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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 451 records · Page 25

Effect of Reynolds Number and Periodic Unsteady Wake Flow Condition on Boundary Layer Development, Separation, and Intermittency Behavior Along the Suction Surface of a Low Pressure Turbine Blade

The paper experimentally studies the effects of periodic unsteady wake flow and different Reynolds numbers on boundary layer development, separation and re-attachment along the suction surface of a low pressure turbine blade. The experimental investigations were performed on a large scale, subsonic unsteady turbine cascade research facility at Turbomachinery Performance and Flow Research Laboratory (TPFL) of Texas A&M University. The experiments were carried out at Reynolds numbers of 110,000 and 150,000 (based on suction surface length and exit velocity). One steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, wake velocities, and turbulence intensities were investigated. The reduced frequencies chosen cover the operating range of LP turbines. In addition to the unsteady boundary layer measurements, surface pressure measurements were performed. The inception, onset, and the extent of the separation bubble information collected from the pressure measurements were compared with the hot wire measurements. The results presented in ensemble-averaged, and the contour plot forms help to understand the physics of the separation phenomenon under periodic unsteady wake flow and different Reynolds number. It was found that the suction surface displayed a strong separation bubble for these three different reduced frequencies. For each condition, the locations defining the separation bubble were determined carefully analyzing and examining the pressure and mean velocity profile data. The location of the boundary layer separation was dependent of the Reynolds number. It is observed that starting point of the separation bubble and the re-attachment point move further downstream by increasing Reynolds number from 110,000 to 150,000. Also, the size of the separation bubble is smaller when compared to that for Re=110,000.

Schobeiri, M. T.↗

Discovery Of A Rossby Wave In Jupiter's South Equatorial Region

A detailed study of the chevron-shaped dark spots on the strong southern equatorial wind jet near 7.5 deg S planetographic latitude shows variations in velocity with longitude and time. The chevrons move with velocities near the maximum wind jet velocity of approx.140 m/s, as deduced by the history of velocities at this latitude and the magnitude of the symmetric wind jet near 7 deg N latitude. Their repetitive nature is consistent with an inertia-gravity wave (n = 75-100) with phase speed up to 25 m/s, relative to the local flow, but the identity of this wave mode is not well constrained. However, high spatial resolution movies from Cassini images show that the chevrons oscillate in latitude with a approx.7-day period. This oscillating motion has a wavelength of approx.20 deg and a speed of approx.100 m/s, following a pattern similar to that seen in the Rossby wave plumes of the North Equatorial Zone, and possibly reinforced by it, though they are not perfectly in phase. The transient anticyclonic South Equatorial Disturbance (SED) may be a similar wave feature, but moves at slower velocity. All data show chevron latitude variability, but it is unclear if this Rossby wave is present during other epochs, without time series movies that fully delineate it. In the presence of multiple wave modes, the difference in dominant cloud appearance between 7 deg N and 7.5 deg S may be due to the presence of the Great Red Spot, either through changes in stratification and stability or by acting as a wave boundary.

Simon-Miller, Amy A.↗

Characterization and Analysis of Phoca Vitulina, Zalophus Californianus and Mirounga Angustirostris Vibrissae

Vibrissae of Phoca Vitulina (harbor seal) and Mirounga Angustirostris (elephant seal) possess undulations along their length. Harbor seal vibrissae have shown potential to reduce vortex induced vibrations and reduce drag compared to cylinders and ellipses. The exact geometry of the whiskers has not been well documented and the parameters that are responsible for the reduction in drag and vortex induced vibrations have not been characterized. Samples of six harbor seal vibrissae, six elephant seal vibrissae and six California sea lion (Zalophus californianus) vibrissae were collected from the Marine Mammal Center in California. The objectives of this study were to (1) Compare measurement techniques for digitizing and extracting parameters of the seal whiskers for the PeTaL (Periodic Table of Life) database. CT scanning, microscopy and 3D scanning techniques were compared. (2) Compare aerodynamic characteristics of a representative harbor seal whisker, elephant seal whisker, California sea lion whisker and ellipse at Re = 12000 and Re = 23000 based on major axis and free stream velocity. The data (in appendices) is available to compare CFD models or for further experimental validation, (3) Show close up images of whiskers and look for surface roughness effects. Variations in the seven parameters of the seal whisker were observed that may either be a feature of the vibration reduction mechanism or a result of natural variation. It is hypothesized that six parameters are sufficient to characterize seal whiskers based on analytic fitting. The drag coefficient of harbor seal whiskers examined in this study were found to be 25 percent lower than that of an ellipse with comparable major and minor axis lengths at Reynolds number of 12000. The dissipation length scale was found to be larger for seal whiskers. Potential applications of seal whisker morphology for aerospace are discussed. Roughness is not thought to play a factor in seal hydrodynamics.

Shyam, Vikram↗

Introduction to Big Earth Data Applications

Climate and weather modeling generate enormous volumes that make iterative analysis challenging, spurring the development of new ways to work with the data. At the same time in the Earth Observation area, technology advances are enabling new sensors and satellites that will increase data volume, velocity and application variety. Scaling up can also be seen when operational applications expand from small, local studies to larger spatial scales with more analysis targets.

Christopher Lynnes↗

Progressive Damage and Failure Analysis of Thermoplastic Composites in Low Velocity Impact Using MAT299

As part of the NASA Hi-Rate Composite Aircraft Manufacturing (HiCAM) Project, state-of-the-art progressive damage and failure analysis (PDFA) tools developed for use with thermosets are being evaluated for use in modeling alternative material systems, like thermoplastics. Experimental low-velocity impact data of a thermoplastic material system, AS4D/PEKK-FC, is presented and includes characterization of the impact damage mechanisms as well as associated load and displacement data. Following the presentation of experimental results, two simulation approaches using the PDFA tool MAT299 in the commercial off-the-shelf finite element software LS-DYNA are employed to predict damage area and force-displacement responses of thermoplastic panels subjected to various impact energies. The first modeling method uses solid elements with a high-density mesh and a ply-by-ply modeling approach similar to previously published work for thermosets. This method has the capability of capturing individual crack development, progression, and delamination on a per ply basis. The second modeling method uses TSHELL elements that have in-plane dimensions that are an order of magnitude larger than the elements used in the solid element approach and reduces the number of elements through the thickness of the laminate. The second method produces a lower-fidelity model with reduced run times that is incapable of monitoring every delamination plane and damage within each ply. Results from both simulation methods are compared to experiment, and limitations of the methods are discussed.

Composite material↗

Progressive Damage and Failure Analysis of Thermoplastic Composites in Low Velocity Impact Using MAT299

As part of the NASA Hi-Rate Composite Aircraft Manufacturing (HiCAM) Project, state-of-the-art progressive damage and failure analysis (PDFA) tools developed for use with thermosets are being evaluated for use in modeling alternative material systems, like thermoplastics. Experimental low-velocity impact data of a thermoplastic material system, AS4D/PEKK-FC, is presented and includes characterization of the impact damage mechanisms as well as associated load and displacement data. Following the presentation of experimental results, two simulation approaches using the PDFA tool MAT299 in the commercial off-the-shelf finite element software LS-DYNA are employed to predict damage area and force-displacement responses of thermoplastic panels subjected to various impact energies. The first modeling method uses solid elements with a high-density mesh and a ply-by-ply modeling approach similar to previously published work for thermosets. This method has the capability of capturing individual crack development, progression, and delamination on a per ply basis. The second modeling method uses TSHELL elements that have in-plane dimensions that are an order of magnitude larger than the elements used in the solid element approach and reduces the number of elements through the thickness of the laminate. The second method produces a lower-fidelity model with reduced run times that is incapable of monitoring every delamination plane and damage within each ply. Results from both simulation methods are compared to experiment, and limitations of the methods are discussed.

Composite material↗

LS-DYNA User-Defined Internal Ballistic Modeling

- LS-DYNA Explicit Finite Element Analysis software and CADPROG Internal Ballistic Analysis code are integrated as a single modeling tool to analyze pyro-mechanical devices. - Combining these two codes allows the ballistic calculations to be performed without modeling the propellant in an FEA mesh. At each LS-DYNA time step, CADPROG is analytically run using the kinematic data (stroke, velocity, chamber volume) fed back from the LS-DYNA simulation. Calculated pressure is then applied to a piston or any applicable surface mesh in LS-DYNA model interactively. -All external loads such as friction, damping loads, assisting/resisting loads, locking/unlocking loads are modeled in LS-DYNA and coupled with pressure loads from CADPROG to create a fully defined equation of motion -Both codes are written in Fortran 77. CADPROG is inserted in LS-DYNA source code as a user-defined subroutine and re-compiled to generate a custom executable.

pyrotechnics↗

The CARMENES Search for Exoplanets Around M Dwarfs: Revisiting the GJ 581 Multi-Planetary System With New Doppler Measurements From CARMENES, HARPS, and HIRES

Context.GJ 581 is a nearby M dwarf known to host a packed multiple planet system composed of two super-Earths and a Neptune-mass planet. We present new orbital analyses of the GJ 581 system, utilizing recent radial velocity (RV) data obtained from the CARMENES spectrograph combined with newly reprocessed archival data from the HARPS and HIRES spectrographs. Aims.Our aim was to analyze the post-discovery spectroscopic data of GJ 581, which were obtained with CARMENES. In addition, we used publicly available HIRES and HARPS spectroscopic data to seek evidence of the known and disputed exoplanets in this system. We aimed to investigate the stellar activity of GJ 581 and update the planetary system’s orbital parameters using state-of-the-art numerical models and techniques. Methods.We performed a periodogram analysis of the available precise CARMENES, HIRES, and HARPS RVs and of stellar activity indicators. We conducted detailed orbital analyses by testing various orbital configurations consistent with the RV data. We studied the posterior probability distribution of the parameters fit to the data and we explored the long-term stability and overall orbital dynamics of the GJ 581 system. Results. We refined the orbital parameters of the GJ 581 system using the most precise and complete set of Doppler data available. Consistent with the existing literature, our analysis confirms that the system is unequivocally composed of only three planets detectable in the present data, dismissing the putative planet GJ 581 d as an artifact of stellar activity. Our N-body fit reveals that the system’s inclination is i=47.0+14.6−13.0deg, which implies that the planets could be up to 30% more massive than their previously reported minimum masses. Furthermore, we report that the GJ 581 system exhibits long-term stability, as indicated by the posterior probability distribution, characterized by secular dynamical interactions without the involvement of mean motion resonances.

Satellites↗

LS-DYNA User-Defined Internal Ballistic Modeling

LS-DYNA Explicit Finite Element Analysis software and CADPROG Internal Ballistic Analysis code are integrated as a single modeling tool to analyze pyro-mechanical devices. Coupling these two codes allows the ballistic calculations to be performed without modeling the propellant in an FEA mesh. At each LS-DYNA time step, CADPROG is run analytically using the kinematic data (stroke, velocity, chamber volume) fed back from the LS-DYNA simulation. The calculated pressure is then applied to a piston or any applicable surface mesh in LS-DYNA model interactively. All external loads such as friction, damping loads, assisting/resisting loads, locking/unlocking loads are modeled in LS-DYNA and coupled with pressure loads from CADPROG to create a fully defined equation of motion Both codes are written in Fortran 77. CADPROG is integrated in the LS-DYNA source code as a user-defined subroutine and recompiled to generate a custom executable.

pyrotechnics↗

Simulating photospheric Doppler velocity fields

A method is described for constructing artificial data that realistically simulate photospheric velocity fields. The velocity fields include rotation, differential rotation, meridional circulation, giant cell convection, supergranulation, convective limb shift, p-mode oscillations, and observer motion. Data constructed by this method can be used for testing algorithms designed to extract and analyze these velocity fields in real Doppler velocity data.

Hathaway, David H.↗

A Science-Focused Artificial Intelligence (AI) Responding in Real-Time to New Information: Capability Demonstration for Ocean World Missions

Introduction: Artificial intelligence (AI) has long been considered a potential mechanism to explore increasingly challenging environments, including those with extreme temperatures and pressures, limited communication capabilities, or those with demanding terrain. We posit that missions in extreme environments could deploy an onboard AI focused on science observations and goals in order to augment a traditional concept(s) of operations (ConOps). An onboard AI capability could perform functions such as data analysis in order to make high-level decisions, including prioritized data transmission for analysis by ground-based teams or autonomously-guided follow-on analyses that maximize science return. Such a capability would empower missions to respond to scientific data of interest in real-time; a mission could make observations and perform a preliminary analysis to alert ground-based scientists to an observation of interest, enabling an informed, rapid response from Earth-based teams. Enceladus Case Study for Onboard AI: We are developing an onboard AI capability for real-time telemetry response that formulates and carries-out informed decisions in service to established mission goals, enabling increased science return of a mission. We focus our AI development for use on a constellation of SmallSats orbiting Enceladus. Our Enceladus case study tests autonomous decision-making capabilities in scenarios with complex orbital dynamics, plume ejecta, extreme cold environments, power restrictions, and a requirement to maximize science return for a potential positive detection of life, while critically evaluating the potential for false positives. Telemetry includes simulated scientific data, spacecraft onboard operational data (e.g., position, velocity, and rotation), and engineering hardware performance data. Enceladus SmallSat Constellation. Our constellation includes eight SmallSat spacecraft in an 8:35 resonant orbit-based formation, leveraging Saturn’s gravitational forces to maintain stable orbits with global coverage around Enceladus. To our knowledge, we simulate the first stable configuration of multiple spacecraft in closed orbits around Enceladus, using a full ephemeris force model (Russell and Lara, 2009). Each spacecraft’s orbit will precess, causing an eastward ground track shift (from an orbiter’s perspective) of each spacecraft for each orbit. However, all spacecraft return to their original positions relative to Enceladus after eight Enceladus revolutions around Saturn. We model communication pathways between SmallSats to understand how information would need to be transmitted across the constellation to enable AI-driven decision-making and resource allocation across the fleet. Capability Demonstration. Our simulated capability demonstration inputs position, velocity, and rotation telemetry from our Enceladus-focused constellation simulations, and mass spectrometry data collected from abiotic and biotic laboratory-analog ocean world experiments (Theiling et al., 2018; Theiling, 2021; Da Poian et al., 2023). Data from these experiments are used to simulate MS measurements and different scenarios of science observations for onboard analysis performed on each of the eight spacecraft. For these demonstrations, we integrate 24 machine learning (ML) algorithms into an onboard intelligence as a ‘knowledge base’, including algorithms evaluating data quality and those predicting (with % confidence) gas composition, ocean aqueous chemistry, and whether the sample was influenced by microbial life. The onboard AI capability is designed to use the knowledge base to come to a consensus-based decision in the interpretation of the observed data in order to request additional action outside of a pre-defined ConOps. Requested actions could include e.g., prioritized downlink to Earth (for analysis by ground-based teams) or follow-on analyses performed across the constellation. The spacecraft’s intelligent onboard planner must then determine whether sufficient resources (e.g., time, power, etc.) are available and weigh the request with mission priorities. In our simulation, the constellation is able to identify potential biosignatures using onboard ML algorithms, evaluate the confidence of that prediction, and perform follow-on analyses across the fleet to confirm the detection, in order to best prepare a transmission of these data to Earth-based teams.

astrobiology↗

Exploratory Experiments to Probe the Effect of Bulk Density and Porosity on The Morphology and Ejecta Kinematics of Impact Craters

The morphometry of relatively small impact craters are influenced by the physical properties of the target. To investigate the control of bulk density and porosity on the crater-formation processing the gravity regime, we conducted a series of impact experiments, varying each these target parameters while holding the other constant. Three different sands were used to construct cohesionless targets: quartz (0.4-0.8 mm), garnet (0.425-1.0 mm), and alumina (0.297-0.71mm), representing a range of intrinsic grain densities from 2.65 to 4.02 g cm-3. High-porosity targets were constructed by carefully pouring the sand into the center of a cylindrical PVC target bucket (inner diameter 26.2 cm, height 12 cm) and allowing it to fill the bucket at the angle of repose before being leveled flat at the top of the bucket. Low-porosity targets were obtained by pluviation of the granular material through a 1 mm sieve that was set directly above the target bucket. With the disparate intrinsic densities of the sand in combination with the variations of the packing technique, we attained differences in the bulk-target density of up to 32%while keeping porosity constant. The impact experiments were conducted with the vertical gun in the Experimental Impact Laboratory at NASA Johnson Space Center; using 3/16” (4.76 mm) diameter aluminum projectiles launched at1.55 ± 0.03 km s-1. The ejecta were observed using the laser-based Ejection Velocity Measurement System, providing data on launch positions and velocities of ejected particles. Submillimeter topographic data of the resulting craters were collected after each experiment with a NextEngine 3D scanner. Regardless of target material or density, all craters exhibited a simple bowl shape, but a trend of increasing depth-diameter ratio with increasing target porosity is observed across the entire experimental suite. Despite these morphometric differences, ejecta launch angles and speeds remain remarkably similar amongst all of the target configurations.

impact cratering↗

Pre-Voyager velocities, accelerations and shrinkage rates of Jovian cloud features

Voyager I data provide detailed information on the latitudinal dependence of velocities in the Jovian atmosphere. In the present paper, pre-Voyager velocity data are summarized, and gross differences with the Voyager I results are revealed. Analytical expressions are derived for the shrinkage rates and acceleration of the Great Red Spot and white ovals (located at -23 degrees and -34 degrees latitude, respectively) for the period from 1943 to 1979.

Beebe, R. F.↗

A high speed data acquisition system for the analysis of velocity, density, and total temperature fluctuations at transonic speeds

The use of a high-speed Dynamic Data Acquisition System (DDAS) to measure simultaneously velocity, density, and total temperature fluctuations is described. The DDAS is used to automate the acquisition of hot-wire calibration data. The data acquisition, data handling, and data reporting techiques used by DDAS are described. Sample data are used to compare results obtained with the DDAS with those obtained from the FM tape and post-test digitization method.

Clukey, Steven J.↗

Thermocapillary convection in a liquid bridge

Results from experiments on thermocapillary flow in a vertical liquid bridge are reported. Data on surface velocities are presented for four different silicone oils at several values of the temperature difference across the liquid bridge and for three different average temperatures. Also, axial velocity measured as a function of radial position in the bridge is reported. A theoretical model of the velocity and temperature fields in the system is formulated and solved by finite differences. The experimental data on surface velocities are nondimensionalized, and are found to collapse on a single line when plotted against the Marangoni number. Scaled velocities are relatively insensitive to changes in the value of the Marangoni number from 20 to 290, and the Prandtl number from 1460 to 7120. The data are in reasonable accord with predictions from theory.

Mcneil, Thomas J.↗

Observations of mesoscale vertical velocities around frontal zones

Vertical velocity and reflectivity data obtained with a VHF Doppler radar over a 15-day period in October and November of 1981 are analyzed. Standard radiosonde data and surface observations were used to locate two occluded fronts, two warm fronts, and a cold front that passed the radar site. These fronts are also evident in the radar reflectivity data. Most studies of the vertical circulation patterns associated with mososcale systems have used precipitation and cloud formations as tracers. Unlike other observational techniques, the VHF radar permits the continuous measurement of the three-dimensional air velocity vector in time and height from a fixed location. With the beam in a vertically pointing position, signals are scattered from turbulent variations in the refractive index with half the scale of the radar wavelength and by regions with sudden changes in the refractive index associated with horizontally stratified layers. Generally, the strongest echoes occur at the maximum in the vertical gradient of refractivity, usually at the base of a temperature inversion, such as the tropopause. VHF radars can also be used to locate atmospheric fronts, which are characterized by static stability, large horizontal temperature gradients, large vorticities, and vertical wind shears. These radars can provide the velocity field data needed to study wave motions associated with fronts and compare the actual vertical circulation to theoretical predictions.

Dennis, T. S.↗