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NASA NTRS2012

Effect of Population III Multiplicity on Dark Star Formation

We numerically study the mutual interaction between dark matter (DM) and Population III (Pop III) stellar systems in order to explore the possibility of Pop III dark stars within this physical scenario. We perform a cosmological simulation, initialized at z approx. 100, which follows the evolution of gas and DM. We analyze the formation of the first mini halo at z approx. 20 and the subsequent collapse of the gas to densities of 10(exp 12)/cu cm. We then use this simulation to initialize a set of smaller-scale 'cut-out' simulations in which we further refine the DM to have spatial resolution similar to that of the gas. We test multiple DM density profiles, and we employ the sink particle method to represent the accreting star-forming region. We find that, for a range of DM configurations, the motion of the Pop III star-disk system serves to separate the positions of the protostars with respect to the DM density peak, such that there is insufficient DM to influence the formation and evolution of the protostars for more than approx. 5000 years. In addition, the star-disk system causes gravitational scattering of the central DM to lower densities, further decreasing the influence of DM over time. Any DM-powered phase of Pop III stars will thus be very short-lived for the typical multiple system, and DM will not serve to significantly prolong the life of Pop III stars.

Stacy, Athena↗

NASA NTRS2020

A Fast Evaluation of PDA Experimental Parameters Using Mie Scattering to Enhance the Measurement Accuracy of Droplet Size Distributions

The Phase Doppler technique (PDA) and its implementation generally relies on a geometric optics formulation for light scattering to estimate drop sizes from the measured phase differences between Doppler signals from two or more detectors. Although this limits experimental PDA scattering geometries to those where only one component of the geometric scatter is dominant, the calculations are relatively simple. This TM describes a fast method to evaluate PDA experimental parameters analytically using Mie scattering that provides a performance estimate of all possible configurations. The best configurations are fully tested using a Monte Carlo simulation to obtain a more accurate capability estimate for each one.

PDA↗

NASA NTRS2021

High Temperature Solid Particle Erosion in a Melt-Infiltrated SiC/SiC Ceramic Matrix Composite

Ceramic matrix composites (CMCs) are an enabling propulsion material system that offer weight benefits over current Ni-based superalloys, and have higher temperature capabilities that can reduce cooling requirements. Incorporating CMCs into the hot section of gas-turbine engines therefore leads to an increase in engine efficiency. While significant advancements have been made, challenges still remain for current and next-generation gas-turbines; particularly when operating in dust-laden or erosive environments. Solid particles entrained in the gas flow can impact engine hardware resulting in localized damage and material removal due to repeated, cumulative impacts. In this study, the erosion behavior of a melt-infiltrated (MI) silicon carbide fiber-reinforced silicon carbide (SiC/SiC) CMC is investigated at high temperature (1,200 °C) in a simulated combustion environment using 150 µm alumina particles as erodent. Particle impact velocities ranged from 100 to 200 m/s and the angle of impingement varied from 30° to 90°. Erosion testing was also performed on α-SiC to elucidate similarities and differences in the erosion response of the composite compared to that of a monolithic ceramic. Scanning electron microscopy (SEM) was used to study the post-erosion damage morphology and the governing mechanisms of material removal.

Ceramic matrix composites (CMCs), solid particle e↗

NASA NTRS2001

Evaluation of The Performance of The Mars Environmental Compatibility Assessment Electrometer

The Mars Environmental Compatibility Assessment (MECA) electrometer is an instrument that was designed jointly by researchers at the Jet Propulsion Laboratory and the Kennedy Space Center, and is intended to fly on a future space exploration mission of the surface of Mars. The electrometer was designed primarily to study (1) the electrostatic interaction between the Martian soil and five different types of insulators, which are attached to the electrometer, as the electrometer is rubbed over the Martian soil. The MECA/Electrometer is also capable of measuring (2) the presence of charged particles in the Martian atmosphere, (3) the local electric field strength, and (4) the local temperature. The goal of the research project described in this report was to test and evaluate the measurement capabilities of the MECA/Electrometer under simulated Martian surface conditions using facilities located in the Labs and Testbeds Division at the Kennedy Space Center. The results of this study indicate that the Martian soil simulant can triboelectrically charge up the insulator surface. However, the maximum charge buildup did not exceed 18% of the electrometer's full-range sensitivity when rubbed vigorously, and is more likely to be as low as 1% of the maximum range when rubbed through soil. This indicates that the overall gain of the MECA/Electrometer could be increased by a factor of 50 if measurements at the 50% level of full-range sensitivity are desired. The ion gauge, which detects the presence of charged particles, was also evaluated over a pressure range from 10 to 400 Torr (13 to 533 mbar). The electric field sensor was also evaluated. Although the temperature sensor was not evaluated due to project time constraints, it was previously reported to work properly.

Mantovani, James G.↗

NASA NTRS2002

Evaluation of the Performance of the Mars Environmental Compatibility Assessment Electrometer

Mantovani, James G.↗

NASA NTRS1989

Mechanical properties of lunar regolith and lunar soil simulant

Through the Surveyor 3 and 7, and Apollo 11-17 missions a knowledge of the mechanical properties of Lunar regolith were gained. These properties, including material cohesion, friction, in-situ density, grain-size distribution and shape, and porosity, were determined by indirect means of trenching, penetration, and vane shear testing. Several of these properties were shown to be significantly different from those of terrestrial soils, such as an interlocking cohesion and tensile strength formed in the absence of moisture and particle cementation. To characterize the strength and deformation properties of Lunar regolith experiments have been conducted on a lunar soil simulant at various initial densities, fabric arrangements, and composition. These experiments included conventional triaxial compression and extension, direct tension, and combined tension-shear. Experiments have been conducted at low levels of effective confining stress. External conditions such as membrane induced confining stresses, end platten friction and material self weight have been shown to have a dramatic effect on the strength properties at low levels of confining stress. The solution has been to treat these external conditions and the specimen as a full-fledged boundary value problem rather than the idealized elemental cube of mechanics. Centrifuge modeling allows for the study of Lunar soil-structure interaction problems. In recent years centrifuge modeling has become an important tool for modeling processes that are dominated by gravity and for verifying analysis procedures and studying deformation and failure modes. Centrifuge modeling is well established for terrestrial enginering and applies equally as well to Lunar engineering. A brief review of the experiments is presented in graphic and outline form.

Steven W Perkins↗

NASA NTRS2011

Validation and Simulation of Ares I Scale Model Acoustic Test - 3 - Modeling and Evaluating the Effect of Rainbird Water Deluge Inclusion

The Ares I Scale Model Acoustics Test (ASMAT) is a series of live-fire tests of scaled rocket motors meant to simulate the conditions of the Ares I launch configuration. These tests have provided a well documented set of high fidelity measurements useful for validation including data taken over a range of test conditions and containing phenomena like Ignition Over-Pressure and water suppression of acoustics. Building on dry simulations of the ASMAT tests with the vehicle at 5 ft. elevation (100 ft. real vehicle elevation), wet simulations of the ASMAT test setup have been performed using the Loci/CHEM computational fluid dynamics software to explore the effect of rainbird water suppression inclusion on the launch platform deck. Two-phase water simulation has been performed using an energy and mass coupled lagrangian particle system module where liquid phase emissions are segregated into clouds of virtual particles and gas phase mass transfer is accomplished through simple Weber number controlled breakup and boiling models. Comparisons have been performed to the dry 5 ft. elevation cases, using configurations with and without launch mounts. These cases have been used to explore the interaction between rainbird spray patterns and launch mount geometry and evaluate the acoustic sound pressure level knockdown achieved through above-deck rainbird deluge inclusion. This comparison has been anchored with validation from live-fire test data which showed a reduction in rainbird effectiveness with the presence of a launch mount.

Strutzenberg, Louise L.↗

NASA NTRS1993

Design and testing of a unique randomized gravity, continuous flow bioreactor

A rotating, null gravity simulator, or Couette bioreactor was successfully used for the culture of mammalian cells in a simulated microgravity environment. Two limited studies using Lipomyces starkeyi and Streptomyces clavuligerus were also conducted under conditions of simulated weightlessness. Although these studies with microorganisms showed promising preliminary results, oxygen limitations presented significant limitations in studying the biochemical and cultural characteristics of these cell types. Microbial cell systems such as bacteria and yeast promise significant potential as investigative models to study the effects of microgravity on membrane transport, as well as substrate induction of inactive enzyme systems. Additionally, the smaller size of the microorganisms should further reduce the gravity induced oscillatory particle motion and thereby improve the microgravity simulation on earth. Focus is on the unique conceptual design, and subsequent development of a rotating bioreactor that is compatible with the culture and investigation of microgravity effects on microbial systems. The new reactor design will allow testing of highly aerobic cell types under simulated microgravity conditions. The described reactor affords a mechanism for investigating the long term effects of reduced gravity on cellular respiration, membrane transfer, ion exchange, and substrate conversions. It offers the capability of dynamically altering nutrients, oxygenation, pH, carbon dioxide, and substrate concentration without disturbing the microgravity simulation, or Couette flow, of the reactor. All progeny of the original cell inoculum may be acclimated to the simulated microgravity in the absence of a substrate or nutrient. The reactor has the promise of allowing scientists to probe the long term effects of weightlessness on cell interactions in plants, bacteria, yeast, and fungi. The reactor is designed to have a flow field growth chamber with uniform shear stress, yet transfer high concentrations of oxygen into the culture medium. The system described allows for continuous, on line sampling for production of product without disturbing fluid and particle dynamics in the reaction chamber. It provides for the introduction of substrate, or control substances after cell adaptation to simulated microgravity has been accomplished. The reactor system provides for the nondisruptive, continuous flow replacement of nutrient and removal of product. On line monitoring and control of growth conditions such as pH and nutrient status are provided. A rotating distribution valve allows cessation of growth chamber rotation, thereby preserving the simulated microgravity conditions over longer periods of time.

Lassiter, Carroll B.↗

NASA NTRS1985

Numerical techniques for large cosmological N-body simulations

Techniques for carrying out large N-body simulations of the gravitational evolution of clustering in the fundamental cube of an infinite periodic universe are described and compared. The accuracy of the forces derived from several commonly used particle mesh schemes is examined, showing how submesh resolution can be achieved by including short-range forces between particles by direct summation techniques. The time integration of the equations of motion is discussed, and the accuracy of the codes for various choices of 'time' variable and time step is tested by considering energy conservation as well as by direct analysis of particle trajectories. Methods for generating initial particle positions and velocities corresponding to a growing mode representation of a specified power spectrum of linear density fluctuations are described. The effects of force resolution are studied and different simulation schemes are compared. An algorithm is implemented for generating initial conditions by varying the number of particles, the initial amplitude of density fluctuations, and the initial peculiar velocity field.

Efstathiou, G.↗

NASA NTRS1987

Evidence for cyclotron maser emission from the sun and stars

Recent observational and theoretical work on cyclotron maser instability is reviewed, with emphasis on the similarities between microwave spike bursts from the sun and bursts from stars and planets. Results on particle-in-cell simulations are discussed, and it is suggested that such studies may provide further information on the amount and efficiency of energy transfer by the maser radiation. Observational tests of the cyclotron maser theory are considered, in addition to the role of the cyclotron maser as an energy transport mechanism in solar flares.

Dulk, G. A.↗

NASA NTRS1988

Computer modeling of test particle acceleration at oblique shocks

The present evaluation of the basic techniques and illustrative results of charged particle-modeling numerical codes suitable for particle acceleration at oblique, fast-mode collisionless shocks emphasizes the treatment of ions as test particles, calculating particle dynamics through numerical integration along exact phase-space orbits. Attention is given to the acceleration of particles at planar, infinitessimally thin shocks, as well as to plasma simulations in which low-energy ions are injected and accelerated at quasi-perpendicular shocks with internal structure.

Decker, Robert B.↗

NASA NTRS1989

Effects of ionizing radiation on cryogenic infrared detectors

The Diffuse Infrared Background Experiment (DIRBE) is one of three experiments to be carried aboard the Cosmic Background Explorer (COBE) satellite scheduled to be launched by NASA on a Delta rocket in 1989. The DIRBE is a cryogenic absolute photometer operating in a liquid helium dewar at 1.5 K. Photometric stability is a principal requirement for achieving the scientific objectives of this experiment. The Infrared Astronomy Satellite (IRAS), launched in 1983, which used detectors similar to those in DIRBE, revealed substantial changes in detector responsivity following exposure to ionizing radiation encountered on passage through the South Atlantic Anomaly (SAA). Since the COBE will use the same 900 Km sun-synchronous orbit as IRAS, ionizing radiation-induced performance changes in the detectors were a major concern. Here, ionizing radiation tests carried out on all the DIRBE photodetectors are reported. Responsivity changes following exposure to gamma rays, protons, and alpha particle are discussed. The detector performance was monitored following a simulated entire mission life dose. In addition, the response of the detectors to individual particle interactions was measured. The InSb photovoltaic detectors and the Blocked Impurity Band (BIB) detectors revealed no significant change in responsivity following radiation exposure. The Ge:Ga detectors show large effects which were greatly reduced by proper thermal annealing.

Moseley, S. H.↗

NASA NTRS1990

Development of impact design methods for ceramic gas turbine components

Impact damage prediction methods are being developed to aid in the design of ceramic gas turbine engine components with improved impact resistance. Two impact damage modes were characterized: local, near the impact site, and structural, usually fast fracture away from the impact site. Local damage to Si3N4 impacted by Si3N4 spherical projectiles consists of ring and/or radial cracks around the impact point. In a mechanistic model being developed, impact damage is characterized as microcrack nucleation and propagation. The extent of damage is measured as volume fraction of microcracks. Model capability is demonstrated by simulating late impact tests. Structural failure is caused by tensile stress during impact exceeding material strength. The EPIC3 code was successfully used to predict blade structural failures in different size particle impacts on radial and axial blades.

Song, J.↗

NASA NTRS1996

Unsteady Simulation of the Viscous Flow About a V-22 Rotor and Wing in Hover

Results of an unsteady thin-layer Navier-Stokes simulation of a 0.658-scale V-22 rotor and wing configuration in hover are presented. All geometric components of the flapped-wing and rotor test rig, including rotor blades, are accurately modeled. Rotor motion and rotor/airframe interference effects are simulated directly using moving body overset grid methods. Tiltrotor hover aerodynamics are visualized via unsteady particle trace images. Wing download predictive ability is demonstrated. Simulation results are compared with experimental data.

Meakin, Robert L.↗

NASA NTRS2009

Navier-Stokes Simulation of a Heavy Lift Slowed-Rotor Compound Helicopter Configuration

Time accurate numerical simulations were performed using the Reynolds-averaged Navier-Stokes (RANS) flow solver OVERFLOW for a heavy lift, slowed-rotor, compound helicopter configuration, tested at the NASA Langley 14- by 22-Foot Subsonic Tunnel. The primary purpose of these simulations is to provide support for the development of a large field of view Particle Imaging Velocimetry (PIV) flow measurement technique supported by the Subsonic Rotary Wing (SRW) project under the NASA Fundamental Aeronautics program. These simulations provide a better understanding of the rotor and body wake flows and helped to define PIV measurement locations as well as requirements for validation of flow solver codes. The large field PIV system can measure the three-dimensional velocity flow field in a 0.914m by 1.83m plane. PIV measurements were performed upstream and downstream of the vertical tail section and are compared to simulation results. The simulations are also used to better understand the tunnel wall and body/rotor support effects by comparing simulations with and without tunnel floor/ceiling walls and supports. Comparisons are also made to the experimental force and moment data for the body and rotor.

Allan, Brian G.↗

NASA NTRS2014

Induction Heating of Hypervelocity Impact Samples to 2500 Degrees Centigrade

The Remote Hypervelocity Test Laboratory (RHTL) at White Sands Test Facility (WSTF) was asked to heat samples up to 2500 degrees Centigrade (4532 degrees Fahrenheit) to simulate reentry scenarios of crafts where heated shields are impacted with single small particles ranging from 0.2 to 1.0 millimeters (.008 to.039 inches) of various materials. The team decided an electromagnetic induction (induction heater) was the best method to achieve and control the temperatures in a rapid manner. The samples consisted of three-dimensional carbon-carbon and two-dimensional carbon-phenolic, which are both electrically conductive. After several attempts the team was able to achieve over 2500 degrees Centigrade (4532 degrees Fahrenheit) in ambient atmosphere. When the system was moved to the target chamber and the vacuum system evacuated down to 250 millitorr, arcing occurred between the bus bars and tank, the feedthrough fittings that carried the coolant and current, and between the target sample and coil. To overcome this arcing, conformal coatings, room temperature vulcanization (RTV) silicone, and other non-conductive materials were used to isolate the electromagnetic fields.

Simmons, Joshua↗

NASA NTRSDate not supplied

Coupling a Particle Trajectory Capability to the US3D CFD Flow Solver

The purpose of the current research effort is to incorporate particle trajectory equations into the US3D CFD flow solver. The integrated code will allow higher-fidelity modeling of particle-fluid interactions and allow for the simulation of physical effects such as surface heating augmentation due to particle impacts. The key elements underpinning the current work are a robust tracking algorithm that can identify the encompassing mesh elements for individual particles and a point to point MPI frame-work. These developments combined with accurate property models and high-order time-stepping deliver realistic simulations on larger computational grids for a wide range of particle mass loadings. The coupled US3D-particle code will be applied to the Schiarparelli capsule and Earth-based experimental test cases.

A Sahai↗

NASA NTRS2023

The 17 April 2021 Widespread Solar Energetic Particle Event

A complex and long-lasting solar eruption on 17 April 2021 produced a widespread solar energetic particle (SEP) event that was observed by five longitudinally well-separated observers in the inner heliosphere that covered distances to the Sun from 0.42 to 1 au: BepiColombo, Parker Solar Probe, Solar Orbiter, STEREO A, and near-Earth spacecraft. The event was the second widespread SEP event detected in solar cycle 25, and it produced relativistic electrons and protons. It was associated with a long-lasting solar hard X-ray flare that showed multiple hard X-ray peaks over a duration of one hour. The event was further accompanied by a medium-fast coronal mass ejection (CME) with a speed of 880 km s -1 that drove a shock, an extreme ultraviolet wave, and long-lasting and complex radio burst activity that showed four distinct type III burst groups over a period of 40 min. We aim to understand the reason for the wide spread of elevated SEP intensities in the inner heliosphere as well as identify the underlying source regions of the observed energetic electrons and protons. We applied a comprehensive multi-spacecraft analysis of remote-sensing observations and in situ measurements of the energetic particles and interplanetary context to attribute the SEP observations at the different locations to the various potential source regions at the Sun. We used an ENLIL simulation to characterize the complex interplanetary state and its role in the energetic particle transport. The magnetic connection between each spacecraft and the Sun was determined using ballistic backmapping in combination with potential field source surface extrapolations in the lower corona. Using also a reconstruction of the coronal shock front, we then determined the times when the shock establishes magnetic connections with the different observers. Radio observations were used to characterize the directivity of the four main injection episodes, which were then employed in a 2D SEP transport simulation to test the importance of these different injection episodes. A comprehensive timing analysis of the inferred solar injection times of the SEPs observed at each spacecraft suggests different source processes being important for the electron and proton events. Comparison among the characteristics and timing of the potential particle sources, such as the CME-driven shock or the flare, suggests a stronger shock contribution for the proton event and a more likely flare-related source for the electron event. In contrast to earlier studies on widespread SEP events, we find that in this event an important ingredient for the wide SEP spread was the wide longitudinal range of about 110 o covered by distinct SEP injections, which is also supported by our SEP transport modeling.

sun↗