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At least 397 records · Page 22

All sources NASA NTRS DOE OSTI

DOE OSTI2022

Deconvolving the roles of E × B shear and pedestal structure in the energy confinement quality of super H-mode experiements

Analysis of “super H-mode” experiments on DIII-D has put forward that high plasma toroidal rotation, not high pedestal, plays the essential role in achieving energy confinement quality H 98y2 >>1. Recently, super H-mode experiments with variable input torque have confirmed that high rotation shear discharges have very high levels of H 98y2 (>1.5), independent of the pedestal height, and that high pedestal discharges with low rotation shear have levels of H 98y2 only slightly above 1 (≤1.2). Although some increase in stored energy with higher pedestal occurs, the energy confinement quality mainly depends on the toroidal rotation shear, which varies according to different levels of injected neutral beam torque per particle. Here, quasi-linear gyrofluid modeling achieves a good match of the experiment when including the E×B shear; without including plasma rotation, the modeling predicts a confinement quality consistent with the empirical observation of H 98y2 ~1.2 at low rotation. Nonlinear gyrokinetic transport modeling shows that the effect of E×B turbulence stabilization is far larger than other mechanisms, such as the so-called hot-ion stabilization (T i /T e ) effect. Consistent with these experimental and modeling results are previous simulations of the ITER Baseline Scenario using a super H-mode pedestal solution, which showed the potential to exceed the Q=10 target if the pedestal density could be increased above the Greenwald limit. A close look at these simulations reveals that the predicted energy confinement quality is below 1 even at the highest pedestal pressure. The improvement in Q at higher pedestal density is due to the improved fusion power generation at the higher core density associated with higher pedestal density, not to an improved energy confinement quality.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS1972

Investigation of GH2-GO2 combustion

Data from prototype GO2-GH2 injection elements were obtained and analyzed. The bulk of the testing was conducted with nonreacting propellants, N2 to simulate the O2 and H2. A limited number of tests were conducted in combusting environment, with the purpose of this testing being to evaluate the effects of combustion on cold flow mixture ratio and mass profiles. The cold flow testing was completed in 223 tests. Analytical model correlations of these data are under way. The hot flow testing was completed in 36 tests. These data have been reduced and are documented in the report.

Calhoon, D. F.↗

NASA NTRS1984

An investigation into the injection molding of PMR-15 polyimide

The chemorheological behavior of the PRM-15 molding compounds were characterized, the range of suitable processing parameters for injection molding in a reciprocating screw injection molding machine was determined, and the effects of the injection molding processing parameters on the mechanical properties of molded PMR-15 parts were studied. The apparatus and procedures for measuring viscosity and for determining the physical response of the material during heating are described. Results show that capillary rheometry can be effectively used with thermosets if the equipment is designed to overcome some of the inherent problems of these materials. A uniform temperature was provided in the barrel by using a circulating hot oil system. Standard capillary rheometry methods can provide the dependence of thermoset apparent viscosity on shear rate, temperature, and time. Process conditions resulting in complete imidization should be carefully defined. Specification of controlled oven temperature is inadequate and can result in incomplete imidization. For completely imidized PMR-15 heat at 15 C/min melt flow without gas evolution occurs in the temperature range of 325 C to 400 C.

Colaluca, M. A.↗

NASA NTRS1986

The dynamic behavior of plasmas observed near geosynchronous orbit

The behavior of plasmas observed by the ATS-6, ATS-5, and SCATHA spacecraft in the vicinity of synchronous orbit in the earth's magnetosphere is investigated. Two predominant features noted are the sudden appearance of injections, and the presence of marked magnetic field-aligned structure. Injections are geosynchronous manifestations of the global acceleration process producing the aurora. Field-aligned fluxes can be as much as two order of magnitude larger than perpendicular fluxes, and ions and electrons often display different field-aligned structure which changes with energy, suggesting field-aligned acceleration processes. Other observed phenomena include particle and field wave activity, and various kinds of plasma heating. Spacecraft charging events illustrate the effects of the hot magnetospheric plasma on material objects.

Mcilwain, C. E.↗

NASA NTRS1986

Experiments on opposed lateral jets injected into swirling crossflow

Experiments have been conducted to obtain the time-mean and turbulent quantities of opposed lateral jets in a low speed, nonreacting flowfield. A jet-to-crossflow velocity ratio of R = v sub J/u sub 0 = 4 was used throughout the experiments, with swirl vane angles of d = 0 (swirler removed), 45 and 70 deg used with the crossflow. Flow visualization techniques used were neutrally-buoyant helium-filled soap bubbles and multispark photography in order to obtain the gross flowfield characteristics. Measurements of time-mean and turbulent quantities were obtained utilizing a six-orientation single hot-wire technique. For the nonswirling case, the jets were found not to penetrate past the test-section centerline, in contrast to the single lateral jet with the same jet-to-crossflow velocity ratio. In the swirling cases, the crossflow remains in a narrow region near the wall of the test section. The opposed jets are swept from their vertical courses into spiral trajectories close to the confining walls. Extensive results are presented in r-x plane plots.

Mcmurry, C. B.↗

NASA NTRS1995

Mass ejections from the sun and their interplanetary counterparts

Since the first observations of solar mass ejection events in the early seventies from OSO 7 and Skylab a few thousand of these remarkable dynamic incidents have been observed by now, covering about two full solar activity cycles. The mass ejecta include mainly hot coronal plasma, plus cold prominence material in variable amounts. The ejecta are often recognised in the form of interplanetary plasma clouds detected in the distant solar wind by appropriately located spacecraft. Clouds which have been energetic enough to drive large scale interplanetary shock waves can be identified most readily, but clouds without associated shocks do also occur. The plasma clouds are characterized by a variety of signatures indicating that they actually originate from injections of different material into the ambient solar wind. Usually only a few of the signatures are found simultaneously. Apparently the bidirectional streaming of halo electrons is a most reliable criterion, indicating a magnetic bottle or plasmoid topology of the clouds. The discussion of the most recent discoveries in this context will show that quite a few crucial problems still remain to be addressed by the upcoming SOHO mission.

Schwenn, R.↗

NASA NTRS1975

Coordinated ATS-5 electron flux and simultaneous auroral observations, appendix B

All Sky Cameras (ASCA) magnetosphere observations were made at the field line conjugate of the ATS-5 Satellite. The magnetosphere region examined was L=5 to L=11. The correlation of the auroras observed by the ASCA's and the magnetospheric trapped fluxes was studied. It is shown that auroral forms are not simply correlated with the synchronous altitude electron fluxes. The presence of hot plasma at the ATS-5 satellite is a necessary but not sufficient condition for the occurrence of local auroras. On quiet days the hot plasma does not penetrate into the magnetosphere far enough to reach the ATS-5 orbit. Under these conditions no auroras are observed at the field line conjugate, but auroras are usually observed on higher latitude field lines. On more disturbed days, auroral arcs are observed at lower latitudes when the plasma sheet penetrates into the ATS-5 orbit. Significant qualitative correlation between the ASCA data and the trapped fluxes was observed when a local plasma injection event occurred near ATS-5. Magnetograms are shown.

Mende, S. B.↗

NASA NTRS1985

Film cooling on a convex wall: Heat transfer and hydrodynamic measurements for full and partial coverage

Turbine-blade cooling is an important issue for high-efficiency turbine engines, and discrete-hole injection is widely used as a cooling method. In the present study, detailed measurements were made of the heat transfer and hydrodynamics of a film-cooled flow on a convex wall, both for full and partial coverage. Two important parameters were altered: the blowing ratio, m, and the number of rows of injection holes. Three values of m were tested: m = 0.2, 0.4, and 0.6. In the blown region, m = 0.4 results in the lowest Stanton numbers of the three blowing ratios tested. This indicates that the value of m = 0.4 is near optimum on the convex wall from the point of view of cooling effect by injection. In the recovery region, Stanton numbers gradually approach the no injection values. Although the heat-transfer behavior during recovery from injection looks relatively complicated, the behavior of Stanton number can be explained in terms of two mechanisms: recovery from the thermal effect of injection and recovery from the turbulence augmentation. This interpretation of the data is supported by the hydrodynamic and temperture-profile measurements. For partial blowing cases, the data follow the full-coverage values inside the blown region. In the unblown region, both in the curved and in the flat plate, the effect of the number of blown rows is clearly seen. Hydrodynamic boundary-layer profiles were measured with the aid of a triple hot-water probe. Three mean-velocity components and six turbulence quantities were simultaneously measured, and inside the blown region strong three-dimensionality was observed.

Furuhama, K.↗

NASA NTRS2014

Development of Modeling Approaches for Nuclear Thermal Propulsion Test Facilities

High efficiency of rocket propul-sion systems is essential for humanity to venture be-yond the moon. Nuclear Thermal Propulsion (NTP) is a promising alternative to conventional chemical rock-ets with relatively high thrust and twice the efficiency of the Space Shuttle Main Engine. NASA is in the pro-cess of developing a new NTP engine, and is evaluat-ing ground test facility concepts that allow for the thor-ough testing of NTP devices. NTP engine exhaust, hot gaseous hydrogen, is nominally expected to be free of radioactive byproducts from the nuclear reactor; how-ever, it has the potential to be contaminated due to off-nominal engine reactor performance. Several options are being investigated to mitigate this hazard potential with one option in particular that completely contains the engine exhaust during engine test operations. The exhaust products are subsequently disposed of between engine tests. For this concept (see Figure 1), oxygen is injected into the high-temperature hydrogen exhaust that reacts to produce steam, excess oxygen and any trace amounts of radioactive noble gases released by off-nominal NTP engine reactor performance. Water is injected to condense the potentially contaminated steam into water. This water and the gaseous oxygen (GO2) are subsequently passed to a containment area where the water and GO2 are separated into separate containment tanks.

Jones, Daniel R.↗

NASA NTRS1994

Particle acceleration in the dynamic magnetotail: Orbits in self-consistent three-dimensional MHD fields

The acceleration of protons in a dynamically evolving magnetotail is investigated by tracing particles in the fields obtained from a three-dimensional resistive magnetohydrodynamic (MHD) simulation. The MHD simulation, representing plasmoid formation and ejection through a near-Earth reconnection process, leads to cross-tail electric fields of up to approximately 4 mV/m with integrated voltages across the tail of up to approximately 200 kV. Energization of particles takes place over a wide range along the tail, due to the large spatial extent of the increased electric field together with the finite cross-tail extent of the electric field region. Such accelerated particles appear earthward of the neutral line over a significant portion of the closed field line region inside of the separatrix, not just in the vicinity of the separatrix. Two different acceleration processes are identified: a 'quasi-potential' acceleration, due to particle motion in the direction of the cross-tail electric field, and a 'quasi-betatron' effect, which consists of multiple energy gains from repeated crossings of the acceleration region, mostly on Speiser-type orbits, in the spatially varying induced electric field. The major source region for accelerated particles in the hundreds of keV range is the central plasma sheet at the dawn flank outside the reconnection site. Since this source plasma is already hot and dense, its moderate energization by a factor of approximately 2 may be sufficient to explain the observed increases in the energetic particle fluxes. Particles from the tail are the source of beams at the plasma sheet/lobe boundary. The temporal increase in the energetic particle fluxes, estimated from the increase in energy gain, occurs on a fast timescale of a few minutes, coincident with a strong increase in B(sub z), despite the fact that the inner boundary ('injection boundary') of the distribution of energized particles is fairly smooth.

Birn, Joachim↗

DOE OSTI2025

Monte Carlo Simulations of Polarized Radiative Transfer in Neutron Star Atmospheres

Soft X-ray emission from neutron stars affords powerful diagnostic tools for uncovering their surface and interior properties, as well as their geometric configurations. In the atmospheres of neutron stars, the presence of magnetic fields alters the photon-electron scattering cross sections, resulting in nontrivial angular dependence of intensity and polarization of the emergent signals. This paper presents recent developments of our Monte Carlo simulation, MAGTHOMSCATT, which tracks the complex electric field vector for each photon during its transport. Our analysis encompasses the anisotropy and polarization characteristics of X-ray emission for field strengths ranging from nonmagnetic to extremely magnetized regimes that are germane to magnetars. In the very low field domain, we reproduced the numerical solution to the radiative transfer equation for nonmagnetic Thomson scattering, and provided analytical fits for the angular dependence of the intensity and the polarization degree. These fits can be useful for studies of millisecond pulsars and magnetic white dwarfs. By implementing a refined injection protocol, we show that, in the magnetar regime, the simulated intensity and polarization pulse profiles of emission from extended surface regions becomes invariant with respect to the ratio of photon (ω) and electron cyclotron (ω B ) frequencies once ω/ω B ≲ 0.01. This circumvents the need for simulations pertinent to really high magnetic field strengths, which are inherently slower. Our approach will be employed elsewhere to model observational data to constrain neutron star geometric parameters and properties of emitting hot spots on their surfaces.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1988

Global Geospace Science Programme

The Global Geospace Science (GGS) Program, an element of the international Solar Terrestrial Physics Program dedicated to the study of the global plasma dynamics of the solar-terrestrial environment, is discussed. Past research on the injection of solar wind ions into the magnetosphere and on the detection of ions in the terrestrial ring current of both solar wind and ionospheric origins is reviewed, showing its relevance for the GGS program. Research on the interplanetary magnetic field, the auroral electrojet, the outer magnetosphere, the geomagnetic tail, the ionospheric electric field and the related electron precipitation is also addressed. The results demonstrate that the solar wind and the ionsophere both contribute to the magnetospheric particle population. Unanswered questions regarding hot plasma sources, transport processes, energy storage in the magnetic field, and energization of plasmas are discussed. The relevant mission strategy, instrumentation, theory and modeling, and data collection are addressed.

Parks, George↗

NASA NTRS2007

Experimental Measurements of Two-dimensional Planar Propagating Edge Flames

The study of edge flames has received increased attention in recent years. This work reports the results of a recent study into two-dimensional, planar, propagating edge flames that are remote from solid surfaces (called here, free-layer flames, as opposed to layered flames along floors or ceilings). They represent an ideal case of a flame propagating down a flammable plume, or through a flammable layer in microgravity. The results were generated using a new apparatus in which a thin stream of gaseous fuel is injected into a low-speed laminar wind tunnel thereby forming a flammable layer along the centerline. An airfoil-shaped fuel dispenser downstream of the duct inlet issues ethane from a slot in the trailing edge. The air and ethane mix due to mass diffusion while flowing up towards the duct exit, forming a flammable layer with a steep lateral fuel concentration gradient and smaller axial fuel concentration gradient. We characterized the flow and fuel concentration fields in the duct using hot wire anemometer scans, flow visualization using smoke traces, and non-reacting, numerical modeling using COSMOSFloWorks. In the experiment, a hot wire near the exit ignites the ethane air layer, with the flame propagating downwards towards the fuel source. Reported here are tests with the air inlet velocity of 25 cm/s and ethane flows of 967-1299 sccm, which gave conditions ranging from lean to rich along the centerline. In these conditions the flame spreads at a constant rate faster than the laminar burning rate for a premixed ethane air mixture. The flame spread rate increases with increasing transverse fuel gradient (obtained by increasing the fuel flow rate), but appears to reach a maximum. The flow field shows little effect due to the flame approach near the igniter, but shows significant effect, including flow reversal, well ahead of the flame as it approaches the airfoil fuel source.

Villa-Gonzalez, Marcos↗

NASA NTRS2012

Aero-Thermal Calibration of the NASA Glenn Icing Research Tunnel (2012 Test)

A major modification of the refrigeration plant and heat exchanger at the NASA Glenn Icing Research Tunnel (IRT) occurred in autumn of 2011. It is standard practice at NASA Glenn to perform a full aero-thermal calibration of the test section of a wind tunnel facility upon completion of major modifications. This paper will discuss the tools and techniques used to complete an aero-thermal calibration of the IRT and the results that were acquired. The goal of this test entry was to complete a flow quality survey and aero-thermal calibration measurements in the test section of the IRT. Test hardware that was used includes the 2D Resistive Temperature Detector (RTD) array, 9-ft pressure survey rake, hot wire survey rake, and the quick check survey rake. This test hardware provides a map of the velocity, Mach number, total and static pressure, total temperature, flow angle and turbulence intensity. The data acquired were then reduced to examine pressure, temperature, velocity, flow angle, and turbulence intensity. Reduced data has been evaluated to assess how the facility meets flow quality goals. No icing conditions were tested as part of the aero-thermal calibration. However, the effects of the spray bar air injections on the flow quality and aero-thermal calibration measurements were examined as part of this calibration.

Pastor-Barsi, Christine↗

NASA NTRS2012

Aero-Thermal Calibration of the NASA Glenn Icing Research Tunnel (2012 Test)

Pastor-Barsi, Christine M.↗

NASA NTRS1972

Analysis and comparison of wall cooling schemes for advanced gas turbine applications

The relative performance of (1) counterflow film cooling, (2) parallel-flow film cooling, (3) convection cooling, (4) adiabatic film cooling, (5) transpiration cooling, and (6) full-coverage film cooling was investigated for heat loading conditions expected in future gas turbine engines. Assumed in the analysis were hot-gas conditions of 2200 K (3500 F) recovery temperature, 5 to 40 atmospheres total pressure, and 0.6 gas Mach number and a cooling air supply temperature of 811 K (1000 F). The first three cooling methods involve film cooling from slots. Counterflow and parallel flow describe the direction of convection cooling air along the inside surface of the wall relative to the main gas flow direction. The importance of utilizing the heat sink available in the coolant for convection cooling prior to film injection is illustrated.

Colladay, R. S.↗

NASA NTRS1975

Ionosphere-magnetosphere coupling. I - Thermal plasma

The complex interaction of the cold plasma of the plasmasphere and ionosphere with the hot plasma of the ring current and the plasma sheet is studied. It is seen that a coupling, probably through wave particle interactions, exists which seems to have a strong influence on the temperature of the plasma of the outer plasmasphere and on the detailed dynamics of the bulge region, especially the formation of detached plasma regions or plasma tails. Also, there is evidence that the outer plasmasphere may display very high temperatures, and that detached plasma regions are closely associated with ring current injections.

Chappell, C. R.↗

DOE OSTI2024

Thermal and Well Flow Performance of Closed-Loop Geothermal in the Wattenberg Area: Preprint

Closed-loop geothermal systems provide an alternative to resource-constrained hydrothermal systems and stimulation-intensive enhanced geothermal systems. In this work, we apply the slender-body theory (SBT) model, to simulate the well flow and heat transfer performance of U-loop well designs drilled in the Wattenberg area of the Denver-Julesburg Basin. Three U-loop well patterns are investigated including a single, double, and multi-lateral design. The subsurface within area is characterized by deep, hot (> 200degreesC) igneous/metamorphic basement rock underlying multiple sedimentary formations. The lateral section(s) of the U-loop lies within a target depth of 6 km where temperatures are estimated to approach 300degreesC. As a base case, conduction-only heat transfer is investigated through simulations with the SBT model within U-loops with open-hole laterals that exchange heat directly with the hot dry rock using water as a working fluid. The utilization of supercritical CO2 as a heat transfer fluid is also considered. For each scenario, the system performance in terms of annual heat production and temperature profile over a 20-year project lifetime are assessed. Also, the levelized costs of heat and electricity (LCOH and LCOE) are determined using a top-down technoeconomic analysis model. The results show that the performance and cost optimized U-loop design is one having an injection-production well spacing of 1,000 meters with ten 50-meter-spaced laterals that traverse a subsurface system with a temperature gradient of 60degreesC/km. By injecting 20 degreesC-water at a rate of 60 kg/s through this loop, an average heat production of 19 MWth can be achieved, resulting in an LCOE and LCOH of $136/MWh and $1.53/GJ, respectively, over a 20-year project life.

closed-loop geothermal↗