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Results for “Conditional Normalizing Flow”

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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Computational hydrodynamics and optical performance of inductively-coupled plasma adaptive lenses

This study addresses the optical performance of a plasma adaptive lens for aero-optical applications by using both axisymmetric and three-dimensional numerical simulations. Plasma adaptive lenses are based on the effects of free electrons on the phase velocity of incident light, which, in theory, can be used as a phase-conjugation mechanism. A closed cylindrical chamber filled with Argon plasma is used as a model lens into which a beam of light is launched. The plasma is sustained by applying a radio-frequency electric current through a coil that envelops the chamber. Four different operating conditions, ranging from low to high powers and induction frequencies, are employed in the simulations. The numerical simulations reveal complex hydrodynamic phenomena related to buoyant and electromagnetic laminar transport, which generate, respectively, large recirculating cells and wall-normal compression stresses in the form of local stagnation-point flows. In the axisymmetric simulations, the plasma motion is coupled with near-wall axial striations in the electron-density field, some of which propagate in the form of low-frequency traveling disturbances adjacent to vortical quadrupoles that are reminiscent of Taylor-Görtler flow structures in centrifugally unstable flows. Although the refractive-index fields obtained from axisymmetric simulations lead to smooth beam wavefronts, they are found to be unstable to azimuthal disturbances in three of the four three-dimensional cases considered. The azimuthal striations are optically detrimental, since they produce high-order angular aberrations that account for most of the beam wavefront error. A fourth case is computed at high input power and high induction frequency, which displays the best optical properties among all the three-dimensional simulations considered. In particular, the increase in induction frequency prevents local thermalization and leads to an axisymmetric distribution of electrons even after introduction of spatial disturbances. The results highlight the importance of accounting for spatial effects in the numerical computations when optical analyses of plasma lenses are pursued in this range of operating conditions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Multiscale Aspects of the Storm Producing the June 2013 Flooding in Uttarakhand, India

Conditions producing disastrous flooding in Uttarakhand, India, in June 2013 differed from conditions that produced other notorious floods in the Himalayan region in recent years. During the week preceding the Uttarakhand flood, deep convection moistened the mountainsides, making them vulnerable to flooding. However, the precipitation producing the flood was not associated with a deep convective event. Rather, an eastward-propagating upper-level trough in the westerlies extended abnormally far southward, with the jet reaching the Himalayas. The south end of the trough merged with a monsoon low moving westward across India. The merged system produced persistent moist low-level flow oriented normal to the Himalayas that advected large amounts of water vapor into the Uttarakhand region. The flow was moist neutral when it passed over the Himalayan barrier, and orographic lifting produced heavy continuous rain over the region for 2–3 days. The precipitation was largely stratiform in nature although embedded convection of moderate depth occurred along the foothills, where some mild instability was being released. The Uttarakhand flood had characteristics in common with major 2013 floods in the Rocky Mountains in Colorado and Alberta, Canada.

Houze, R. A.↗
DOE OSTI2019

Coronary circulation: Pressure/flow parameters for assessment of ischemic heart disease

Both invasive and non-invasive parameters have been reported for assessment of the physiological status of the coronary circulation. Fractional flow reserve and coronary (or myocardial) flow reserve may be obtained by invasive or non-invasive means. These metrics of coronary stenosis severity have achieved wide clinical acceptance for guiding revascularization decisions and risk stratification. Other indices are obtained invasively (e.g., instantaneous wave-free ratio, iFR; hyperemic stenosis resistance) or non-invasively (e.g., PET absolute myocardial blood flow (mL/min/g)) and have been used for the same purposes. Both iFR, and whole-cycle distal coronary to aortic mean pressure (Pd/Pa) are measured under basal condition and used for assessment of hemodynamic stenosis severity as is index of basal stenosis resistance (BSR). These metrics typically are dichotomized at an empirically derived cut point into “normal” and “abnormal” categories for purposes of clinical decision making and data analysis. Once dichotomized the indices do not always point in the same direction and so confusion may arise. This review, therefore, will present basic principles relevant to understanding commonly employed metrics of the physiological status of the coronary circulation, potential strengths and weaknesses, and hopefully an improved appreciation of the clinical information provided by each.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2020

Performance Characterization of a Natural Gas–Air Rotating Detonation Engine

An experimental study of a rotating detonation engine (RDE) operating with natural gas and air at elevated chamber pressures and air preheat temperatures was conducted to quantify its performance at conditions representative of land-based power generation gas turbine engines. Here, the thrust produced by the combustor was measured to characterize its work output potential. High-frequency pressure transducers and broadband chemiluminescence measurements of the flame provided information about the wave structure and dynamics. Analysis of common performance metrics demonstrated the necessity of normalizing any RDE performance parameter by the driving system potential, typically the reactant manifold pressure. Application of a thermodynamic performance model to a generic RDE identified the area ratio between the RDE exhaust and injection throats as the primary parameter affecting delivered pressure gain. The model was further applied to draw comparison with experimental measurements of net pressure gain for identical flow conditions. Only one of the two tested injector configurations followed the predicted trends, suggesting that performance of the second was governed by physical processes other than the reactant thermodynamics. Although an absolute pressure gain was not demonstrated, it is promising that the natural gas–air RDE delivered up to 90% of the theoretical performance.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2018

Direct numerical simulations of premixed and stratified flame propagation in turbulent channel flow

Here, direct numerical simulations are performed to investigate the transient upstream flame propagation (flashback) through homogeneous and fuel-stratified hydrogen-air mixtures transported in fully developed turbulent channel flows. Results indicate that, for both cases, the flame maintains steady propagation against the bulk flow direction, and the global flame shape and the local flame characteristics are both affected by the occurrence of fuel stratification. Globally, the mean flame shape undergoes an abrupt change when the approaching reactants transition from an homogeneous to a stratified mixing configuration. A V-shaped flame surface, whose leading-edge is located in the near-wall region, characterizes the nonstratified, homogeneous mixture case, while a U-shaped flame surface, whose leading edge propagates upstream at the channel centerline, distinguishes the case with fuel stratification (fuel-lean in the near-wall region and fuel-rich away from the wall). The characteristic thickness, wrinkling, and displacement speed of the turbulent flame brush are subject to considerable changes across the channel due to the dependence of the turbulence and mixture properties on the distance from the channel walls. More specifically, the flame transitions from a moderately wrinkled, thin-flamelet combustion regime in the homogeneous mixture case to a strongly wrinkled flame brush more representative of a thickened-flame combustion regime in the near-wall region of the fuel-stratified case. The combustion regime may be related to the Karlovitz number, and it is shown that a nominal channel-flow Karlovitz number, Ka ch in , based on the wall-normal variation of canonical turbulence ( t η =(ν/ε) 1/2 ) and chemistry ( t l = δ l / S l ) timescales in fully developed channel flow, compares well with an effective Karlovitz number, Ka ch fl , extracted from the present DNS datasets using conditionally sampled values of t η and t l in the immediate vicinity of the flame (0.1 < C < 0.3).

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

The electrical characteristics of the dielectric barrier discharges

The electrical characteristics of the dielectric barrier discharges have been studied in this paper under different operating conditions. The dielectric barrier discharges were formed inside two reactors composed of electrodes in the shape of two parallel plates. The dielectric layers inside these reactors were pasted on the surface of one electrode only in the first reactor and on the surfaces of the two electrodes in the second reactor. The reactor under study has been fed by atmospheric air that flowed inside it with a constant rate at the normal temperature and pressure, in parallel with applying a sinusoidal ac voltage between the electrodes of the reactor. The amount of the electric charge that flows from the reactors to the external circuit has been studied experimentally versus the ac peak voltage applied to them. An analytical model has been obtained for calculating the electrical characteristics of the dielectric barrier discharges that were formed inside the reactors during a complete cycle of the ac voltage. The results that were calculated by using this model have agreed well with the experimental results under the different operating conditions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Effects of Hot Streak and Phantom Cooling on Heat Transfer in a Cooled Turbine Stage Including Particulate Deposition

The objective of this research effort was to develop a validated computational modeling capability for the characterization of the effects of hot streaks and particulate deposition on the heat load of modern gas turbines. This was accomplished with a multi-faceted approach including analytical, experimental, and computational components. A 1-year no cost extension request was approved for this effort, so the total duration was 4 years. The research effort succeeded in its ultimate objective by leveraging extensive experimental deposition studies complemented by computational modeling. Experiments were conducted with hot streaks, vane cooling, and combinations of hot streaks with vane cooling. These studies contributed to a significant body of corporate knowledge of deposition, in combination with particle rebound and deposition studies funded by other agencies, to provide suitable conditions for the development of a new model. The model includes the following physical phenomena: elastic deformation, plastic deformation, adhesion, and shear removal. It also incorporates material property sensitivity to temperature and tangential-normal velocity rebound cross-dependencies observed in experiments. The model is well-suited for incorporation in CFD simulations of complex gas turbine flows due to its algebraic (explicit) formulation. This report contains model predictions compared to coefficient of restitution data available in the open literature as well as deposition results from two different high temperature turbine deposition facilities. While the model comparisons with experiments are in many cases promising, several key aspects of particle deposition remain elusive. The simple phenomenological nature of the model allows for parametric dependencies to be evaluated in a straightforward manner. This effort also included the first-ever full turbine stage deposition model published in the open literature. The simulations included hot streaks and simulated vane cooling. The new deposition model was implemented into the CFD model as a wall boundary condition, with various particle sizes investigated in the simulation. Simulations utilizing a steady mixing plane formulation and an unsteady sliding mesh were conducted and the flow solution of each was validated against experimental data. Results from each of these simulations, including impact and capture distributions and efficiencies, were compared and potential reasons for differences discussed in detail. The inclusion of a large range of particle sizes allowed investigation of trends with particle size, such as increased radial migration and reduced sticking efficiency at the larger particle sizes. The unsteady simulation predicted lower sticking efficiencies on the rotor blades than the mixing plane simulation for the majority of particle sizes. This is postulated to be due to the preservation of the hot streak and cool vane wake through the vane-rotor interface (which are smeared out circumferentially in the mixing-plane simulation). The results reported here represent the successful implementation of a novel deposition model into validated vane-rotor flow solutions that include a non-uniform inlet temperature profile and simulated vane cooling.

42 ENGINEERING↗
DOE OSTI2019

Thermal Hydraulics of Helium-Cooled Finger-Type Divertors at Higher Incident Heat Fluxes

Over the last decade, a number of studies at the Georgia Institute of Technology (GT) have evaluated the thermal hydraulics of the design of the helium-cooled modular divertor with multiple jets (HEMJ) originally developed at the Karlsruhe Institute of Technology. Using the GT helium loop, a test section of a single HEMJ finger heated by a radio-frequency (rf) induction heater was studied at near prototypical condition at pressures of ~10 MPa, maximum mass flow rates of 8 g/s, and maximum helium inlet temperatures Ti of 425°C. The area-averaged cooled surface temperature was estimated from embedded thermocouple measurements. This, together with the average incident heat flux q &#x203E; &#x2032;&#x2032; , was used to determine the average heat transfer coefficient and the corresponding Nusselt number N u &#x203E; over the cooled surface. The normalized pressure loss coefficient KL was determined from the pressure drop measured across the test section. The helium loop was modified last year by enclosing the test section and heater within an argon-filled stainless steel chamber to minimize oxidation of the tungsten-alloy test section. Initial results, when extrapolated to prototypical conditions, suggested that N u &#x203E; was about 20% higher than our previous results. However, the maximum heat flux for these results was less than 3 MW/m2 due to rf coupling with the steel chamber walls. The chamber was then recently upgraded to a glass–stainless steel enclosure with modified feedthroughs for the induction heater connections to minimize this coupling. With this upgrade, a maximum incident heat flux q &#x203E; &#x2032;&#x2032; = 8.1 MW/m 2 was achieved. This work presents experimental estimates and correlations for N u &#x203E; and K L at higher heat fluxes. These results provide greater confidence when estimating the maximum heat flux that can be accommodated by the HEMJ at fully prototypical conditions. Lastly, preliminary metrology results for the test section used to experimentally study the simplified flat design variant of the HEMJ are presented as part of an effort to resolve recently reported discrepancies between experimentally estimated and numerically simulated N u &#x203E; .

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Investigation of particle–wall interaction in a pseudo-2D fluidized bed using CFD-DEM simulations

Here, we report on discrete element method simulations of a pseudo-two-dimensional (pseudo-2D) fluidized bed to investigate particle–wall interactions. Detailed information on macroscopic flow field variables, including solids pressure, granular temperature, and normal and tangential wall stresses are analyzed. The normal wall stress differs from the solids pressure because of the strong anisotropic flow behavior in the pseudo-2D system. A simple linear relationship exists between normal wall stress and solids pressure. In addition, an effective friction coefficient can be derived to characterize particle–wall flow interaction after evaluating the normal and tangential wall stresses. The effects of inter-particle and particle–wall friction coefficients are evaluated. Strong anisotropic flow behavior in the pseudo-2D system needs to be considered to validate the two-fluid model where the boundary condition is usually developed based on an isotropic assumption. The conclusion has been confirmed by simulation with different particle stiffnesses. Assumptions in the newly developed model for 2D simulation are further examined against the discrete element method simulation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Revisiting Johnson and Jackson boundary conditions for granular flows

In this article, we revisit Johnson and Jackson boundary conditions for granular flows. The oblique collision between a particle and a flat wall is analyzed by adopting the classic rigid-body theory and a more realistic semianalytical model. Based on the kinetic granular theory, the input parameter for the partial-slip boundary conditions, specularity coefficient, which is not measurable in experiments, is then interpreted as a function of the particle-wall restitution coefficient, the frictional coefficient, and the normalized slip velocity at the wall. An analytical expression for the specularity coefficient is suggested for a flat, frictional surface with a low frictional coefficient. The procedure for determining the specularity coefficient for a more general problem is outlined, and a working approximation is provided.

boundary condition↗
DOE OSTI2017

Micro-PIV measurements of multiphase flow of water and liquid CO 2 in 2-D heterogeneous porous micromodels

We present an experimental study of pore-scale flow dynamics of liquid CO 2 and water in a two-dimensional heterogeneous porous micromodel, inspired by the structure of a reservoir rock, at reservoir-relevant conditions (80 bar, 21°C). The entire process of CO 2 infiltration into a water-saturated micromodel was captured using fluorescence microscopy and the micro-PIV method, which together reveal complex fluid displacement patterns and abrupt changes in velocity. The CO 2 front migrated through the resident water in an intermittent manner, forming dendritic structures, termed fingers, in directions along, normal to, and even opposing the bulk pressure gradient. Such characteristics indicate the dominance of capillary fingering through the micromodel. Velocity burst events, termed Haines jumps, were also captured in the heterogeneous micromodel, during which the local Reynolds number was estimated to be ~21 in the CO 2 phase, exceeding the range of validity of Darcy's law. Furthermore, these drainage events were observed to be cooperative (i.e., across multiple pores simultaneously), with the zone of influence of such events extending beyond tens of pores, confirming, in a quantitative manner, that Haines jumps are nonlocal phenomena. After CO 2 completely breaks through the porous section, shear-induced circulations caused by flowing CO 2 were also observed, in agreement with previous studies using a homogeneous porous micromodel. To our knowledge, this study is the first quantitative measurement that incorporates both reservoir-relevant conditions and rock-inspired heterogeneity, and thus will be useful for pore-scale model development and validation.

42 ENGINEERING↗
DOE OSTI2012

ESBWR - Robust design for natural circulation and stability performance effectiveness

ESBWR is a 4500 MWt Generation III+ natural circulation reactor with an array of robust design features and passive safety systems to deliver highly effective plant performance during normal operation and to keep the reactor safe during postulated transients and accidents. With the submittal of the latest revision of the Design Control Document (DCD) to US Nuclear Regulatory Commission, ESBWR is nearing the completion of the US design certification process. This paper focuses on the natural circulation-driven plant performance aspects during normal operation, and stability evaluation of the robust ESBWR design. The TRACG computer code is used for the analysis of ESBWR plant performance, safety analysis, and stability margins. The paper describes the evaluation of ESBWR stability performance during normal power operation including operation in the Core Power-Feed Water Temperature Operating Domain. For ESBWR the normal power operation condition has the highest power/flow ratio and is limiting from the perspective of stability. The paper includes results from detailed evaluation of the most limiting decay ratio for out-of-phase regional oscillations calculated by perturbing the core inlet flow rate in this out-of-phase mode about the line of symmetry for the azimuthal harmonic mode. The paper also summarizes the ESBWR regional mode stability evaluations during a limiting transient (Loss of Feedwater Heating), and during ATWS (Anticipated Transient without Scram). Nominal decay ratios of limiting Channel oscillation, Core wide oscillation and Regional oscillation are within the maximum acceptance criterion of 0.8, at 95% content and 95% confidence. These stability evaluation results indicate decay ratio is within design limits. The paper also describes the evaluation of ESBWR stability performance during plant startup, and summarizes the defense-in-depth stability solution for ESBWR. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2012

Results from a scaled reactor cavity cooling system with water at steady state

We present a summary of steady-state experiments performed with a scaled, water-cooled Reactor Cavity Cooling System (RCCS) at the Univ. of Wisconsin - Madison. The RCCS concept is used for passive decay heat removal in the Next Generation Nuclear Plant (NGNP) design and was based on open literature of the GA-MHTGR, HTR-10 and AVR reactor. The RCCS is a 1/4 scale model of the full scale prototype system, with a 7.6 m structure housing, a 5 m tall test section, and 1,200 liter water storage tank. Radiant heaters impose a heat flux onto a three riser tube test section, representing a 5 deg. radial sector of the actual 360 deg. RCCS design. The maximum heat flux and power levels are 25 kW/m{sup 2} and 42.5 kW, and can be configured for variable, axial, or radial power profiles to simulate prototypic conditions. Experimental results yielded measurements of local surface temperatures, internal water temperatures, volumetric flow rates, and pressure drop along the test section and into the water storage tank. The majority of the tests achieved a steady state condition while remaining single-phase. A selected number of experiments were allowed to reach saturation and subsequently two-phase flow. RELAP5 simulations with the experimental data have been refined during test facility development and separate effects validation of the experimental facility. This test series represents the completion of our steady-state testing, with future experiments investigating normal and off-normal accident scenarios with two-phase flow effects. The ultimate goal of the project is to combine experimental data from UW - Madison, UI, ANL, and Texas A and M, with system model simulations to ascertain the feasibility of the RCCS as a successful long-term heat removal system during accident scenarios for the NGNP. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2013

Accuracy of State-of-the-Art Actuator-Line Modeling for Wind Turbine Wakes

The current actuator line method (ALM) within an OpenFOAM computational fluid dynamics (CFD) solver was used to perform simulations of the NREL Phase VI rotor under rotating and parked conditions, two fixed-wing designs both with an elliptic spanwise loading, and the NREL 5-MW turbine. The objective of this work is to assess and improve the accuracy of the state-of-the-art ALM in predicting rotor blade loads, particularly by focusing on the method used to project the actuator forces onto the flow field as body forces. Results obtained for sectional normal and tangential force coefficients were compared to available experimental data and to the in-house performance code XTurb-PSU. It was observed that the ALM results agree well with measured data and results obtained from XTurb-PSU except in the root and tip regions if a three-dimensional Gaussian of width, ε, constant along the blade span is used to project the actuator force onto the flow field. A new method is proposed where the Gaussian width, ε, varies along the blade span following an elliptic distribution. A general criterion is derived that applies to any planform shape. It is found that the new criterion for ε leads to improved prediction of blade tip loads for a variety of blade planforms and rotor conditions considered.

17 WIND ENERGY↗
DOE OSTI2016

Impacts of genetically engineered alterations in carbon sink pathways on photosynthetic performance

Genetic engineering of photosynthetic organisms typically redirects native metabolism towards desirable products, which thereby represent new metabolic sinks. There is limited information on how these modifications impact the evolved mechanisms of photosynthetic energy metabolism and cellular growth. Two engineered strains of Synechocystis sp. PCC 6803 with altered carbon sink capacity were assayed for their photosynthetic and CO 2 concentrating mechanism properties in conditions of high and low inorganic carbon (Ci) availability. In the ΔglgC mutant, glycogen cannot be synthesized and a carbon sink pathway has been effectively removed. The JU547 strain has been engineered by integration of the Pseudomonas syringae ethylene forming enzyme and provides a new sink. When cultured under high carbon conditions, ΔglgC displayed diminished photochemical efficiency, a more reduced NADPH pool, delayed initiation of the Calvin-Benson-Bassham cycle, and impairment of linear and cyclic electron flows. It also exhibited a large decrease in photochemical quenching indicative of the accumulation of Q A -, normally associated with a reduced PQ pool, but appears instead to be the result of an undefined dissipative mechanism to spill excess energy. In the case of carbon sink integration, JU547 displayed slightly more oxidized PQ and NADPH pools and increased rates of cyclic electron flow and an enhanced demand for inorganic carbon as suggested by increase in the expression of the bicarbonate transporter, SbtA. Overall, the results highlight the importance of the native regulatory network of autotrophic metabolism in governing photosynthetic performance and provide cogent examples of both predicable and difficult to predict phenotypic consequences upon installation of new pathways in autotrophs.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Resolved-particle simulation by the Physalis method: Enhancements and new capabilities

We present enhancements and new capabilities of the Physalis method for simulating disperse multiphase flows using particle-resolved simulation. The current work enhances the previous method by incorporating a new type of pressure-Poisson solver that couples with a new Physalis particle pressure boundary condition scheme and a new particle interior treatment to significantly improve overall numerical efficiency. Further, we implement a more efficient method of calculating the Physalis scalar products and incorporate short-range particle interaction models. We provide validation and benchmarking for the Physalis method against experiments of a sedimenting particle and of normal wall collisions. We conclude with an illustrative simulation of 2048 particles sedimenting in a duct. In the appendix, we present a complete and self-consistent description of the analytical development and numerical methods.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Migratory Behavior and Physiological Development as Potential Determinants of Life History Diversity in Fall Chinook Salmon in the Clearwater River

We studied the influence of behavior, water velocity, and physiological development on the downstream movement of subyearling fall Chinook Salmon Oncorhynchus tshawytscha in free-flowing and impounded reaches of the Clearwater and Snake rivers as potential mechanisms that might explain life history diversity in this stock. Movement rates and the percentage of radio-tagged fish that moved faster than the average current velocity were highest in the free-flowing Clearwater River compared to impounded reaches. This provided support for our hypothesis that water velocity is a primary determinant of downstream movement regardless of a fish’s physiological development. In contrast, movement rates slowed and detections became fewer in impounded reaches where velocities were much lower. The percentage of fish that moved faster than the average current velocity continued to decline and reached zero in the lower-most reach of Lower Granite Reservoir suggesting that behavioral disposition to move downstream was low. These findings contrast those of a similar, previous study of Snake River subyearlings in spite of hydrodynamic conditions being similar. Physiological differences between Snake and Clearwater river migrants shed light on this disparity. Subyearlings from the Clearwater River were parr-like in their development and never showed an increase in gill Na+/K+-ATPase activity as did smolts from the Snake River. The later emergence timing and cooler rearing temperatures in the Clearwater River may suppress normal physiological development that causes many fish to delay downstream movement and adopt a yearling life history strategy.

Tiffan, Kenneth F.↗