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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Impact ejecta dynamics in an atmosphere - Experimental results and extrapolations

It is noted that the impacts of 0.635-cm aluminum projectiles at 6 km/sec into fine pumice dust, at 1 atm, generate a ball of ionized gas behind an expanding curtain of upward moving ejecta. The gas ball forms a toroid which dissolves as it is driven along the interior of the ejecta curtain, by contrast to near-surface explosions in which a fireball envelops early-time crater growth. High frame rate Schlieren photographs show that the atmosphere at the base of the ejecta curtain is initially turbulent, but later forms a vortex. These experiments suggest that although small size ejecta may be decelerated by air drag, they are not simply lofted and suspended but become incorporated in an ejecta cloud that is controlled by air flow which is produced by the response of the atmosphere to the impact. The extrapolation of these results to large body impacts on the earth suggests such contrasts with laboratory experiments as a large quantity of impact-generated vapor, the supersonic advance of the ejecta curtain, the lessened effect of air drag due to the tenuous upper atmosphere, and the role of secondary cratering.

Schultz, P. H.↗
NASA NTRS1982

Dynamic effects of combustion

The dynamic effects of combustion are due to the evolution of exothermic energy and its deposition in the compressible medium where the process takes place. The paper examines the dynamics of combustion phenomena, including ignition, turbulent flame propagation (inflammation), explosion, and detonation, with emphasis on their exothermic characteristics. Ignition and explosion are treated as problems of nonlinear mechanics, and their dynamic behavior is described in terms of phase space models and cinematographic laser shear interferograms. The results of a numerical random vortex model of turbulent flame propagation are confirmed in a combustion tunnel experiment, where it was observed that a fresh mixture of burnt and unburnt gases can sustain combustion with a relatively small expenditure of overall mass flow, due to the increasing specific volume of burnt gases inside the flame front. An isentropic pressure wave is found to precede the accelerating flame in the process of detonation, and components of this presssure wave are shown to propagate at local sonic velocities.

Oppenheim, A. K.↗
NASA NTRS1992

Approximation methods for stochastic petri nets

Stochastic Marked Graphs are a concurrent decision free formalism provided with a powerful synchronization mechanism generalizing conventional Fork Join Queueing Networks. In some particular cases the analysis of the throughput can be done analytically. Otherwise the analysis suffers from the classical state explosion problem. Embedded in the divide and conquer paradigm, approximation techniques are introduced for the analysis of stochastic marked graphs and Macroplace/Macrotransition-nets (MPMT-nets), a new subclass introduced herein. MPMT-nets are a subclass of Petri nets that allow limited choice, concurrency and sharing of resources. The modeling power of MPMT is much larger than that of marked graphs, e.g., MPMT-nets can model manufacturing flow lines with unreliable machines and dataflow graphs where choice and synchronization occur. The basic idea leads to the notion of a cut to split the original net system into two subnets. The cuts lead to two aggregated net systems where one of the subnets is reduced to a single transition. A further reduction leads to a basic skeleton. The generalization of the idea leads to multiple cuts, where single cuts can be applied recursively leading to a hierarchical decomposition. Based on the decomposition, a response time approximation technique for the performance analysis is introduced. Also, delay equivalence, which has previously been introduced in the context of marked graphs by Woodside et al., Marie's method and flow equivalent aggregation are applied to the aggregated net systems. The experimental results show that response time approximation converges quickly and shows reasonable accuracy in most cases. The convergence of Marie's method and flow equivalent aggregation are applied to the aggregated net systems. The experimental results show that response time approximation converges quickly and shows reasonable accuracy in most cases. The convergence of Marie's is slower, but the accuracy is generally better. Delay equivalence often fails to converge, while flow equivalent aggregation can lead to potentially bad results if a strong dependence of the mean completion time on the interarrival process exists.

Jungnitz, Hauke Joerg↗
NASA NTRS1986

Electric field measurements during the Condor critical velocity experiment

The instrumentation of the Condor critical velocity Ba experiment (Wescott et al., 1986) for the measurements of the energetic particles and the electric field associated with a Ba explosion is described. The Ba explosion created a complex electric field pulse detected in situ by a single-axis double electric-field probe on a separate spacecraft. The measurements provide evidence of several important links in the critical-velocity chain, and are consistent with two hypotheses. The first hypothesis involves the creation of large polarization electric field due to charge separation; the second hypothesis implies a polarization of the beam by currents flowing across it. The chain of physical processes inferred from the observations is in agreement with most theories for the Alfven process.

Kelley, M. C.↗
NASA NTRS1992

On the nonlinear three dimensional instability of Stokes layers and other shear layers to pairs of oblique waves

The nonlinear evolution of a pair of initially oblique waves in a high Reynolds Number Stokes layer is studied. Attention is focused on times when disturbances of amplitude epsilon have O(epsilon(exp 1/3)R) growth rates, where R is the Reynolds number. The development of a pair of oblique waves is then controlled by nonlinear critical-layer effects. Viscous effects are included by studying the distinguished scaling epsilon = O(R(exp -1)). This leads to a complicated modification of the kernel function in the integro-differential amplitude equation. When viscosity is not too large, solutions to the amplitude equation develop a finite-time singularity, indicating that an explosive growth can be introduced by nonlinear effects; we suggest that such explosive growth can lead to the bursts observed in experiments. Increasing the importance of viscosity generally delays the occurrence of the finite-time singularity, and sufficiently large viscosity may lead to the disturbance decaying exponentially. For the special case when the streamwise and spanwise wavenumbers are equal, the solution can evolve into a periodic oscillation. A link between the unsteady critical-layer approach to high-Reynolds-number flow instability, and the wave vortex approach is identified.

Wu, Xuesong↗
DOE OSTI2022

Shock wave formation from head-on collision of two subsonic vortex rings

Vortex ring collisions have attracted intense interest in both water and air studies (Baird in Proc R Soc Lond Ser Math Phys Sci 409:59–65, 1987, Poudel et al. in Phys Fluids 33:096105, 2021, Lim and Nickels in Nature 357:225, 1992, New et al. in Exp Fluids 57:109, 2016, Suzuki et al. in Geophys Res Lett 34, 2007, Yan et al. in J Fluids Eng 140:054502, 2018, New et al. in J Fluid Mech 899, 2020, Cheng et al. in Phys Fluids 31:067107, 2019, Hernández and Reyes in 29:103604, 2017, Mishra et al. in Phys Rev Fluids, 2021, Zednikova et al. in Chem Eng Technol 42:843–850, 2019, Kwon et al. in Nature 600:64–69, 2021). These toroidal structures spin around a central axis and travel in the original direction of impulse while spinning around the core until inertial forces become predominant causing the vortex flow to spontaneously decay to turbulence (Vortex Rings, https://projects.iq.harvard.edu/smrlab/vortex-rings). Previous studies have shown the collision of subsonic vortex rings resulting in reconnected vortex rings, but the production of a shock wave from the collision has not been demonstrated visibly (Lim and Nickels in Nature 357:225, 1992, Cheng et al. in Phys Fluids 31:067107, 2019). Here we present the formation of a shock wave due to the collision of explosively formed subsonic vortex rings. As the vortex rings travel at Mach 0.66 toward the collision point, they begin to trap high pressure air between them. Upon collision, high pressure air was imploded and released radially away from the axis of the collision, generating a visible shock wave traveling through and away from the colliding vortices at Mach 1.22. Our results demonstrate a pressure gradient with high pressure release creating a shock wave. We anticipate our study to be a starting point for more explosively formed vortex collisions. For example, explosives with different velocities of detonation could be tested to produce vortex rings of varying velocities.

42 ENGINEERING↗
DOE OSTI2022

Developing solid-surface plasma facing components for pilot plants and reactors with replenishable wall claddings and continuous surface conditioning. Part A: concepts and questions

Abstract It is estimated that pilot plants and reactors may experience rates of net erosion and deposition of solid plasma facing component (PFC) material of 10 3 –10 5 kg yr −1 . Even if the net erosion (wear) problem can be solved, the redeposition of so much material has the potential for major interference with operation, including disruptions due to so-called ‘unidentified flying objects (UFOs)’ and unsafe dust levels. The potential implications appear to be no less serious than for plasma contact with the divertor target: a dust explosion or a major UFO-disruption could be as damaging for an actively-cooled deuterium-tritium (DT) tokamak as target failure. It will therefore be necessary to manage material deposits to prevent their fouling operation. This situation appears to require a fundamental paradigm shift with regard to meeting the challenge of taming the plasma–material interface: it appears that any acceptable solid PFC material will in effect be flow-through , like liquid–metal PFCs, although at far lower mass flow rates. Solid PFC material will have to be treated as a consumable , like brake pads in cars. ITER will use high-Z (tungsten) armor on the divertor targets and low-Z (beryllium) on the main walls. The ARIES-AT reactor design calls for a similar arrangement, but with SiC cladding on the main walls. Non-metallic low-Z refractory materials such as ceramics (graphite, SiC, etc) used as in situ replenishable, relatively thin—of order mm—claddings on a substrate which is resistant to neutron damage could provide a potential solution for the main walls, while reducing the risk of degrading the confined plasma. Separately, wall conditioning has proven essential for achieving high performance. For DT devices, however, standard methods appear to be unworkable, but recently powder droppers injecting low-Z material ∼continuously into discharges have been quite effective and may be usable in DT devices as well. The resulting massive generation of low-Z debris, however, has the same potential to seriously disrupt operation as noted above. Powder droppers provide a unique opportunity to carry out controlled studies on the management of low-Z slag in all current tokamaks, independent of whether their protection tiles use low-Z or high-Z material.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Experimental Investigation of Uranium Volatility during Vapor Condensation

The predictive models that describe the fate and transport of radioactive materials in the atmosphere following a nuclear incident (explosion or reactor accident) assume that uranium-bearing particulates would attain chemical equilibrium during vapor condensation. Here, we show that kinetically driven processes in a system of rapidly decreasing temperature can result in substantial deviations from chemical equilibrium. This can cause uranium to condense out in oxidation states (e.g., UO 3 vs UO 2 ) that have different vapor pressures, significantly affecting uranium transport. To demonstrate this, we synthesized uranium oxide nanoparticles using a flow reactor under controlled conditions of temperature, pressure, and oxygen concentration. The atomized chemical reactants passing through an inductively coupled plasma cool from ~5000 to 1000 K within milliseconds and form nanoparticles inside a flow reactor. The ex situ analysis of particulates by transmission electron microscopy revealed 2–10 nm crystallites of fcc-UO 2 or α-UO 3 depending on the amount of oxygen in the system. α-UO 3 is the least thermodynamically preferred polymorph of UO 3 . The absence of stable uranium oxides with intermediate stoichiometries (e.g., U 3 O 8 ) and sensitivity of the uranium oxidation states to local redox conditions highlight the importance of in situ measurements at high temperatures. Therefore, we developed a laser-based diagnostic to detect uranium oxide particles as they are formed inside the flow reactor. Our in situ measurements allowed us to quantify the changes in the number densities of the uranium oxide nanoparticles (e.g., UO 3 ) as a function of oxygen gas concentration. Our results indicate that uranium can prefer to be in metastable crystal forms (i.e., α-UO 3 ) that have higher vapor pressures than the refractory form (i.e., UO 2 ) depending on the oxygen abundance in the surrounding environment. This demonstrates that the equilibrium processes may not dominate during rapid condensation processes, and thus kinetic models are required to fully describe uranium transport subsequent to nuclear incidents.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRSDate not supplied

Planning Satellite Swarm Measurements for Climate Models: Comparing Dynamic Constraint Processing and MILP Methods

We present D-SHIELD, a challenging climate science application to plan coordinated measurements (observations) for a constellation of satellites, each containing two different sensors, each with 61 pointing angle options. The L-band and P-band radar sensors collect data fed into a soil moisture model which tracks and predicts soil moisture across 1.67 million Ground Positions (GP). Soil moisture is an important predictor of wildfires, and then a predictor of floods, landslides and debris flow after a fire. Each measurement covers multiple GP due to the sensor footprint. Each GP has a "model error" which represents the uncertainty of the the soil moisture state prediction. Model error changes at different rates for each GP as the time since last observation increases and after significant events like rain. The planner's goal is to select measurements which maximize soil moisture model improvement (reduce model uncertainty). This problem is combinatorically explosive, involving many degrees of freedom for planner choices. Good domain heuristics can find solutions within a reasonable time for our application needs but cannot be proven optimal. In this paper we compare two different planning approaches to this problem: Dynamic Constraint Processing (DCP) and Mixed Integer Linear Programming (MILP). We match inputs and metrics for both DCP and MILP algorithms to enable a direct apples-to-apples comparison. We demonstrate and discuss the trades between DCP flexibility and performance vs. MILP's promise of provable optimality.

Rich Levinson↗
NASA NTRS1985

Buoyancy Effects upon Vapor Flame and Explosion Processes

The objective of this microgravity project is to develop an experimental and theoretical analyses critical to the understanding of the coupling of buoyancy and turbulence generation and its effect on fuel-air mixing, flame intensity and flame propagation in jet diffusion flames. The experiment is designed to examine certain effects of buoyancy acting on a diffusion flame in which the flame is directed either upward or downward. This change from negative to positive g is observed to significantly alter the flame shape although all other operating conditions are the same for both configurations. However, to perform this experiment a significant coaxial secondary air flow is needed in order to prevent flow reversal when the flame is inverted. The theoretical analysis that has been developed handles the secondary air flow and the extreme change in gravity vector direction. Thus the data will provide a measure of credibility of the analysis which will then be used to assist in the design of the actual zero-g experiment.

Edelman, R. B.↗
NASA NTRS1975

Nonlinear hyperbolic theory of thermal waves in metals

A closed-form solution for cylindrical thermal waves in metals is given based on the nonlinear hyperbolic system of energy-conservation and heat-flux relaxation equations. It is shown that heat released from a line source propagates radially outward with finite speed in the form of a thermal wave which exhibits a discontinuous wave front. Unique nonlinear thermal-wave solutions exist up to a critical amount of driving energy, i.e., for larger energy releases, the thermal flow becomes multivalued (occurrence of shock waves). By comparison, it is demonstrated that the parabolic thermal-wave theory gives, in general, a misleading picture of the profile and propagation of thermal waves and leads to physical (infinite speed of heat propagation) and mathematical (divergent energy integrals) difficulties. Attention is drawn to the importance of temporal heat-flux relaxation for the physical understanding of fast transient processes such as thermal waves and more general explosions and implosions.

Wilhelm, H. E.↗
NASA NTRSDate not supplied

Plasmoids, Flows, and Jets During Magnetic Reconnection in a Failed Filament Eruption

We report a detailed analysis of a flare/failed eruption in Active Region 12018 on April 3, 2014, using observations from SDO/AIA, IRIS, STEREO and Hinode/SOT. Initially, we observed multiple jets originating from the cusp of a large coronal bright point (null-point topology) 1-2 hours prior to the slow rise of a filament. The subsequent filament eruption, which was outside the IRIS field of view, was accompanied by a flare but remained confined. Multiple blobs were observed, most likely formed in a breakout current sheet near the cusp during the filament slow rise. During the explosive flare reconnection phase, plasmoids also appeared and moved bidirectionally (speed=100-285 km/s, periodicity~70 s) in the flare current sheet below the erupting filament. The tiny jet-like features in the fan loops were detected during the filament slow-rise/pre-flare phase associated with slow interchange/breakout reconnection at 3D null followed by multiple plasmoids moving along the fan-loops/separatrix. We will discuss why our interpretation is more robust than the nanoflare heating/flows suggested by Antolin et al. (2021).

P. Kumar↗
NASA NTRS1974

Explosive-actuated valve design concept that eliminates blow-by

A method of evaluating the normally open normally closed, explosive actuated valves that were selected for use in the trajectory correction propulsion subsystem of the Thermoelectric Outer Planet Spacecraft (TOPS) program is presented. The design philosophy which determined the requirements for highly reliable valves that could provide the performance capability during long duration (10 year) missions to the outer planets is discussed. The techniques that were used to fabricate the valves and manifold ten valves into an assembly with the capability of five propellant-flow initiation/isolation sequences are described. The test program, which was conducted to verify valve design requirements, is outlined and the more significant results are shown.

Hagler, R., Jr.↗
NASA NTRS1984

The 19 March 1982 Eruption and Lahar at Mount Saint Helens: Implications for Martian Outlfow Channels?

A small explosive eruption of Mount St. Helens set into motion an unusually complex series of geomorphic and hydrologic processes that had not previously been described in the literature. This event was unusual in that a laterally-directed eruption dislodged and mobilized a thick snowpack from the surrounding crater floor and walls, resulting in the formation of a temporary lake. Catastrophic release of this self-impounded lake spawned a series of destructive debris avalanches and debris flows that moved rapidly down the volcano's north flank and into the North Toutle River valley. Catastrophic release of volatiles mobilized by volcanic activity has been discussed as a possible mechanism to explain a class of outflow channels on Mars. The eruption of Mount St. Helens provides a unique opportunity to study the deposits and landforms created by such an event; a more detailed field study and examination of Viking photographs of martian outflow channels is underway.

Beach, G. L.↗
DOE OSTI2023

Synopsis of SURF and SURFplus

Developed by Menikoff and Shaw, the SURF reactive burn model builds on the Ignition and Growth concept by incorporating the lead shock pressure directly into the volumetric hot-spot burn rate. The plus-extension augments the model with a late time surface burn rate due to carbon clustering. Together, SURF and SURFplus allow for robust modeling of both conventional and insensitive high explosives. Practically, the SURF burn models require shock detection and the advection of the lead shock pressure as an additional material field. Calibrated parameters for given equations of state and thermodynamic closure are dependent on initial temperature and density. An implementation in Python is given.

42 ENGINEERING↗
NASA NTRS1999

NASA Microgravity Combustion Science Program

Combustion has been a subject of increasingly vigorous scientific research for over a century, not surprising considering that combustion accounts for approximately 85% of the world's energy production and is a key element of many critical technologies used by contemporary society. Although combustion technology is vital to our standard of living, it also poses great challenges to maintaining a habitable environment. A major goal of combustion research is production of fundamental (foundational) knowledge that can be used in developing accurate simulations of complex combustion processes, replacing current "cut-and-try" approaches and allowing developers to improve the efficiency of combustion devices, to reduce the production of harmful emissions, and to reduce the incidence of accidental uncontrolled combustion. With full understanding of the physics and chemistry involved in a given combustion process, including details of the unit processes and their interactions, physically accurate models which can then be used for parametric exploration of new combustion domains via computer simulation can be developed, with possible resultant definition of radically different approaches to accomplishment of various combustion goals. Effects of gravitational forces on earth impede combustion studies more than they impede most other areas of science. The effects of buoyancy are so ubiquitous that we often do not appreciate the enormous negative impact that they have had on the rational development of combustion science. Microgravity offers potential for major gains in combustion science understanding in that it offers unique capability to establish the flow environment rather than having it dominated by uncontrollable (under normal gravity) buoyancy effects and, through this control, to extend the range of test conditions that can be studied. It cannot be emphasized too strongly that our program is dedicated to taking advantage of microgravity to untangle complications caused by gravity, allowing major strides in our understanding of combustion processes and in subsequent development of improved combustion devices leading to improved quality of life on Earth. Fire and/or explosion events aboard spacecraft could be devastating to international efforts to expand the human presence in space. Testing to date has shown that ignition and flame spread on fuel surfaces (e.g., paper, wire insulation) behave quite differently under partial gravity and microgravity conditions. In addition, fire signatures-i.e., heat release, smoke production, flame visibility, and radiation-are now known to be quite different in reduced gravity environments; this research has provided data to improve the effectiveness of fire prevention practices, smoke and fire detectors, and fire extinguishment systems. The more we can apply our scientific and technological understanding to potential fire behavior in microgravity and partial gravity, the more assurance can be given to those people whose lives depend on the environment aboard spacecraft or eventually on habitats on the Moon or Mars.

King, Merrill K.↗
DOE OSTI2025

Modelling the brittle failure of graphite induced by the controlled impact of runaway electrons in DIII-D

The thermo-mechanical response of an ATJ graphite sample to controlled runaway electron (RE) dissipation, realized in DIII-D, is modelled with a novel work-flow that features the RE orbit code KORC, the Monte Carlo particle transport code Geant4 and the finite element multiphysics software COMSOL. KORC provides the RE striking positions and momenta, Geant4 calculates the volumetric energy deposition and COMSOL simulates the thermoelastic response. Brittle failure is predicted according to the maximum normal stress criterion, which is suitable for ATJ graphite owing to its linear elastic behavior up to fracture and its isotropic mechanical properties. Measurements of the conducted energy, damage topology, explosion timing and blown-off material volume, impose a number of empirical constraints that suffice to distinguish between different RE impact scenarios and to identify RE parameters which provide the best match to the observations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1999

Simulation of Unsteady Hypersonic Combustion Around Projectiles in an Expansion Tube

The temporal evolution of combustion flowfields established by the interaction between wedge-shaped bodies and explosive hydrogen-oxygen-nitrogen mixtures accelerated to hypersonic speeds in an expansion tube is investigated. The analysis is carried out using a fully implicit, time-accurate, computational fluid dynamics code that we developed recently for solving the Navier-Stokes equations for a chemically reacting gas mixture. The numerical results are compared with experimental data from the Stanford University expansion tube for two different gas mixtures at Mach numbers of 4.2 and 5.2. The experimental work showed that flow unstart occurred for the Mach 4.2 cases. These results are reproduced by our numerical simulations and, more significantly, the causes for unstart are explained. For the Mach 5.2 mixtures, the experiments and numerical simulations both produced stable combustion. However, the computations indicate that in one case the experimental data were obtained during the transient phase of the flow; that is, before steady state had been attained.

Yungster, S.↗