Search NASA⌕ Search

SEARCH · Search NASA

Results for “CTR”

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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Single and double point modeling of homogeneous turbulence

Investigations carried out for revisiting homogeneous turbulent flows in the presence of mean shear, rotation, or external compression are summarized. The simplest and most concise RDT (Rapid Distortion Theory) formulation, which includes a comprehensive linear stability analysis, is used for this purpose. Such a linear approach could be extended by a generalized EDQNM (Eddy Damped Quasi-Normal Markovian) to two point closure in order to model non-linear interactions, especially when pure Coriolis effects are present. The results are discussed in connection with databases obtained by DNS (Direct Numerical Simulations), including previous Center for Turbulence Research (CTR) results and new calculations in progress. The main goal is to contribute to and significantly improve on the rational one-point closure models in progress at the CTR and at Ecole Centrale de Lyon (ECL).

Cambon, C.↗
NASA NTRS1994

Studying Turbulence Using Numerical Simulation Databases. 5: Proceedings of the 1994 Summer Program

Direct numerical simulation databases were used to study turbulence physics and modeling issues at the fifth Summer Program of the Center for Turbulence Research. The largest group, comprising more than half of the participants, was the Turbulent Reacting Flows and Combustion group. The remaining participants were in three groups: Fundamentals, Modeling & LES, and Rotating Turbulence. For the first time in the CTR Summer Programs, participants included engineers from the U.S. aerospace industry. They were exposed to a variety of problems involving turbulence, and were able to incorporate the models developed at CTR in their company codes. They were exposed to new ideas on turbulence prediction, methods which already appear to have had an impact on their capabilities at their laboratories. Such interactions among the practitioners in the government, academia, and industry are the most meaningful way of transferring technology.

Source record↗
NASA NTRS1994

The coupling between flame surface dynamics and species mass conservation in premixed turbulent combustion

Current flamelot models based on a description of the flame surface dynamics require the closure of two inter-related equations: a transport equation for the mean reaction progress variable, (tilde)c, and a transport equation for the flame surface density, Sigma. The coupling between these two equations is investigated using direct numerical simulations (DNS) with emphasis on the correlation between the turbulent fluxes of (tilde)c, bar(pu''c''), and Sigma, (u'')(sub S)Sigma. Two different DNS databases are used in the present work: a database developed at CTR by A. Trouve and a database developed by C. J. Rutland using a different code. Both databases correspond to statistically one-dimensional premixed flames in isotropic turbulent flow. The run parameters, however, are significantly different, and the two databases correspond to different combustion regimes. It is found that in all simulated flames, the correlation between bar(pu''c'') and (u'')(sub S)Sigma is always strong. The sign, however, of the turbulent flux of (tilde)c or Sigma with respect to the mean gradients, delta(tilde)c/delta(x) or delta(Sigma)/delta(x), is case-dependent. The CTR database is found to exhibit gradient turbulent transport of (tilde)c and Sigma, whereas the Rutland DNS features counter-gradient diffusion. The two databases are analyzed and compared using various tools (a local analysis of the flow field near the flame, a classical analysis of the conservation equation for (tilde)(u''c''), and a thin flame theoretical analysis). A mechanism is then proposed to explain the discrepancies between the two databases and a preliminary simple criterion is derived to predict the occurrence of gradient/counter-gradient turbulent diffusion.

Trouve, A.↗
NASA NTRS1996

The smart highway project: Smart highways, smart vehicles, smart engineering

The Smart Highway project is a six mile, limited access roadway being built between Interstate 81 and Blacksburg, Virginia. The initial construction segment will be two miles long and is designed to serve as a test bed and test track for Intelligent Transportation Systems (ITS) research. The Center for Transportation Research (CTR) at Virginia Tech is developing three evaluation tools for its ITS research including DYNAVIMTS (a software framework), and the FLASH Lab (a 1/15th scale model highway and vehicle system). The Smart Highway rounds out the Center's evaluation methodology by allowing full scale operational tests, evaluations, and research under both experimental and conventional traffic conditions. Currently under development is a concept for a fully automated highway using a 'Cooperative Infrastructure Managed System' which involves ultra wide band communication beacons installed in the infrastructure with appropriate sensors, receivers and processors on board the vehicles. The project is part of the research program funded by the National Automated Highway System Consortium. The CTR hopes to develop the automated concept to prototype status by 1997. Other smart transportation and smart engineering concepts are proposed. This presentation will address the goals and objectives of the Smart Highway project, overview its status and importance to the region, and identify some of the transportation technology now under development and planned in the future.

Pethtel, Ray D.↗
NASA NTRS2005

Advanced Combustion Modeling for Complex Turbulent Flows

The next generation of aircraft engines will need to pass stricter efficiency and emission tests. NASA's Ultra-Efficient Engine Technology (UEET) program has set an ambitious goal of 70% reduction of NO(x) emissions and a 15% increase in fuel efficiency of aircraft engines. We will demonstrate the state-of-the-art combustion tools developed a t Stanford's Center for Turbulence Research (CTR) as part of this program. In the last decade, CTR has spear-headed a multi-physics-based combustion modeling program. Key technologies have been transferred to the aerospace industry and are currently being used for engine simulations. In this demo, we will showcase the next-generation combustion modeling tools that integrate a very high level of detailed physics into advanced flow simulation codes. Combustor flows involve multi-phase physics with liquid fuel jet breakup, evaporation, and eventual combustion. Individual components of the simulation are verified against complex test cases and show excellent agreement with experimental data.

Ham, Frank Stanford↗
NASA NTRS2009

Short Field Take-Off and Landing Performance as an Enabling Technology for a Greener, More Efficient Airspace System

The Cruise Efficient Short Take-Off and Landing (CESTOL) aircraft and Civil Tiltrotor (CTR) are two examples of powered-lift aircraft concepts that are of interest to NASA. These concepts will be able to utilize the shorter unused or underutilized runways and corresponding airspace at the crowded hub airports and many unused airfields and airspace that currently exist in other expanding urban areas providing additional capacity to the airspace system and reductions in congestion and delays seen in the current system. By treating the use of CESTOL and CTR as critical components that supplement other green aircraft to be used in the overall airspace system, the efficiency and improvements gained by the entire system will offset the potential increased fuel usage and emissions that may be a result of providing short field capability to the powered-lift aircraft. My presentation will address how NASA and the aerospace industry may identify, analysis, and finally implement these powered-lift aircraft into the airspace system and improve the capacity and reduce delay, while obtaining an overall reduction in noise, fuel usage, and emissions.

Hange, Craig E.↗
NASA NTRS2016

Measurements of Proton Displacement Damage in Several Commercial Optocouplers

Proton Displacement Damage (DD) measurements on Isolink OLS049, Micropac 66296-101, 66224-103JANTX, and 66179-003 are reported. The 66179-003 has the worst degradation, 13% of the initial CTR remains when it is used with I(sub F) = 10 mA at 1 x 10(exp 12) 1-MeV n/sq.cm fluence in Silicon. The remaining CTR percentage for OLS049, 66296-101, and 66224-103JANTX are 21%, 32%, and 79% at 2 x 10(exp 12) 1-MeV n/sq.cm fluence in Silicon, respectively.

Irom, Farokh↗
DOE OSTI2024

Impurity-enhanced core valence luminescence via Zn-doping in cesium magnesium chlorides

Scintillators with faster timing capabilities are currently in high demand for use in radiation detection systems in the fields of nuclear and medical physics. The limited number of suitable materials that meet the performance criteria of next generation detection systems presents an opportunity for discovery of new fast scintillator materials. In this work, the effects of doping several ultrafast core-valence luminescent (CVL) scintillators with divalent Zn is explored. Three compounds are investigated – CsMgCl 3 , Cs 2 MgCl 4 , and Cs 3 MgCl 5 – and single crystals of each doped with 5 mol% Zn are grown via the Bridgman method. Additionally, mixing across the full range of concentrations (from 0 % to 100 % Zn) is explored in the Cs 2 Mg 1-x Zn x Cl 4 and Cs 3 Mg 1-x Zn x Cl 5 systems. For low concentrations of Zn, light yields of all three compounds are enhanced (by up to ~60 %) compared to the pure crystals, achieving what we believe to be the brightest known CVL, CsMgCl 3 :Zn 5 % (3400 ± 170 ph/MeV light yield). More importantly, Zn doping does not affect the ultrafast timing properties, with each composition maintaining a single-component decay time around 1–3 ns. A sub-100 ps coincidence time resolution (CTR) is also achieved with CsMgCl 3 :Zn 5 %. The results of this work reveal a new avenue towards obtaining brighter CVL materials, which could open up possibilities for more advanced ultrafast scintillators to be discovered moving forward.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Structure of the Bastnäsite (001) Surface by Crystal Truncation Rod X-ray Diffraction and Ab Initio Molecular Dynamics: Implications for Separations of a Rare Earth Ore Mineral

Bastnäsite ((Ce,La)FCO 3 ) is the primary mineral source of light rare earth elements, but its surface structure is not well understood. This presents a major challenge in improving beneficiation strategies. In this work, a synergistic combination of X-ray scattering and ab initio molecular dynamics (AIMD) was used to gain atomistic insight into the interfacial structure of bastnäsite. Surface X-ray scattering was used to measure crystal truncation rods (CTRs) of the bastnäsite (001) surface, a significant crystal face with a previously unknown termination. The best-fit atomic-scale model of the CTR data features a carbonate layer at the surface, which is stabilized by the relaxation of carbonate groups from their bulk structural positions. AIMD simulations predict similar surface relaxations, which are shown to be influenced by the protonation of oxygen atoms at the surface. Evidence of ordered water at the interface is also observed in the best-fit model and AIMD simulations. Further, the presence of a carbonate layer at this dominant crystal surface is significant for improving separation technologies because most commonly used ligands utilize anionic functional groups to chelate metal cations at particle surfaces. Without modification, anionic ligands are expected to have poor affinity for the carbonate-terminated (001) surface.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Enhancing the Cherenkov over scintillation ratio using dichroic filters in BGO and TlCl for TOF-PET

Abstract The Cherenkov emission in inorganic crystal scintillators has been shown to dramatically improve time resolution for time-of-flight positron emission tomography (TOF-PET) for in slow scintillators with a high refractive index such as bismuth germanium oxide (BGO). This is due to the faster nature of the Cherenkov emission (tens of picoseconds) with respect to scintillation (nanosecond). However, the presence of slower scintillation light and the inability of existing detectors to distinguish between Cherenkov and scintillation make it difficult for BGO to achieve a good CTR for all the detected coincidence events. In this paper, we exploit the difference between the Cherenkov and scintillation emission spectra and use dichroic filters to enhance the Cherenkov over scintillation ratio. Dichroic filters transmit or reflect photons based on their wavelength, with a photon attenuation lower than 10%. We investigate several shortpass and longpass dichroic filters in a single-photon configuration with BGO and find the optimal filter that maximizes the Cherenkov over scintillation ratio. We demonstrate that we can enhance the ratio of Cherenkov to scintillation photons by a factor of 2.17 ± 0.38 by employing a shortpass dichroic filter with a cut-off wavelength of 450 nm for BGO, and by a factor of 2.87 ± 0.40 using a longpass dichroic filter with a cut-on wavelength of 550 nm for iodine/beryllium-doped thallium chloride.

Science & Technology - Other Topics↗
DOE OSTI2024

New Ultrafast Scintillators with Core Valence Luminescence: Cs 2 MgCl 4 and Cs 3 MgCl 5

Future experiments in high energy physics and medical imaging require radiation detectors having properties which are not presently available. The main limitations arise from lack of suitable scintillation crystals. This dilemma prompts the need for research leading to the discovery of new fast and bright scintillator materials that combine unique properties to fulfil modern experiment requirements without compromises. In this work, single crystals of Cs 2 MgCl 4 and Cs 3 MgCl 5 up to 12 mm in diameter are grown via the vertical Bridgman method. Scintillation properties are reported for the first time, and core valence luminescence is observed for both compounds. X-ray excited radioluminescence emission of Cs 2 MgCl 4 is centered at 295 nm, with a scintillation decay time of 2.25 ± 0.05 ns and relatively high core-valence light yield of 2,200 ± 110 ph/MeV. Cs 3 MgCl 5 has two main emission peaks centered at 242 nm and 302 nm, decay time of 1.46 ± 0.05 ns, and light yield of 1,340 ± 70 ph/MeV. The better coincidence time resolution (CTR) is obtained with Cs 2 MgCl 4 , which is measured to be 129 ± 4 ps FWHM. Density functional theory (DFT) calculations are also performed and provide supporting evidence that the observed scintillation originates from core valence luminescence. Furthermore, the combination of speed and brightness of these new scintillators could be useful for fast timing applications in which moderately dense materials are required.

36 MATERIALS SCIENCE↗
DOE OSTI2024

MHD stability trends and improved performance of LHD inward-shifted configurations: The role of the neutral beam current drive and thermal plasma density

The aim of the present study is to analyze the effect of the neutral beam current drive (NBCD), thermal plasma density, and NBI operational regime on the stability of pressure gradient-driven modes (PGDM) and Alfvén eigenmodes (AE) in LHD inward-shifted configurations. The stabilization of n/m = 1/2 PGDM (n toroidal mode and m poloidal mode) is observed in the discharge 167 800 during the co-NBCD phase. The iota profile evolution measured by motional stark effect diagnostic may indicate the iota profile up-shift caused by the co-NBCD can induce a non-resonant transition of the rational surface 1/2 before the mode stabilization. The evolution of the iota profile and continuum gaps in the discharge 167 805 during the ctr-NBCD phase leads to the stabilization of the AE, caused by the narrowing of the continuum gap as the iota profile down-shift. Opposite stability trends are identified for PGDM and AE stability with respect to the thermal plasma density. A larger thermal plasma density (larger thermal β) further enhances PGDM although the continuum gaps are narrower leading to configurations with stable AEs. The linear stability of AEs is analyzed using the gyro-fluid FAR3d code to reproduce the AE stability trends observed in the experiments with respect to the NBCD and thermal plasma density. The analysis of hypothetical scenarios dedicated to study different NBI operational regimes with respect to EP energy, and β and radial density profiles indicate off-axis NBI operation shows a higher EP β threshold to destabilize AEs compared to on-axis configuration. This is explained by the presence of a TAE gap in the inner plasma region, easily destabilized by an on-axis NBI injection. The control of the NBCD and thermal plasma in the discharge 167 800 shows a transitory stabilization of PGDM and AEs, as well as an improved discharge performance identified by an increment of the neutron fluxes.

Varela, Jacobo↗
DOE OSTI2024

Scintillation and cherenkov photon counting detectors with analog silicon photomultipliers for TOF-PET

Objective. Standard signal processing approaches for scintillation detectors in positron emission tomography (PET) derive accurate estimates for 511 keV photon time of interaction and energy imparted to the detection media from aggregate characteristics of electronic pulse shapes. The ultimate realization of a scintillation detector for PET is one that provides a unique timestamp and position for each detected scintillation photon. Detectors with these capabilities enable advanced concepts for three-dimensional (3D) position and time of interaction estimation with methods that exploit the spatiotemporal arrival time kinetics of individual scintillation photons. Approach. In this work, we show that taking into consideration the temporal photon emission density of a scintillator, the channel density of an analog silicon photomultiplier (SiPM) array, and employing fast electronic readout with digital signal processing, a detector that counts and timestamps scintillation photons can be realized. To demonstrate this approach, a prototype detector was constructed, comprising multichannel electronic readout for a bismuth germanate (BGO) scintillator coupled to an SiPM array. Main Results. In proof-of-concept measurements with this detector, we were able to count and provide unique timestamps for 66% of all optical photons, where the remaining 34% (two-or-more-photon pulses) are also independently counted, but each photon bunch shares a common timestamp. We show this detector concept can implement 3D positioning of 511 keV photon interactions and thereby enable corrections for time of interaction estimators. The detector achieved 17.6% energy resolution at 511 keV and 237 ± 10 ps full-width-at-half-maximum coincidence time resolution (CTR) (fast spectral component) versus a reference detector. We outline the methodology, readout, and approach for achieving this detector capability in first-ever, proof-of-concept measurements for scintillation photon counting detector with analog silicon photomultipliers. Significance. The presented detector concept is a promising design for large area, high sensitivity TOF-PET detector modules that can implement advanced event positioning and time of interaction estimators, which could push state-of-the-art performance.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2022

Characterization of beam ion loss in high poloidal beta regime on EAST

A critical issue for achieving the integrated operation of steady-state long-pulse high-confinement (H-mode) plasmas on experimental advanced superconducting tokamak (EAST) is to improve beam ion population confinement during neutral beam injection (NBI). To study the characterization of beam ion loss and improve beam ion confinement, the steady-state long pulse scenario discharges were conducted on EAST (β p $\geqslant$ 2.0, β N $\geqslant$ 1.7, q 95 $\geqslant$ 6.7 and H 98y2 $\geqslant$ 1.1) with NBI heating. Based on neutron yield, the beam voltage and line-averaged electron density were adjusted from 50 kV to 60 kV and 4.4 × 10 19 m –3 to 5.0 × 10 19 m –3 , respectively. The results show that the dominant mechanisms of beam ion loss are shine-through loss, prompt loss, and stochastic ripple loss. The shine-through loss fraction is determined by initial velocity, flight time and entire beam path. The change in prompt loss fraction is caused by the change in the deposition of beam ions. The change in stochastic ripple loss fraction is caused by the change in the initial fraction of trapped-confined ions. Detailed physics shows that the prompt loss fraction during counter-Ip injections (~45%) is far larger than during co-Ip injections (~5%) due to the finite orbit width. The lost ions are mainly deposited on the lower divertor or below the midplane since the direction of magnetic drift is vertical down. The orbit types of prompt loss during counter-Ip injections are mainly trapped-lost and ctr-passing lost. To minimize the prompt loss fraction during counter-Ip injections, a reversed Ip configuration (rev-Ip) discharge #94758 was conducted. The result suggests that the beam ion wall load fraction during counter-Ip tangential injection (~3%) is far lower than that in normal Ip configuration (nor-Ip) discharge #94820. It is also found that the confinement of beam ion population in the counter-Ip injection #94758 was greatly improved when compared to #94820. Finally, this study can provide unique support for the improvement of beam ion population confinement and for the performance evaluation of the NBI system on EAST and future tokamaks.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2026

Counter-propagating toroidal Alfvén eigenmodes in tokamaks

Mechanisms of destabilization of toroidal Alfvén eigenmodes (TAEs) in tokamaks are analyzed with the aim to reveal those leading to modes propagating in the direction opposite to plasma current, i.e. counter-propagating modes (ctr-TAE). Plasmas with fast-ions sources [such as neutral beam injection (NBI), ion cyclotron resonance heating, fusion reactions] and without them (Ohmic discharges) are considered. A particular NSTX-U experiment with NBI, where co- and counter-propagating TAEs were observed simultaneously (Podestà et al 2018 Nucl. Fusion 58 082023), is considered. It is concluded that both types of TAEs occurred because their destabilization was caused by the velocity anisotropy of beam ions, which overrode effects of spatial inhomogeneity of these ions.

Alfvénic instabilities↗
DOE OSTI2020

Synthesis and Flash Sintering of (Hf1-xZrx)B2 Solid Solution Fine Powders

Fine powders of (Hf1-xZrx)B2 solid solution were synthesized by two methods. In the first one, solution-based processing of HfCl4, ZrCl4, sucrose and H3BO3 was carried out followed by heat treatment (e.g., at 1500 °C for 1 h) in Argon to achieve the carbothermal reduction (CTR) reaction to form the boride solid solution. In the second one, called boron hydride reduction (BHR) method, HfCl4, ZrCl4 and NaBH4 were directly mixed in a glove box followed by heat treatment in Argon at elevated temperatures from 700 to 1500 °C. In addition, the powders synthesized via both methods were flash sintered without sample preheating in a homemade setup. The synthesized powders as well as the flash sintered bulk ceramics were characterized using different techniques including XRD, SEM, EDS, TEM, TGA-DSC, and Vickers hardness test to reveal the inter-relationships between starting materials composition, processing conditions, and the resulting materials microstructure and physical/chemical properties.

Belisario, Jose↗