesNASA NTRSDOE OSTI
NASA NTRS2021

The Acoustic Air-Jet Generator

This paper describes the development history, operation, and working principle of an acoustic air-jet generator, which can be used to produce high intensity, high frequency acoustic waves. Flow imaging experiments of the system are shown, and applications of the system for various fluid flows are presented. While previous articles on this system have been written in English by the author, this article provides the only documented explanation and implementation of the focusing schlieren system used for flow imaging of the system. This paper has been cited in early works on focusing schlieren as one of the first implementations of such a system, but has not been widely cited in the bulk of the literature on the focusing schlieren method (aside from a more recent M.S. thesis), perhaps due to the difficulty of accessing the paper or that no translation was available. The purpose of this translation is to provide an English version of the article for researchers interested in this work of Dr. Hartmann, and in particular the description of his focusing schlieren system and its application.

Julius Hartmann↗
NASA NTRS2023

Multiple Scattering Theory for Modeling Sonic Booms in Atmospheric Turbulence

Sonic booms are often modeled using Burgers equations accounting for dominant propagation effects. Scattering effects of turbulence, however, have not been incorporated into such equations, although these effects are ubiquitous in measured sonic booms. This paper formulates the mean scattering effects, including backscattering, using multiple scattering theory and ensemble averaging. It obtains an acousto-turbulence interaction energy representing the interaction of an acoustic wave field with a turbulence field. The interaction energy gives rise to a scattering wavenumber, a complex-valued correction to the free-space wavenumber. The scattering wavenumber leads to a dispersion and attenuation of the mean waveform due to backscattering, and can be obtained from a derived exact solution. An existing Burgers equation is extended to include the scattering effects of turbulence as an additional linear term. Numerical simulations of an N-wave and a low boom show that the mean scattering effects lead to shock thickening in the mean waveforms as well as reduce the peak amplitudes and total energy contents. The energy reduction is less severe in the low boom than in the N-wave and is dependent on the variance, correlation length, and thickness of the turbulence field.

sonic booms↗
NASA NTRSDate not supplied

Dynamic Bellows for a Pulse Tube Cryocooler Application

Electrified aircraft propulsion systems will require powertrain components that are both lightweight and highly efficient. NASA’s 1.4 MW High Efficiency Megawatt Motor (HEMM) has been designed to run at 6800 RPM with >98% efficiency and 16 kW/kg, achieving low losses by incorporating a cryocooler within its rotor shaft to cool superconducting DC windings. A pulse-tube cryocooler typically contains an oscillating piston that drives acoustic waves; however, leakage around the piston reduces the efficiency of the cryocooler. A metal bellows was designed to replace the piston to allow for little to no leakage. The requirements for this bellows were extreme in terms of displacement amplitude, oscillating pressure amplitude, temperature, and frequency. It was determined that an off-the-shelf edge-welded bellows would not work for this application, so a custom bellows was designed to include full convolutions welded only on their outer diameters where the stress is lower. Several high-fatigue-strength materials were considered, including 17-4PH H900 and Aermet 100. The final bellows design includes 74 convolutions with a variable inner diameter that helps distribute and reduce the dynamic stress throughout the length rather than concentrating the high stress in one location. To test the concept, a short 10-convolution bellows with constant inner diameter was designed for testing. One short bellows test article was fabricated with the outer diameter weld, and one by 3D printing. Both will be fatigue-tested with the goal of achieving 10^7 cycles.

Bellows↗
NASA NTRSDate not supplied

Accounting for the Influence of Decorrelation in Microphone Phased Array Deconvolution Methods

Microphone phased arrays are a common tool for use in aeroacoustic wind tunnel testing. The analysis of acquired array data is known to suffer from decorrelation effects, where the coherence of an acoustic wave measured by a pair of microphones is degraded as the wave passes through a turbulent free shear layer or boundary layer. This paper describes, in detail, how to mitigate the influence of decorrelation effects when processing array data with deconvolution methods. This is done using the DAMAS algorithm as an example, applied to recent airframe noise test data acquired in the NASA Langley 14- by 22-Foot Subsonic Tunnel. Two ways of handling the turbulent propagation modeling, both assuming plane wave propagation, are described. Results show that while turbulence model fit parameters may differ, both methods output extremely similar deconvolution results. Further improvements likely require more accurate mean shear layer data prior to developing more involved turbulence models.

microphone array↗
NASA NTRSDate not supplied

Phased Array Characterization of Slat Noise Radiation from a High-Lift Common Research Model

A test campaign was conducted in the open-jet test section of the NASA Langley 14- by 22-Foot Subsonic Tunnel on a 10%-scale, semispan version of a High-Lift Common Research Model (CRM-HL) incorporating a leading-edge slat, trailing-edge flap and removable high-fidelity main landing gear. Far field acoustic measurements were obtained on baseline and acoustically treated model configurations using a traversing 97-microphone phased array that viewed the pressure side of the airframe. A modified version of the DAMAS deconvolution method incorporating corrections for shear layer acoustic wave decorrelation was employed to determine the locations and strengths of relevant noise sources along the span of the slat and in the vicinity of the flap edges and landing gear. The main goal of the test campaign was to use the array data to evaluate the effectiveness of various slat noise reduction concepts. It was found that slat-gap fillers produced significant broadband noise reduction for all Mach numbers and airfoil angles of attack that were investigated. Mach number scaling revealed an approximate velocity to the sixth power relationship for the slat noise at higher frequencies. Directivity measurements obtained from integration of DAMAS pressure-squared values over defined geometric zones around the model showed that baseline slat noise radiation approximated a dipole as a function of polar emission angle, becoming approximately omnidirectional with the introduction of the slat-gap filler. The test campaign clearly demonstrated the noise reduction benefits that can be obtained by applying appropriate treatments to leading edge slats on commercial transport-class aircraft.

William M Humphreys, Jr.↗
NASA NTRS2022

Spectroscopic Study of Solar Transition Region Oscillations in the Quiet-Sun Observed By IRIS Using the Si IV Spectral Line

In this paper, we use the Si IV 1393.755 Å spectral line observed by the Interface Region Imaging Spectrograph (IRIS) in the quiet-Sun (QS) to determine the physical nature of the solar transition region (TR) oscillations. We analyse the properties of these oscillations using wavelet tools (e.g. power, cross-power, coherence, and phase difference) along with the stringent noise model (i.e. power law + constant). We estimate the period of the intensity and Doppler velocity oscillations at each chosen location in the QS and quantify the distribution of the statistically significant power and associated periods in one bright region and two dark regions. In the bright TR region, the mean periods in intensity and velocity are 7 min and 8 min, respectively. In the dark regions, the mean periods in intensity and velocity are 7 min and 5.4 min, respectively. We also estimate the phase difference between the intensity and Doppler velocity oscillations at each location. The statistical distribution of the phase difference is estimated, which peaks at −119° ± 13°, 33° ± 10°, 102° ± 10° in the bright region and at −153° ± 13°, 6° ± 20°, 151° ± 10° in the dark regions. The statistical distribution reveals that the oscillations are caused by propagating slow magneto-acoustic waves encountered with the TR. Some of these locations may also be associated with standing slow waves. Moreover, in the given time domain, several locations exhibit the presence of both propagating and standing oscillations at different frequencies.

MHD – Sun: oscillations↗
NASA NTRS2021

On the Presence and Thermalization of Cold Ions in the Exhaust of Antiparallel Symmetric Reconnection

Using fully kinetic 2.5 dimensional particle-in-cell simulations of anti-parallel symmetric magnetic reconnection, we investigate how initially cold ions are captured by the reconnection process, and how they evolve and behave in the exhaust. We find that initially cold ions can remain cold deep inside the exhaust. Cold ions that enter the exhaust downstream of active separatrices, closer to the dipolarization front, appear as cold counter-streaming beams behind the front. In the off-equatorial region, these cold ions generate ion-acoustic waves that aid in the thermalization both of the incoming and outgoing populations. Closest to the front, due to the stronger magnetization, the ions can remain relatively cold during the neutral plane crossing. In the intermediate exhaust, the weaker magnetization leads to enhanced pitch angle scattering and reflection. Cold ions that enter the exhaust closer to the X line, at active separatrices, evolve into a thermalized exhaust. Here, the cold populations are heated through a combination of thermalization at the separatrices and pitch angle scattering in the curved magnetic field around the neutral plane. Depending on where the ions enter the exhaust, and how long time they have spent there, they are accelerated to different energies. The superposition of separately thermalized ion populations that have been accelerated to different energies form the hot exhaust population.

Cecilia Norgren↗
NASA NTRSDate not supplied

Assessing Potential Geophysical and Environmental Impacts from Frequent Rocket Launch Missions at Kennedy Space Center

Kennedy Space Center (KSC) in Florida has been utilized for space missions over many years with a gradually increasing number of rocket launches. There have been multiple studies where air-coupled acoustic waves and infrasound originating from launched rockets were used for operational purposes, such as locating booster trajectories as a function of changing atmospheric conditions. However, no study has utilized the acoustoelastic waves as a signal source for subsurface seismic investigations. We conducted a dispersion analysis using the seismic energy recorded from the Artemis I rocket launch at KSC in November 2022, and from these results we generated depth-sensitivity kernels at different wave frequencies. The kernels were compared with sedimentary core data to verify boundaries of carbonate layers above the Floridan Aquifer System. Accumulative information of bedrock-sediment boundary across the sedimentary platform could especially provide geo-structural evidence that manifests the configuration of coastal features. Continuous dispersion analysis of seismic recordings from consecutive rocket launches also has potential to identify non-stationary environmental effects, such as reorientation of sedimentary structures and fluctuation of the saltwater/groundwater lens from gravitational tides, which may affect erosional susceptibility of coastal features.

Han Byul Woo↗
NASA NTRSDate not supplied

Assessing Potential Geophysical and Environmental Impacts from Frequent Rocket Launch Missions at Kennedy Space Center

Kennedy Space Center (KSC) in Florida has been utilized for space missions over many years with a gradually increasing number of rocket launches. There have been multiple studies where air-coupled acoustic waves and infrasound originating from launched rockets were used for operational purposes, such as locating booster trajectories as a function of changing atmospheric conditions. However, no study has utilized the acoustoelastic waves as a signal source for subsurface seismic investigations. We conducted a dispersion analysis using the seismic energy recorded from the Artemis I rocket launch at KSC in November 2022, and from these results we generated depth-sensitivity kernels at different wave frequencies. The kernels were compared with sedimentary core data to verify boundaries of carbonate layers above the Floridan Aquifer System. Accumulative information of bedrock-sediment boundary across the sedimentary platform could especially provide geo-structural evidence that manifests the configuration of coastal features. Continuous dispersion analysis of seismic recordings from consecutive rocket launches also has potential to identify non-stationary environmental effects, such as reorientation of sedimentary structures and fluctuation of the saltwater/groundwater lens from gravitational tides, which may affect erosional susceptibility of coastal features.

Rocket Launch Seismicity↗
NASA NTRSDate not supplied

Modification of Mach 6 Freestream Flow by Pitot Probe Bow Shock as Measured by Line FLDI and SAFS

Measurements of the flow in front of flat-face Pitot probes in NASA Langley ResearchCenter’s 20-Inch Mach 6 Air Tunnel were made using a 35-point line focused laser differentialinterferometer (FLDI), a two-point FLDI, and a self-aligned focusing schlieren system. Thesesystems were used to make measurements of flow unsteadiness between the bow shock andPitot probe face, while also probing the freestream region just upstream of the bow shock.Shock standoff distances from the non-intrusive measurements match closely with analyticalsolutions using the probe face diameter. Acoustic wave angles and velocities in the freestreamcompare favorably with DNS simulations of a Mach 6 freestream flow, and wave velocities in thepost-shock region slow as they approach the probe face. Peak frequencies in the post-shockregion as measured by FLDI compare favorably to the estimates computed from the shockstandoff distance for most probe diameters. With increasing unit Reynolds number, fluctuationintensities in the post-shock region were attenuated below the intensities of the freestream, witha spectral, spatial, and probe size dependence. Pitot probe power spectral density estimatesare presented from the test campaign, which can be compared with FLDI and SAFS data toevaluate the applicability of the transfer functions derived from computational simulations.

Joshua M Weisberger↗
DOE OSTI2021

Acoustic gas volume fraction measurement in a multiphase flowing liquid

Apparatus and methods for the measurement of gas volume fraction of produced oil are described. A first method measures the response of a pipe containing the produced oil excited by a source of vibration in the form of an acoustic frequency chirp containing a linearly varying range of frequencies in the tens of kilohertz range encompassing at least one resonant mode of the pipe. As the gas volume fraction increases, the location of the peak maximum of the measured frequency spectrum responsive to the excitation increases in frequency, and the height of the peak maximum increases, thereby permitting a linear calibration curve to be obtained. A second method measures the response of a pipe containing the produced oil to excitation by a continuous source of vibration having a chosen frequency above those which excite flexural vibrations in the pipe and simultaneously excite acoustic waves in the fluid contained in the pipe, known as the coincidence frequency. Gas present in the fluid will interrupt sound propagation or reverberation, thereby generating fluctuations in the amplitude of the measured vibrations of the pipe. The amplitude fluctuation level provides a measure of the gas volume present inside the pipe. A third method measures the response of a pipe containing the produced oil to excitation by a high-bandwidth, short pulse having a chosen center frequency above the coincidence frequency. Gas present in the fluid will interrupt pulse propagation, thereby generating fluctuations in the amplitude of the measured vibrations of the pipe.

Sinha, Dipen N.↗
DOE OSTI2021

Microwave diagnostics and passive sensors for pipeline, well-bore, and boiler-tube monitoring

Materials, methods of making, and methods of using an integrated wireless detector for real time interrogating metallic tubular structures comprising: an RF patch antenna; a passive surface acoustic wave (SAW) sensor; and data analytic methodologies. An embodiment relates to interrogating a metallic structure having a uniform cross section using an antenna which launches electromagnetic radiation. A sensor may be located within the structure is configured to re-emit electromagnetic radiation modified depending on parameters for which the sensor has been functionalized. An antenna may receive radiation as modified by the sensor, or may receive the transmitted or backscattered radiation directly, without use of a sensor. The antenna then communicates wirelessly with an interrogator providing data which may be used to understand the operational status of the structure in real-time.

Ohodnicki, Paul R.↗
DOE OSTI2022

Gas sensor and method of optimizing an array of gas sensors

A gas sensor (100,200) includes at least one sensor device including a surface acoustic wave (SAW) device (110) or a quartz crystal microbalance (QCM) device (210), and a layer of metal organic framework (MOF) material (120,220) disposed on each of the at least one sensor device. The at least one sensor device is structured to sense a change in mass of the MOF material.

Wilmer, Christopher E.↗
DOE OSTI2024

Effects of irradiation damage on the elastic properties and hardness of complex transition metal diborides

Multi-principal component transition metal (TM) diborides represent a class of high-entropy ceramics (HECs) that have received considerable interest in recent years owing to their promising properties for extreme environment applications that include thermal/ environmental barriers, hypersonic vehicles, turbine engines, and next-generation nuclear reactors. While the addition of chemical disorder through the random distribution of TM elements on the cation sublattice has offered opportunities to tailor elastic stiffness and hardness, the effects of irradiationinduced structural damage on the physical properties of these complex materials have remained largely unexplored. To this end, changes in the hardness and elastic moduli of a high-entropy TM diboride (Hf0.2Nb0.2Ta0.2Ti0.2Zr0.2)B2 and three of its quaternary subsets following irradiation with 10 MeV gold (Au) ions to fluences of up to 6 × 10^15 Au cm-2 are investigated at the micrometer and sub-micrometer length-scales via the dispersion of laser-generated surface acoustic waves (SAW) and nanoindentation, respectively. The nanoindentation measurements show that the TM diborides exhibit an initial increase in hardness following irradiation with energetic Au ions, with a subsequent decrease in hardness following further irradiation. One quaternary composition, (Hf1/3Ta1/3Ti1/3)B2, exhibits a notable exception to the trend and continues to exhibit an increase in hardness with ion irradiation fluence. Although differences in the absolute values of the effective elastic moduli obtained from the measured SAW dispersion and nanoindentation are observed (and attributed to microstructural variations at the measurement length-scale), both techniques yield similar trends in the form of an initial reduction and subsequent saturation in the elastic modulus with increasing ion irradiation fluence. The quaternary TM diboride (Hf1/3Ta1/3Ti1/3)B2 again exhibits a departure from this trend. The high-entropy TM diboride (Hf0.2Nb0.2Ta0.2Ti0.2Zr0.2)B2 exhibits the greatest recovery in hardness and modulus when irradiated to high ion fluences following initial changes at low fluence, indicating superior resistance to radiation-induced damage over its quaternary counterparts. Opportunities for designing HECs with superior hardness and modulus for enhanced radiation resistance (compared to their single constituent counterparts) by tailoring chemical disorder and bond character in the lattice are discussed.

36 - MATERIALS SCIENCE↗
NASA NTRS1990

Acoustic positioning and orientation prediction

A method is described for use with an acoustic positioner, which enables a determination of the equilibrium position and orientation which an object assumes in a zero gravity environment, as well as restoring forces and torques of an object in an acoustic standing wave field. An acoustic standing wave field is established in the chamber, and the object is held at several different positions near the expected equilibrium position. While the object is held at each position, the center resonant frequency of the chamber is determined, by noting which frequency results in the greatest pressure of the acoustic field. The object position which results in the lowest center resonant frequency is the equilibrium position. The orientation of a nonspherical object is similarly determined, by holding the object in a plurality of different orientations at its equilibrium position, and noting the center resonant frequency for each orientation. The orientation which results in the lowest center resonant frequency is the equilibrium orientation. Where the acoustic frequency is constant, but the chamber length is variable, the equilibrium position or orientation is that which results in the greatest chamber length at the center resonant frequency.

Barmatz, Martin B.↗
NASA NTRS2004

FUSE Cycle 3 Program CO22: Chromospheric Activity in Population II Giants

One of the mysteries of Population II giants is that they still show chromospheric emission despite their great age. The global dynamo which was active during their main-sequence lifetimes is expected to become extremely weak through magnetic rotational braking. The nature of the observed emission is not understood; although acoustic shock waves might provide the heating, acoustic waves are not predicted to drive the observed mass loss - which in turn requires the dissipation of magneto-hydrodynamic waves. This program was designed to search for the faint stellar H Ly(beta) emission wings and the fluorescent Fe II and H2 emission from one of the brightest, metal poor, Population II stars. These FUSE diagnostics, when combined with existing UV and optical spectra, help determine the major radiative cooling channels for the chromosphere. This observation was to complement that previously planned for the mildly metal deficient giant alpha Boo (K2 III). However, a Boo has yet to be observed with FUSE.

Harper, Graham M.↗
NASA NTRS2004

Chromospheric Activity in Population II Giants

One of the mysteries of Population II giants is that they still show chromospheric emission despite their great age. The global dynamo which was active during their main-sequence lifetimes is expected to become extremely weak through magnetic rotational braking. The nature of the observed emission is not understood; although acoustic shock waves might provide the heating, acoustic waves are not predicted to drive the observed mass loss - which in turn requires the dissipation of magneto-hydrodynamic waves. This program was designed to search for the faint stellar H Ly beta emission wings and the fluorescent Fe II and H2 emission from one of the brightest, metal poor, Population II stars. These FUSE diagnostics, when combined with existing UV and optical spectra, help determine the major radiative cooling channels for the chromosphere. This observation was to complement that previously planned for the mildly metal deficient giant alpha Boo (K2 III). However, alpha Boo has yet to be observed with FUSE.

Harper, Graham M.↗
DOE OSTI2022

Harvesting Wave Energy to Power Acoustic Transmitters Using Triboelectric Nanogenerator

Wave energy has the largest reserves and widest distribution among blue energy sources. However, the conversion and utilization of ocean wave energy are challenging. In this work, we developed a contact-separation mode triboelectric nanogenerator (TENG) with a simple structure for harvesting wave energy and powering marine sensors and transmitters and performed detailed electrical characterization under controlled laboratory conditions. A prototype power management circuit (PMC) was implemented to improve the output performance of the TENG. The output from the PMC could charge up a storage capacitor for powering sensors and electronics. Eventually, the TENG was integrated within a water-proof enclosure and tested using a custom-built wave simulator to evaluate the device performance in a more representative scenario. The device sustainably powered up an array of 27 LEDs and was able to charge up a capacitor up to 1.8 V for driving an acoustic transmitter. The results demonstrate that TENG technology shows great promise in harvesting low-frequency ocean wave energy.

Yang, Yang↗