Search NASA⌕ Search

SEARCH · Search NASA

Results for “pressure scale”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Turbulent broadening of electron heat-flux width in electromagnetic gyrokinetic simulations of a helical scrape-off layer model

Here, we demonstrate that cross field transport in the scrape-off layer (SOL) can be moderately increased by electromagnetic effects in high-beta regimes, resulting in broadening of the electron heat-flux width on the endplates. This conclusion is taken from full- f electromagnetic gyrokinetic simulations of a helical SOL model that roughly approximates the SOL of the National Spherical Torus Experiment. The simulations have been performed with the Gkeyll code, which recently became the first code to demonstrate the capability to simulate electromagnetic gyrokinetic turbulence on open magnetic field lines with sheath boundary conditions. We scan the source rate and thus β, so that the normalized pressure gradient (the MHD ballooning parameter $α ∝ ∂β/∂r ∝ β/Lρ$) is scanned over an experimentally relevant range, α = 0.3 - 1.5. While there is little change in the pressure gradient scale length L p near the midplane as beta is increased, a 10% increase in cross field transport near the midplane results in an increase in the electron heat-flux width λ q and a 25% reduction of the peak electron heat flux to the endplates.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Modeling atomically mixed graded density impactors

Graded density impactors (GDIs) are multi-material composite impactors used in gas gun experiments to tailor the drive conditions imparted to a sample test material. Previous graded density impactors generally rely on thin, but discrete, layers of different materials. The thinner and the greater number of layers will result in smoother compression. Taken to the limit of very thin layers would be pure material 1 at one surface, such as the front surface of an impactor, smoothly transitioning at the atomic scale to pure material 2 on the back surface. Such an impactor can initially shock, then smoothly compresses a material during a dynamic experiment. This type of experiment can serve to explore a larger region of thermodynamic space than a single or even multi-shock experiments. An overview of how graded density impactors are made is reviewed and sample results are given. Additionally, a strategy for modeling these kinds of impactors is presented. The length scales of constituent mixing are given from the experimental build through electrochemical-deposition. Equation of state models for pure constituents and their subsequent mixtures are presented. It is demonstrated that the time scales for pressure and temperature equilibration, for atomically mixed GDIs, are short enough to be a justifiable closure for the resulting multiphase flow. Furthermore, we present simulation results of dynamic shock followed by a ramp compression, utilizing a silver/gold graded density impactor, onto a tantalum sample.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Mitigation of backgrounds from cosmogenic 137 Xe in xenon gas experiments using 3 He neutron capture

136 Xe is used as the target medium for many experiments searching for 0νββ. Despite underground operation, cosmic muons that reach the laboratory can produce spallation neutrons causing activation of detector materials. A potential background that is difficult to veto using muon tagging comes in the form of 137 Xe created by the capture of neutrons on 136 Xe. This isotope decays via beta decay with a half-life of 3.8 minutes and a Q β of ~4.16 MeV. This work proposes and explores the concept of adding a small percentage of 3 He to xenon as a means to capture thermal neutrons and reduce the number of activations in the detector volume. When using this technique we find the contamination from 137 Xe activation can be reduced to negligible levels in tonne and multi-tonne scale high pressure gas xenon neutrinoless double beta decay experiments running at any depth in an underground laboratory.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Experimental study on the role of the target electron temperature as a key parameter linking recycling to plasma performance in JET-ILW*

Changes in global and edge plasma parameters (H98(y,2), dimensionless collisionality ν*, core density peaking, separatrix density ne,sep) with variations in the D2 fueling rate and divertor configuration are unified into a single trend when mapped to $\langle$Te,ot$\rangle$, the spatially averaged spectroscopically derived outer target electron temperature. Dedicated JET with the ITER-like wall (JET-ILW) experiments in combination with an extended JET-ILW database of unseeded low-triangularity H-mode plasmas spanning a wide range of D2 fueling rates, Ip, Bt and heating power have demonstrated the importance of $\langle$Te,ot$\rangle$ as a key physics parameter linking the recycling particle source and detachment with plasma performance. The remarkably robust H98(y,2) trend with $\langle$Te,ot$\rangle$ is connected to a strong inverse correlation between $\langle$Te,ot$\rangle$, ne,sep and ν*, thus directly linking changes in the divertor recycling moderated by $\langle$Te,ot$\rangle$ with the previously established relationship between ν*, core density peaking and core pressure resulting in a degradation in core plasma performance with decreasing $\langle$Te,ot$\rangle$ (increasing ν*). Additionally, a strong inverse correlation between the separatrix to pedestal density ratio, ne,sep/ne,ped, and $\langle$Te,ot$\rangle$ is also established, with the rise in ne,sep/ne,ped saturating at $\langle$Te,ot$\rangle$ > 10 eV. A strong reduction in H98(y,2) is observed as $\langle$Te,ot$\rangle$ is driven from 30 to 10 eV via additional D2 gas fueling, while the divertor remains attached. Consequently, the pronounced performance degradation in attached divertor conditions has implications for impurity seeding radiative divertor scenarios, in which H98(y,2) is already low (~0.7) before impurities are injected into the plasma since moderate gas fueling rates are required to promote high divertor neutral pressure. A favorable pedestal pressure, pe,ped, dependence on Ip has also been observed, with an overall increase in pe,ped at Ip = 3.4 MA as $\langle$Te,ot$\rangle$ is driven down from attached to high-recycling divertor conditions. In contrast, pe,ped is reduced with decreasing $\langle$Te,ot$\rangle$ in the lower Ip branches. Further work is needed to (i) clarify the potential role of edge opacity on the observed favorable pedestal pressure Ip scaling; as well as to (ii) project the global and edge plasma performance trends with $\langle$Te,ot$\rangle$ to reactor-scale devices to improve predictive capability of the coupling between recycling and confined plasma fueling in what are foreseen to be more opaque edge plasma conditions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Determination of confinement regime boundaries via separatrix parameters on Alcator C-Mod based on a model for interchange-drift-Alfvén turbulence

The separatrix operational space (SepOS) model (Eich and Manz 2021 Nucl. Fusion 61 086017) is shown to predict the L–H transition, the L-mode density limit, and the ideal magnetohydrodynamic ballooning limit in terms of separatrix parameters for a wide range of Alcator C-Mod plasmas. The model is tested using Thomson scattering measurements across a wide range of operating conditions on C-Mod, spanning $\overline{n}_{\mathrm{e}}$ = 0.3–5.5 $\times 10^{20}\,$m −3 , $B_{\mathrm{t}} = 2.5$–8.0 T, and $B_{\mathrm{p}}$= 0.1–1.2 T. An empirical regression for the electron pressure gradient scale length, $\lambda_{{p}_{\mathrm{e}}}$, against a turbulence control parameter, $\alpha_{\mathrm{t}}$, and the poloidal fluid gyroradius, $\rho_{\mathrm{s,p}}$, is constructed for H-modes and found to require positive exponents for both regression parameters, indicating turbulence widening of near-scrape-off layer widths at high $\alpha_{\mathrm{t}}$ and an inverse scaling with $B_{\mathrm{p}}$, consistent with results on ASDEX Upgrade. The SepOS model is also tested in the unfavorable drift direction and found to apply well to all three boundaries, including the L–H transition as long as a correction to the Reynolds energy transfer term, $\alpha_\mathrm{RS} \lt 1$ is applied. I-modes typically exist in the unfavorable drift direction for values of $\alpha_{\mathrm{t}} \lesssim 0.3$. Finally, an experiment studying the transition between the Type-I ELMy and EDA H-mode is analyzed using the same framework. It is found that a recently identified boundary $\alpha_{\mathrm{t}} = 0.55$ at excludes most EDA H-modes but that the balance of wavenumbers responsible for the L-mode density limit, namely $k_\mathrm{EM} = k_\mathrm{RBM}$, may better describe the transition on C-Mod. The ensemble of boundaries validated and explored is then applied to project regime access and limit avoidance for the SPARC primary reference discharge parameters.

ELM suppression↗
DOE OSTI2025

The impact of varying inhomogeneous reionization histories on metrics of Ly α opacity

The epoch of hydrogen reionization is complete by z = 5⁠, but its progression at higher redshifts is uncertain. Measurements of Ly α forest opacity show large scatter at z < 6⁠, suggestive of spatial fluctuations in neutral fraction, temperature, or ionizing background, either individually or in combination. However, there are degeneracies in the impact of such fluctuations, necessitating careful modelling. We develop a framework for modelling the reionization history and associated temperature fluctuations, with the intention of incorporating ionizing background fluctuations at a later time. We generate several reionization histories using seminumerical code AMBER, and implement them in the Nyx cosmological hydrodynamics code to examine the impact on the evolution of gas within the simulation and the associated metrics of the Ly α forest opacity. We find that the pressure smoothing scale within the intergalactic medium is strongly correlated with the adiabatic index of the temperature–density relation. We find that while models with 20 000 K photoheating at reionization are better able to reproduce the shape of the observed z = 5 1D flux power spectrum than colder ones, they fail to match the highest wavenumbers. The simulated autocorrelation function and optical depth distributions are systematically low and narrow, respectively, compared to the observed values, but are in better agreement when the reionization history is longer in duration, more symmetric in its distribution of reionization redshifts, or if there are remaining neutral regions at z < 6.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

The Observed Inefficiency of Explosions to Produce Large Aftershocks: Båth’s Law for Explosions is 2.5

Underground explosions are observed to produce fewer and smaller aftershocks than similar size earthquakes. The seismic magnitude difference $Δm_x$ between an explosion and its largest aftershock is an expression of Båth’s law for explosions. Based on an analysis of a compilation of aftershock studies from Soviet testing at the Semipalatinsk test site in Kazakhstan and observations from American testing at the Nevada National Security Site (NNSS), here we find that the average magnitude difference for explosions $\overline{Δm_x}$ is about 2.5. Based on the NNSS data, two standard deviations of $Δm_x$ is about 1.5. In all the cases studied, from ton to megaton yield, from shallow to overburied depth, and chemical or nuclear source, no explosion aftershock has been larger than the explosion that preceded it. In fact, the two events at the NNSS with the largest aftershock magnitudes relative to the explosion are associated with the collapse of the cavity created by the explosion. This is similar to observations from North Korean testing at the Punggye-ri Test Site, where the largest seismic event following the test is attributed to the collapse after the 2017 explosion and is from 0.8 to 2 magnitude units less than the mainshock.

58 GEOSCIENCES↗
DOE OSTI2020

Discriminating Accretion States via Rotational Symmetry in Simulated Polarimetric Images of M87

In 2017 April, the Event Horizon Telescope observed the shadow of the supermassive black hole at the core of the elliptical galaxy Messier 87. While the original image was constructed from measurements of the total intensity, full polarimetric data were also collected, and linear polarimetric images are expected in the near future. We propose a modal image decomposition of the linear polarization field into basis functions with varying azimuthal dependence of the electric vector position angle. We apply this decomposition to images of ray traced general relativistic magnetohydrodynamics simulations of the Messier 87 accretion disk. Furthermore, for simulated images that are physically consistent with previous observations, the magnitude of the coefficient associated with rotational symmetry, β2, is a useful discriminator between accretion states. We find that at 20 μas resolution, $| {\beta }_{2}| $ is greater than 0.2 only for models of disks with horizon-scale magnetic pressures large enough to disrupt steady accretion. We also find that images with a more radially directed electric vector position angle correspond to models with higher black hole spin. Our analysis demonstrates the utility of the proposed decomposition as a diagnostic framework to improve constraints on theoretical models.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1973

Investigation of the effect of inlet turbulence length scale on fan discrete tone noise

Results of an experimental investigation at the Ames 40- by 80-Foot Wind Tunnel of fan rotor alone discrete tone noise is presented. The investigation examines rotor interaction with fan inlet turbulence. The importance of turbulence length scale is shown by comparing the fan radiated acoustic spectrum with and without modified turbulence length scales. A small-scale low pressure ratio fan was used for the experiment.

Hodder, B. K.↗
NASA NTRS1974

Comparison of transition and freestream disturbance measurements obtained in two wind tunnel facilities

Boundary-layer transition measurements have been made on two 5-deg half-angle cones at Mach 7 in the Ames 3.5-foot and the Langley variable density wind tunnels. Although there were differences between the measured freestream disturbance scales and pressure fluctuation levels, the choice of consistent locations within the transition region, using either thin-film fluctuation or surface heat-transfer data results in excellent agreement between the transition Reynolds numbers in both facilities. However, there is an apparent connection between changes in freestream pressure fluctuation levels and movement of boundary-layer transition location in the two facilities.

Owen, F. K.↗
NASA NTRS1976

Methods for data reduction and loads analysis of Space Shuttle Solid Rocket Booster model water impact tests

The methodology used to predict full scale space shuttle solid rocket booster (SRB) water impact loads from scale model test data is described. Tests conducted included 12.5 inch and 120 inch diameter models of the SRB. Geometry and mass characteristics of the models were varied in each test series to reflect the current SRB baseline configuration. Nose first and tail first water entry modes were investigated with full-scale initial impact vertical velocities of 40 to 120 ft/sec, horizontal velocities of 0 to 60 ft/sec., and off-vertical angles of 0 to plus or minus 30 degrees. The test program included a series of tests with scaled atmospheric pressure.

Source record↗
NASA NTRS1977

Space shuttle pogo studies

Topics covered include: (1) pogo suppression for main propulsion subsystem operation; (2) application of quarter-scale low pressure oxidizer turbopump transfer functions; (3) pogo stability during orbital maneuvering subsystem operation; and (4) errors in frequency response measurements.

Coppolino, R. N.↗
NASA NTRS1972

Wind-tunnel measurements of aerodynamic load distribution on an NASA supercritical-wing research airplane configuration

Wind tunnel tests have been conducted on a research airplane model with an NASA supercritical wing to define the general character of the flow over the wing and to aid in structural design of the full scale airplane. Pressure measurements were made at Mach numbers from 0.25 to 1.30 for sideslip angles from -2.50 deg to 2.50 deg over a moderate range of angles of attack and dynamic pressures. Except for representative figures, the results are presented in tabular form without detailed analysis.

Harris, C. D.↗
NASA NTRS1978

Microbial Check Valve for Shuttle

The Microbial Check Valve (MCV) is a device developed for the Space Shuttle that prevents the transfer of viable microorganisms within water systems. The device is essentially a bed of resin material, impregnated with iodine, that kills microorganisms on contact. It prevents the cross-contamination of microorganisms from a nonpotable system into the potable water system when these systems are interconnected. In this regard, the function of the device is similar to that of the 'air gap' found in conventional one-gravity systems. Basic design data are presented including pressure drop, scaling factors, sizing criteria, and the results of challenging the device with suspensions of seven microorganisms including aerobes, anaerobes and spore formers.

Colombo, G. V.↗