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NASA NTRS1980

Analytic investigation of efficiency and performance limits in klystron amplifiers using multidimensional computer programs; multi-stage depressed collectors; and thermionic cathode life studies

Due to complexity of the program which used a hydrodynamic, axially and radially deformable disk-ring model and the resulting long computing time only the output gap was investigated. Results from independent studies were used to initiate the starting conditions for the electrons and the RF voltage using our program. Although this method of computation is less exact than processing the entire klystron interaction in 3-Dimensions it is shown that, for a confined flow focused throughout the penultimate cavity, radial velocities remain very small and the beam is highly laminar. It is concluded that possible errors resulting from treating only the output cavity in 3-D would remain small.

Kosmahl, H. G.↗

DOE OSTI2021

Radiation Hydrodynamics in the Lagrangian Application Project’s LUMOS code

Starting in 2019, the Lagrangian Applications Project (LAP) and the Transport Project set out to develop a new ALE/Lagrangian radiation-hydrodynamics (RH) capability in a new code product named LUMOS. This work was done under the guidance of the Advanced Simulation and Computing (ASC) program with the goal of producing software capable of leveraging the high-order thermal radiative transfer (TRT) solvers provided by the Jayenne and Capsaicin software projects. This capability supplements the existing gray diffusion solver that is currently available in LAP’s FLAG code [1, 2, 3] for RH. The remainder of this memo describes the coupling of the radiation and hydrodynamics solvers within LAP’s LUMOS code. Initially delivered in 2020 as part of an L2 milestone [4], this capability continues to mature in FY21 with more efficient and robust algorithms, new support for ALE, and support for mixed materials per cell. Today, LUMOS is provided as a standard end-user product in the suite of LAP tools provided in each release cycle. Code access can be requested at https://asc.lanl.gov.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2020

First study of Hohlraum x-ray preheat asymmetry inside an ICF capsule

In indirect drive inertial confinement fusion (ICF), laser induced Hohlraum preheat radiation (so-called M-band, >1.8 keV) asymmetry will lead to asymmetric ablation front and ablator–fuel interface hydrodynamic instability growth in an imploding capsule. First experiments to infer the M-band asymmetries at the capsule were performed on the National Ignition Facility for high density carbon (HDC) ICF capsules in low density fill (0.3 mg/cc 4 He) Au Hohlraums by time resolved imaging of 2.3 keV fluorescence emission of a smaller Mo sphere placed inside the capsule. In this study, the measured Mo emission is pole hot (P 2 > 0) since M-band is generated mainly by the outer laser beams as their irradiance at the Hohlraum wall is 5× higher than for the inner beams. P 2 has a greater negative than positive swing vs time [Δ(P 2 /P 0 )/Δt ~ 0.2/ns], giving insight into laser heated Hohlraum dynamics. P 4 asymmetry is small at the sphere due to efficient geometric smoothing of Hohlraum asymmetries at large Hohlraum -to-capsule ratios. The M-band P 2 history is qualitatively reproduced by radiation hydrodynamic HYDRA simulations. The smaller P 2 than that calculated earlier suggests either less outer beam spot motion and/or preheat emission. At late times, the observed P 2 swing is larger and P 4 is more negative than simulated, which could be due to inner beams being stopped more in the outer beams wall plasma bubble than simulated. Asymmetry at the HDC capsule inner surface (“ice–ablator interface”) is also inferred from the Mo emission asymmetry by an analytic viewfactor model, accounting for the Mo/HDC radius difference and HDC capsule opacity.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2017

Effects of heat exchanger tubes on hydrodynamics and CO 2 capture of a sorbent-based fluidized bed reactor

In virtual design and scale up of pilot-scale carbon capture systems, the coupled reactive multiphase flow problem must be solved to predict the adsorber’s performance and capture efficiency under various operation conditions. This paper focuses on the detailed computational fluid dynamics (CFD) modeling of a pilot-scale fluidized bed adsorber equipped with vertical cooling tubes. Multiphase Flow with Interphase eXchanges (MFiX), an open-source multiphase flow CFD solver, is used for the simulations with custom code to simulate the chemical reactions and filtered models to capture the effect of the unresolved details in the coarser mesh for simulations with reasonable simulations and manageable computational effort. Previously developed two filtered models for horizontal cylinder drag, heat transfer, and reaction kinetics have been modified to derive the 2D filtered models representing vertical cylinders in the coarse-grid CFD simulations. The effects of the heat exchanger configurations (i.e., horizontal or vertical) on the adsorber’s hydrodynamics and CO2 capture performance are then examined. The simulation result subsequently is compared and contrasted with another predicted by a one-dimensional three-region process model.

bubbling bed↗

DOE OSTI2017

The Dynamics of Truncated Black Hole Accretion Disks. I. Viscous Hydrodynamic Case

Truncated accretion disks are commonly invoked to explain the spectro-temporal variability in accreting black holes in both small systems, i.e., state transitions in galactic black hole binaries (GBHBs), and large systems, i.e., low-luminosity active galactic nuclei (LLAGNs). In the canonical truncated disk model of moderately low accretion rate systems, gas in the inner region of the accretion disk occupies a hot, radiatively inefficient phase, which leads to a geometrically thick disk, while the gas in the outer region occupies a cooler, radiatively efficient phase that resides in the standard geometrically thin disk. Observationally, there is strong empirical evidence to support this phenomenological model, but a detailed understanding of the dynamics of truncated disks is lacking. We present a well-resolved viscous, hydrodynamic simulation that uses an ad hoc cooling prescription to drive a thermal instability and, hence, produce the first sustained truncated accretion disk. With this simulation, we perform a study of the dynamics, angular momentum transport, and energetics of a truncated disk. We find that the time variability introduced by the quasi-periodic transition of gas from efficient cooling to inefficient cooling impacts the evolution of the simulated disk. A consequence of the thermal instability is that an outflow is launched from the hot/cold gas interface, which drives large, sub-Keplerian convective cells into the disk atmosphere. The convective cells introduce a viscous θ − ϕ stress that is less than the generic r − ϕ viscous stress component, but greatly influences the evolution of the disk. In the truncated disk, we find that the bulk of the accreted gas is in the hot phase.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

Unifying the Micro and Macro Properties of AGN Feeding and Feedback

We unify the feeding and feedback of supermassive black holes with the global properties of galaxies, groups, and clusters by linking for the first time the physical mechanical efficiency at the horizon and megaparsec scale. The macro hot halo is tightly constrained by the absence of overheating and overcooling as probed by X-ray data and hydrodynamic simulations (ε{sub BH}≃10{sup −3} T{sub x,7.4}). The micro flow is shaped by general-relativistic effects tracked by state-of-the-art GR-RMHD simulations (ε{sub ∙}≃0.03). The supermassive black hole properties are tied to the X-ray halo temperature T{sub x}, or related cosmic scaling relation (as L{sub x}). The model is minimally based on first principles, such as conservation of energy and mass recycling. The inflow occurs via chaotic cold accretion (CCA), the rain of cold clouds condensing out of the quenched cooling flow and then recurrently funneled via inelastic collisions. Within 100s gravitational radii, the accretion energy is transformed into ultrafast 10{sup 4} km s{sup −1} outflows (UFOs) ejecting most of the inflowing mass. At larger radii, the energy-driven outflow entrains progressively more mass: at roughly kiloparsec scale, the velocities of the hot/warm/cold outflows are a few 10{sup 3}, 1000, and 500 km s{sup −1}, with median mass rates ∼ 10, 100, and several 100 M{sub ⊙} yr{sup −1}, respectively. The unified CCA model is consistent with the observations of nuclear UFOs and ionized, neutral, and molecular macro outflows. We provide step-by-step implementation for subgrid simulations, (semi)analytic works, or observational interpretations that require self-regulated AGN feedback at coarse scales, avoiding the a-posteriori fine-tuning of efficiencies.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

DYNAMICAL ACCRETION OF PRIMORDIAL ATMOSPHERES AROUND PLANETS WITH MASSES BETWEEN 0.1 AND 5 M {sub ⊕} IN THE HABITABLE ZONE

In the early, disk-embedded phase of evolution of terrestrial planets, a protoplanetary core can accumulate gas from the circumstellar disk into a planetary envelope. In order to relate the accumulation and structure of this primordial atmosphere to the thermal evolution of the planetary core, we calculated atmosphere models characterized by the surface temperature of the core. We considered cores with masses between 0.1 and 5 M {sub ⊕} situated in the habitable zone around a solar-like star. The time-dependent simulations in 1D-spherical symmetry include the hydrodynamics equations, gray radiative transport, and convective energy transport. Using an implicit time integration scheme, we can use large time steps and and thus efficiently cover evolutionary timescales. Our results show that planetary atmospheres, when considered with reference to a fixed core temperature, are not necessarily stable, and multiple solutions may exist for one core temperature. As the structure and properties of nebula-embedded planetary atmospheres are an inherently time-dependent problem, we calculated estimates for the amount of primordial atmosphere by simulating the accretion process of disk gas onto planetary cores and the subsequent evolution of the embedded atmospheres. The temperature of the planetary core is thereby determined from the computation of the internal energy budget of the core. For cores more massive than about one Earth mass, we obtain that a comparatively short duration of the disk-embedded phase (∼10{sup 5} years) is sufficient for the accumulation of significant amounts of hydrogen atmosphere that are unlikely to be removed by later atmospheric escape processes.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2024

Effect of Aggregation and Molecular Size on the Ice Nucleation Efficiency of Proteins

Aerosol acts as ice-nucleating particles (INPs) by catalyzing the formation of ice crystals in clouds at temperatures above the homogeneous nucleation threshold (-38 °C). In this study, we show that the immersion mode ice nucleation efficiency of the environmentally relevant protein, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), occurs at temperatures between -6.8 and -31.6 °C. Further, we suggest that this range is controlled by the RuBisCO concentration and protein aggregation. The warmest median nucleation temperature (-7.9 ± 0.8 °C) was associated with the highest concentration of RuBisCO (2 × 10 –1 mg mL –1 ) and large aggregates with a hydrodynamic diameter of ~10 3 nm. We investigated four additional chemically and structurally diverse proteins, plus the tripeptide glutathione, and found that each of them was a less effective INP than RuBisCO. Ice nucleation efficiency of the proteins was independent of the size (molecular weight) for the five proteins investigated in this study. In contrast to previous work, increasing the concentration and degree of aggregation did not universally increase ice nucleation efficiency. RuBisCO was the exception to this generalization, although the underlying molecular mechanism determining why aggregated RuBisCO is such an effective INP remains elusive.

54 ENVIRONMENTAL SCIENCES↗

NASA NTRS1988

Heat conduction in cooling flows

It has been suggested that electron conduction may significantly reduce the accretion rate (and star foramtion rate) for cooling flows in clusters of galaxies. A numerical hydrodynamics code was used to investigate the time behavior of cooling flows with conduction. The usual conduction coefficient is modified by an efficiency factor, mu, to realize the effects of tangled magnetic field lines. Two classes of models are considered, one where mu is independent of position and time, and one where inflow stretches the field lines and changes mu. In both cases, there is only a narrow range of initial conditions for mu in which the cluster accretion rate is reduced while a significant temperature gradient occurs. In the first case, no steady solution exists in which both conditions are met. In the second case, steady state solutions occur in which both conditions are met, but only for a narrow range of initial values where mu = 0.001.

Bregman, Joel N.↗

NASA NTRS2021

Neutral–neutral synthesis of organic molecules in cometary comae

Remote and in situ observations of cometary gases have revealed the presence of a wealth of complex organic molecules, including carbon chains, alcohols, imines, and the amino acid glycine. Such chemical complexity in cometary material implies that impacts by comets could have supplied reagents for prebiotic chemistry to young planetary surfaces. However, the assumption that some of the molecules observed in cometary comae at millimetre wavelengths originate from ices stored inside the nucleus has not yet been proven. In fact, the comae of moderately-active comets reach sufficient densities within a few thousand kilometres of the nucleus for an active (solar radiation-driven) photochemistry to ensue. Here, we present results from our latest chemical-hydrodynamic models incorporating an updated reaction network, and show that the commonly-observed HC3N (cyanoacetylene) and NH2CHO (formamide) molecules can be efficiently produced in cometary comae as a result of two-body, neutral–neutral, gas-phase reactions involving well-known coma species. In the presence of a near-nucleus distributed source of CN (similar to that observed by the Rosetta spacecraft at comet 67P), we find that sufficient HC3N and NH2CHO can be synthesized to match the abundances of these molecules observed previously in Oort cloud comets. The precise coma origins of these (and other) complex organic molecules can be verified through radio interferometric mapping observations, for example using the Atacama Large Millimeter/submillimeter Array.

Comets↗

DOE OSTI2017

Stripped Elliptical Galaxies as Probes of ICM Physics. III. Deep Chandra Observations of NGC 4552: Measuring the Viscosity of the Intracluster Medium

We present results from a deep (200 ks) Chandra observation of the early-type galaxy NGC 4552 (M89), which is falling into the Virgo cluster. Previous shallower X-ray observations of this galaxy showed a remnant gas core, a tail to the South of the galaxy, and twin “horns” attached to the northern edge of the gas core. In our deeper data, we detect a diffuse, low surface brightness extension to the previously known tail, and measure the temperature structure within the tail. We combine the deep Chandra data with archival XMM-Newton observations to put a strong upper limit on the diffuse emission of the tail out to a large distance (10× the radius of the remnant core) from the galaxy center. In our two previous papers, we presented the results of hydrodynamical simulations of ram pressure stripping specifically for M89 falling into the Virgo cluster and investigated the effect of intracluster medium (ICM) viscosity. In this paper, we compare our deep data with our specifically tailored simulations and conclude that the observed morphology of the stripped tail in NGC 4552 is most similar to the inviscid models. We conclude that, to the extent the transport processes can be simply modeled as a hydrodynamic viscosity, the ICM viscosity is negligible. More generally, any micro-scale description of the transport processes in the high- β plasma of the cluster ICM must be consistent with the efficient mixing observed in the stripped tail on macroscopic scales.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2026

Second-order wave excitation forces in WEC-Sim/MOST: Implementation, experimental validation, and code-to-code comparison

Accurate prediction of second-order hydrodynamic loads is essential for floating bodies, including floating offshore wind turbines, wave energy converters, and hybrid wind–wave platforms. These nonlinear effects, arising from both sum- and difference-frequency forcing, are critical for capturing key response characteristics but remain challenging to model efficiently. In this work, we extend the open-source Wave Energy Converter Simulator / MATLAB for Offshore Simulation Tool by implementing second-order wave excitation forces, supporting both the full Quadratic Transfer Function formulation and the Newman approximation. The full Quadratic Transfer Function method is used for all code-to-code comparisons and experimental validation, while the Newman approximation is provided as a computationally lighter alternative. To benchmark the new capability, we perform a code-to-code comparison with OpenFAST and OrcaFlex. We then validate the enhanced model using wave-tank measurements of a 1:96 scale DeepCwind semi-submersible, showing that second-order effects are required to reproduce platform motions. The implementation employs a computationally efficient pre-computation strategy for second-order wave excitation forces, reducing simulation cost while maintaining engineering accuracy. Overall, this work advances the tool as an open-source and versatile tool for modelling floating offshore renewable-energy systems requiring second-order hydrodynamic fidelity.

17 WIND ENERGY↗

DOE OSTI2016

The spiral wave instability induced by a giant planet. I. Particle stirring in the inner regions of protoplanetary disks

We have recently shown that spiral density waves propagating in accretion disks can undergo a parametric instability by resonantly coupling with and transferring energy into pairs of inertial waves (or inertial-gravity waves when buoyancy is important). In this paper, we perform inviscid three-dimensional global hydrodynamic simulations to examine the growth and consequence of this instability operating on the spiral waves driven by a Jupiter-mass planet in a protoplanetary disk. We find that the spiral waves are destabilized via the spiral wave instability (SWI), generating hydrodynamic turbulence and sustained radially alternating vertical flows that appear to be associated with long wavelength inertial modes. In the interval 0.3 R{sub p}⩽R⩽0.7R{sub p}, where R {sub p} denotes the semimajor axis of the planetary orbit (assumed to be 5 au), the estimated vertical diffusion rate associated with the turbulence is characterized by α{sub diff}∼ (0.2--1.2)×10{sup −2}. For the disk model considered here, the diffusion rate is such that particles with sizes up to several centimeters are vertically mixed within the first pressure scale height. This suggests that the instability of spiral waves launched by a giant planet can significantly disperse solid particles and trace chemical species from the midplane. In planet formation models where the continuous local production of chondrules/pebbles occurs over Myr timescales to provide a feedstock for pebble accretion onto these bodies, this stirring of solid particles may add a time constraint: planetary embryos and large asteroids have to form before a gas giant forms in the outer disk, otherwise the SWI will significantly decrease the chondrule/pebble accretion efficiency.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRSDate not supplied

Two-Phase Flow in Packed Beds, Filters and Orifices: Summary of Findings of the Packed Bed Reactor Experiment Onboard of the International Space Station

Understanding the hydrodynamics of adiabatic two-phase flows in packed bed reactors enables the optimization of chemical reaction rates and products that crucial in pharmaceuticals and energy production industries. Additionally, this understanding aids in designing more efficient and compact reactors and reducing space and resource requirements. Insights gained from studying and understanding such flows in microgravity contribute to advancements of space technologies and the enhancement of our capabilities for undertaking future long duration safe, and sustainable space exploration missions. The objective of the Packed Bed Reactor Experiment series (PBRE and PBRE-2) was to develop a fundamental understanding of the hydrodynamics of adiabatic two-phase flows through porous media in microgravity. This work provides a description of the PBRE fluid system and presents the highlights of the PBRE and PBRE-2 previously flown with different packings and operated onboard of the International Space Station Microgravity Science Glovebox (ISS-MSG). These highlights include flow patterns and two-phase pressure drop, and the impact of capillary effects on pressure drop at various gas and liquid flow rates. This work also presents preliminary results from the Packed Bed Reactor Experiment-Water Recovery Series (PBRE-WRS) recently flown with filters and orifices, which was also operated on the ISS-MSG. The objective of the experiment is to validate hydrodynamic models at a range of gas and liquid flow rates pertinent to the operation of these test articles. The microgravity environment allows for measurement and observation of aspects of fluid dynamics that are unique when compared to observations made in full or partial gravity environments.

ISS↗

DOE OSTI2018

Regional-scale analysis of karst underground flow deduced from tracing experiments: examples from carbonate aquifers in Malaga province, southern Spain

Tracer concentration data from field experiments conducted in several carbonate aquifers (Malaga province, southern Spain) were analyzed following a dual approach based on the graphical evaluation method (GEM) and solute transport modeling to decipher flow mechanisms in karst systems at regional scale. The results show that conduit system geometry and flow conditions are the principal factors influencing tracer migration through the examined karst flow routes. Solute transport is mainly controlled by longitudinal advection and dispersion throughout the conduit length, but also by flow partitioning between mobile and immobile fluid phases, while the matrix diffusion process appears to be less relevant. The simulation of tracer breakthrough curves (BTCs) suggests that diffuse and concentrated flow through the unsaturated zone can have equivalent transport properties under extreme recharge, with high flow velocities and efficient mixing due to the high hydraulic gradients generated. Tracer mobilization within the saturated zone under low flow conditions mainly depends on the hydrodynamics (rather than on the karst conduit development), which promote a lower longitudinal advection and retardation in the tracer migration, resulting in a marked tailing effect of BTCs. The analytical advection-dispersion equation better approximates the effective flow velocity and longitudinal dispersion estimations provided by the GEM, while the non-equilibrium transport model achieves a better adjustment of most asymmetric and long-tailed BTCs. The assessment of karst underground flow properties from tracing tests at regional scale can aid design of groundwater management and protection strategies, particularly in large hydrogeological systems (i.e. transboundary carbonate aquifers) and/or in poorly investigated ones.

58 GEOSCIENCES↗

DOE OSTI2021

Numerical and Analytical Modeling of Flow Partitioning in Partially Saturated Fracture Networks

Infiltration processes in fractured-porous media remain a crucial, yet not very well understood component of recharge and vulnerability assessment. Under partially-saturated conditions flows in fractures, percolating fracture networks, and fault zones contribute to the fastest spectrum of infiltration velocities via preferential pathways. Specifically, the partitioning dynamics at fracture intersections determine the magnitude of flow fragmentation into vertical and horizontal components and hence the bulk flow velocity and dispersion of fracture networks. In this work, we derive an approximate analytical solution for the partitioning process and validate it using smoothed particle hydrodynamics simulations. The developed transfer function is conceptually based on simulation results and laboratory experiments carried out in previous works. It allows to efficiently simulate flow through fracture networks with simple cubic structure and arbitrary number of fractures and aperture sizes via linear response theory and convolution of a given input signal. We derive a non-dimensional bulk flow velocity ($\widetilde{v}$) and dispersion coefficient ($\widetilde{D}$) to characterize fracture networks in terms of dimensionless horizontal and vertical time scales $\tau_m$ and $\tau_0$. The dispersion coefficient is shown to strongly depend on the horizontal time scale and converges towards a constant value of $0.08$ within reasonable fluid and geometrical parameter ranges, while the non-dimensional velocity exhibits a characteristic $\widetilde{v} \sim \tau_m^{-1/2}$ scaling. Given that hydraulic information is often only available at limited places within (fractured-porous) aquifer system, such as boreholes or springs, our study intends to provide a rudimentary analytical concept to potentially reconstruct internal fracture network geometries from external boundary information, e.g., the dispersive properties of discharge (groundwater level fluctuations).

42 ENGINEERING↗

DOE OSTI2022

Novel fabrication tools for dynamic compression targets with engineered voids using photolithography methods

Mesoscale imperfections, such as pores and voids, can strongly modify the properties and the mechanical response of materials under extreme conditions. Tracking the material response and microstructure evolution during void collapse is crucial for understanding its performance. In particular, imperfections in the ablator materials, such as voids, can limit the efficiency of the fusion reaction and ultimately hinder ignition. To characterize how voids influence the response of materials during dynamic loading and seed hydrodynamic instabilities, we, in this paper, have developed a tailored fabrication procedure for designer targets with voids at specific locations. Our procedure uses SU-8 as a proxy for the ablator materials and hollow silica microspheres as a proxy for voids and pores. By using photolithography to design the targets’ geometry, we demonstrate precise and highly reproducible placement of a single void within the sample, which is key for a detailed understanding of its behavior under shock compression. This fabrication technique will benefit high-repetition rate experiments at x-ray and laser facilities. Insight from shock compression experiments will provide benchmarks for the next generation of microphysics modeling.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2020

Low Mach number fluctuating hydrodynamics model for ionic liquids

We present a new mesoscale model for ionic liquids based on a low Mach number fluctuating hydrodynamics formulation for multicomponent charged species. The low Mach number approach eliminates sound waves from the fully compressible equations leading to a computationally efficient incompressible formulation. The model uses a Gibbs free energy functional that includes enthalpy of mixing, interfacial energy, and electrostatic contributions. These lead to a new fourth-order term in the mass equations and a reversible stress in the momentum equations. We calibrate our model using parameters for [DMPI+][F6P-], an extensively-studied room temperature ionic liquid (RTIL), and numerically demonstrate the formation of mesoscopic structuring at equilibrium in two and three dimensions. In simulations with electrode boundaries the measured double layer capacitance decreases with voltage, in agreement with theoretical predictions and experimental measurements for RTILs. Finally, we present a shear electroosmosis example to demonstrate that the methodology can be used to model electrokinetic flows.

42 ENGINEERING↗