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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS2011

Laser-Induced Thermal Acoustics Theory and Expected Experimental Errors when Applied to a Scramjet Isolator Model

A scramjet isolator model test apparatus is being assembled in the Isolator Dynamics Research Lab (IDRL) at the NASA Langley Research Center in Hampton, Virginia. The test apparatus is designed to support multiple measurement techniques for investigating the flow field in a scramjet isolator model. The test section is 1-inch high by 2-inch wide by 24-inch long and simulates a scramjet isolator with an aspect ratio of two. Unheated, dry air at a constant stagnation pressure and temperature is delivered to the isolator test section through a Mach 2.5 planar nozzle. The isolator test section is mechanically back-pressured to contain the resulting shock train within the 24-inch isolator length and supports temperature, static pressure, and high frequency pressure measurements at the wall. Additionally, nonintrusive methods including laser-induced thermal acoustics (LITA), spontaneous Raman scattering, particle image velocimetry, and schlieren imaging are being incorporated to measure off-wall fluid dynamic, thermodynamic, and transport properties of the flow field. Interchangeable glass and metallic sidewalls and optical access appendages permit making multiple measurements simultaneously. The measurements will be used to calibrate computational fluid dynamics turbulence models and characterize the back-pressured flow of a scramjet isolator. This paper describes the test apparatus, including the optical access appendages; the physics of the LITA method; and estimates of LITA measurement uncertainty for measurements of the speed of sound and temperature.

Middleton, Troy F.↗
NASA NTRS2011

Autonomous Phase Retrieval Calibration

The Palomar Adaptive Optics System actively corrects for changing aberrations in light due to atmospheric turbulence. However, the underlying internal static error is unknown and uncorrected by this process. The dedicated wavefront sensor device necessarily lies along a different path than the science camera, and, therefore, doesn't measure the true errors along the path leading to the final detected imagery. This is a standard problem in adaptive optics (AO) called "non-common path error." The Autonomous Phase Retrieval Calibration (APRC) software suite performs automated sensing and correction iterations to calibrate the Palomar AO system to levels that were previously unreachable.

Estlin, Tara A.↗
NASA NTRS1989

Site selection criteria for the optical atmospheric visibility monitoring telescopes

A description of each of the criteria used to decide where to locate the Atmospheric Visibility Monitoring (AVM) telescope systems is given, along with a weighting factor for each of them. These criteria include low probability of clouds, fog, smog, haze, low scattering, low turbulence, availability of security and maintenance, and suitability of a site for a potential optical reception station. They will be used to determine which three of several sites under consideration will be used for monitoring visibility through the atmosphere as it applies to an optical ground-based receiving network as may be used in NASA space missions in decades to come.

Cowles, K.↗
DOE OSTI2023

Sequence2Self: Self-supervised image sequence denoising of pixel-level spray breakup morphology

Optical imaging of fast and transient phenomena such as the turbulent breakup of liquid sprays exhibit low signal-to-noise ratios due to the limited illumination intensity relative to the short exposure time. Image denoising is required to facilitate physical studies over these data but is challenging due to the absence of clean ground-truths and the stringency of the denoising task (e.g., strong and complex noise, limited resolution, preserving physical fidelity), preventing supervised and existing un-/self-supervised deep learning methods. To this end, Sequence2Self (Seq2S) is proposed, an extension of Self2Self (S2S) to image sequences that leverages both the signal’s spatial and temporal correlation. Seq2S is demonstrated on time-resolved x-ray phase contrast imaging of liquid jet fuel sprays in a gas turbine combustor, which possesses all of challenges detailed above. Experiments are conducted across four fuels with different breakup morphology using various state-of-the-art methods. Overall, many of the methods failed and Seq2S was most successful: (1) Accurate spray structures were reconstructed with consistent evolution across frames void of artifacts. (2) The performance was robust, invariant to the hyperparameter choice. (3) Computational time is short and can be made eligible for real-time denoising. In particular, the images denoised by Seq2S showed spray droplet diameter distributions with near-zero Kullback–Leibler divergence (0.01 ± 0.01) to a cleaner reference, whereas the second best method yielded 0.06 ± 0.03. In conclusion, this suggests that Seq2S can be reliably used prior to subsequent quantitative spray analyses as it retains (if not, improves) the statistical physical properties of the data.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS1991

Simultaneous measurements of temperature and density in air flows using UV laser spectroscopy

The simultaneous measurement of temperature and density using laser-induced fluorescence of oxygen in combination with Q-branch Raman scattering of nitrogen and oxygen is demonstrated in a low-speed air flow. The lowest density and temperature measured in the experiment correspond to the freestream values at Mach 5 in the Ames 3.5-Foot Hypersonic Wind Tunnel for stagnation conditions of 100 atm and 1000 K. The experimental results demonstrate the viability of the optical technique for measurements that support the study of compressible turbulence and the validation of numerical codes in supersonic and hypersonic wind tunnel flows.

Fletcher, D. G.↗
NASA NTRS2021

Characterization of Chevron Nozzle Performance

The flow fields from a set of 50.8 mm diameter circular nozzles were characterized using both streamwise and cross-stream 3-component Stereo Particle Image Velocimetry (SPIV). The test matrix of nozzles included 15 different chevron nozzle designs and one baseline, circularly symmetric nozzle. Nozzle jet operating conditions ranged from acoustic Mach numbers of 0.9 to 1.5, with static temperature ratios ranging between 0.84 and 2.7. Detailed surveys of the single jet flows were performed to capture three-dimensional features of the turbulent exhaust jet evolution. Cross-flow planar measurements were obtained at twelve axial locations, ranging from 0.1 to 20 nozzle diameters downstream of the nozzle exit planes. Streamwise measurements, along the jet centerlines, were obtained at ten partially overlapping downstream locations, providing complete axial surveys over a region extending beyond 20 nozzle diameters downstream of the nozzle exit planes. In both optical configurations, the measurement planes were sized to completely capture the fully turbulent jet shear layer growth. The measured three-dimensional mean and turbulent velocity fields, along with computed second order statistics including axial vorticity and turbulent kinetic energy, were evaluated for all test points. Well-defined streamwise vortex structures in the jet shear layers were measured and reported.

Jet Noise↗
DOE OSTI2024

Overview of recent turbulence studies across multiple confinement modes at the ASDEX Upgrade tokamak using the Correlation Electron Cyclotron Emission diagnostic

This work presents an overview of recent and ongoing experimental measurements of core and edge turbulence across multiple confinement regimes using the Correlation Electron Cyclotron Emission (CECE) diagnostic at the ASDEX Upgrade (AUG) tokamak. A common goal among these investigations is to identify how the properties of the turbulent electron temperature fluctuations measured by CECE influence and regulate the unique transport characteristics of each confinement regime, including L-mode, I-mode, ELMy H-mode, and ELM-free H-mode. Optics and signal processing methods to aid in the analysis and interpretation of experimental turbulence results are also presented. These methods, and particularly the down-sampling and ensemble averaging method, are relevant to a wide variety of fusion and non-fusion applications.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1990

Noncoherent Combination Of Optical-Heterodyne Outputs

In proposed scheme for reception of amplitude- or frequency-modulated signals transmitted optically through atmosphere, main receiver aperture divided into subapertures equipped with receivers, and outputs of receivers combined noncoherently. Multiple subaperture receivers used instead of attempting to focus all light from single large aperture onto one receiver. Outputs of receivers combined after demodulation. System will not perform as well as fully coherent system, but surpasses single-large-aperture system in presence of atmospheric turbulence. Offers superior performance in presence of distorted wavefront and/or imperfect receiver optics.

Chen, Chien-Chung↗
NASA NTRS2007

Coadding Techniques for Image-based Wavefront Sensing for Segmented-mirror Telescopes

Image-based wavefront sensing algorithms are being used to characterize optical performance for a variety of current and planned astronomical telescopes. Phase retrieval recovers the optical wavefront that correlates to a series of diversity-defocused point-spread functions (PSFs), where multiple frames can be acquired at each defocus setting. Multiple frames of data can be coadded in different ways; two extremes are in "image-plane space," to average the frames for each defocused PSF and use phase retrieval once on the averaged images, or in "pupil-plane space," to use phase retrieval on every set of PSFs individually and average the resulting wavefronts. The choice of coadd methodology is particularly noteworthy for segmented-mirror telescopes that are subject to noise that causes uncorrelated motions between groups of segments. Using data collected on and simulations of the James Webb Space Telescope Testbed Telescope (TBT) commissioned at Ball Aerospace, we show how different sources of noise (uncorrelated segment jitter, turbulence, and common-mode noise) and different parts of the optical wavefront, segment and global aberrations, contribute to choosing the coadd method. Of particular interest, segment piston is more accurately recovered in "image-plane space" coadding, while segment tip/tilt is recovered in "pupil-plane space" coadding.

Smith, Scott↗
NASA NTRSDate not supplied

NASA’s Laser Communications Relay Demonstration (LCRD) Experiment Program: Characterization And Initial Operations

The National Aeronautics and Space Administration’s (NASA) Laser Communications Relay Demonstration (LCRD) completed the first 18 months of its Experiment Program in December 2023. The LCRD geosynchronous payload includes two laser communications terminals interconnected via an onboard electronic switch. The payload can relay information between any two of a set of three ground stations. Two optical ground stations are located in California and Hawaii, and an RF ground station is located in New Mexico. Experiments to date have included demonstration of optimetrics, demonstrations of Delay/Disruption Tolerant Networking (DTN), and measurements of the effects of the atmosphere (turbulence, weather) on the performance and availability of lasercom (pointing, tracking, communications, and adaptive optics). Furthermore, future operational scenarios including robotic and exploration missions with various network service configurations have been emulated. This paper provides an overview and highlights of the first 18 months of LCRD experiments, and a preview of the upcoming experiments, including relaying data to and from the Integrated LCRD Low-Earth Orbit (LEO) User Modem and Amplifier Terminal (ILLUMA-T) on the International Space Station. LCRD is a joint project involving NASA Goddard Space Flight Center (GSFC), the California Institute of Technology Jet Propulsion Laboratory (JPL), and Massachusetts Institute of Technology Lincoln Laboratory (MIT LL).

David J. Israel↗
NASA NTRS1974

Investigation of acoustic radiation from supersonic turbulent jets by double-pulse holographic interferometry

A new experimental method was used to optically investigate the acoustic field radiated from supersonic jets. The method utilizes a pulse ruby laser to obtain double exposure holograms of the sound field of a supersonic jet. The jet remains on during both exposures thus eliminating the no-flow exposure. The time separation between the pulses can be varied depending on the spectral component of the radiation to be observed. Optical records were obtained for supersonic jets with exit Mach number 1.0, 1.5 and 2.0. It was found that high frequency acoustic radiation mainly originates from the regions near the nozzle exit, whereas the low frequency noise is generated from regions further downstream. These findings are consistent with the acoustic data obtained by other investigators.

Ozkul, A.↗
NASA NTRS1996

Atmospheric Turbulence Statistics from GOLD Experiments

Ground-Orbiter Lasercomm Demonstration (GOLD) includes the following: (1) Optical communication experiments between Table Mountain Observatory (TMF) and Japanese Engineering Test Satellite (ETS-VI); (2) International cooperative effort between NASA, NASDA, CRL and JPL; and (3) Phase 1 transmissions from October 1995 to January 1996 and Phase 2 transmissions from March 1996 to May 1996.

Jeganathan, Muthu↗
NASA NTRS1980

Unsteady density and velocity measurements in the 6 foot x 6 foot wind tunnel

The methods used and the results obtained in four aero-optic tests are summarized. It is concluded that the rather large values of density fluctuation appear to be the result of much higher Mach number than freestream and the violent turbulence in the flow as it separates from the turret. A representative comparison of fairing on-fairing off rms density fluctuation indicates essentially no effect at M = 0.62 and a small effect at M = 0.95. These data indicate that some slight improvement in optical quality can be expected with the addition of a fairing, although at M = 0.62 its effect would be nil. Fairings are very useful in controlling pressure loads on turrets, but will not have first order effects on optical quality. Scale sizes increase dramatically with increasing azimuth angle for a reprensentative condition. Since both scale sizes and fluctuation levels increase (total turbulence path length also increases) with azimuth angle, substantial optical degradation might be expected. For shorter wave lengths, large degradations occur.

Rose, W. C.↗
NASA NTRS1983

Dissipation of thick accretion disks

A thick accretion disk which is isentropic cannot have simple laminar flow because fluid elements follow orbits which intersect the orbits of other fluid elements, leading to turbulence in astrophysical disks which have very large Reynolds numbers. The turbulence in such disks is estimated using molecular analogies for the behavior of the fluid elements. The usual empirical dissipation parameter 'alpha' is found to be equal to 0.25 under normal circumstances. Characteristic local disk parameters are calculated for a variety of conditions at different distances from a central star of one solar mass. Circumstances involving low midplane optical depths or external heating which can lead to large reductions in the turbulence are discussed.

Cameron, A. G. W.↗
DOE OSTI2026

Neutrinos and Gamma Rays from Seyfert Galaxies Constrain the Properties of Coronal Turbulence

The TeV neutrino signal observed by IceCube from the active galactic nucleus NGC 1068 can probe its innermost coronal regions. If these neutrinos originate from hadrons accelerated within a magnetized turbulent corona, their intensity and spectrum depend on the turbulent magnetic field strength and turbulence coherence scale. The gamma rays accompanying neutrino production are absorbed in this optically thick environment, in a way that depends sensitively on the size of the corona. By a joint fit of the IceCube and Fermi-LAT observations, we translate the multimessenger signal from NGC 1068 and the tentative signal from NGC 7469 into quantitative constraints on coronal properties. NGC 1068, with a significant TeV neutrino excess, favors a compact, strongly magnetized corona with a large turbulence coherence length relative to the coronal size. NGC 7469, with two ∼100 TeV neutrino events, points instead to a somewhat larger corona with much smaller coherence length and high magnetization, but a very small fraction of energy in nonthermal protons. We obtain the diffuse flux from a population of Seyfert galaxies identical to either NGC 1068 or NGC 7469. Finally, we consider a third scenario, motivated by the spectral break observed in the diffuse neutrino flux at tens of TeV, with coronal properties intermediate between the two point-source-inspired models. To enable detailed comparisons with the IceCube and electromagnetic observations, we release our model predictions in a GitHub repository.

Testagrossa, Federico [Deutsches Elektronen-Synchr↗
NASA NTRS1990

Origin and dynamics of emission line clouds in cooling flow environments

The author suggests that since clouds are born co-moving in a turbulent intra-cluster medium (ICM), the allowed parameter space can now be opened up to a more acceptable range. Large-scale motions can be driven in the central parts of cooling flows by a number of mechanisms including the motion of the central and other galaxies, and the dissipation of advected, focussed rotational and magnetic energy. In addition to the velocity width paradox, two other paradoxes (Heckman et al. 1989) can be solved if the ICM is turbulent. Firstly, the heating source for the emission line regions has always been puzzling - line luminosities are extremely high for a given (optical or radio) galaxy luminosity compared to those in non-cooling flow galaxies, therefore a mechanism peculiar to cooling flows must be at work. However most, if not all, previously suggested heating mechanisms either fail to provide enough ionization or give the wrong line ratios, or both. The kinetic energy in the turbulence provides a natural energy source if it can be efficiently converted to cloud heat. Researchers suggest that this can be done via magneto-hydrodynamic waves through plasma slip. Secondly, while the x ray observations indicate extended mass deposition, the optical line emission is more centrally concentrated. Since many of the turbulence-inducing mechanisms are strongest in the central regions of the ICM, so is the method of heating. In other words material is dropping out everywhere but only being lit up in the center.

Loewenstein, Michael↗