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DOE OSTI2023

Speciation and Reactivity Control of Cu-Oxo Clusters via Extraframework Al in Mordenite for Methane Oxidation

The stoichiometric conversion of methane to methanol by Cu-exchanged zeolites can be brought to highest yields by the presence of extraframework Al and high CH 4 chemical potentials. Here, combining theory and experiments, the differences in chemical reactivity of monometallic Cu-oxo and bimetallic Cu-Al-oxo nanoclusters stabilized in zeolite mordenite (MOR) are investigated. Cu-L 3 edge X-ray absorption near-edge structure (XANES), infrared (IR), and ultraviolet–visible (UV–vis) spectroscopies, in combination with CH 4 oxidation activity tests, support the presence of two types of active clusters in MOR and allow quantification of the relative proportions of each type in dependence of the Cu concentration. Ab initio molecular dynamics (MD) calculations and thermodynamic analyses indicate that the superior performance of materials enriched in Cu-Al-oxo clusters is related to the activity of two μ-oxo bridges in the cluster. Replacing H 2 O with ethanol in the product extraction step led to the formation of ethyl methyl ether, expanding this way the applicability of these materials for the activation and functionalization of CH 4 . We show that competition between different ion-exchanged metal-oxo structures during the synthesis of Cu-exchanged zeolites determines the formation of active species, and this provides guidelines for the synthesis of highly active materials for CH 4 activation and functionalization.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2026

Atomic Alignment in PbS Nanocrystal Superlattices with Compact Inorganic Ligands via Reversible Oriented Attachment of Nanocrystals

Nanocrystals (NCs) serve as versatile building blocks for the creation of functional materials with NC self-assembly offering opportunities to enable novel material properties. Here, in this work, we demonstrate that PbS NCs functionalized with strongly negatively charged metal chalcogenide complex (MCC) ligands, such as Sn 2 S 6 4– and AsS 4 3– , can self-assemble into all-inorganic superlattices with both long-range superlattice translational and atomic-lattice orientational order. Structural characterizations reveal that the NCs adopt an unexpected edge-to-edge alignment, and numerical simulation clarifies that orientational order is thermodynamically stabilized by many-body ion correlations originating from the dense electrolyte. Furthermore, we show that the superlattices of Sn 2 S 6 4– -functionalized PbS NCs can be fully disassembled back into the colloidal state, which is highly unusual for orientationally attached superlattices with atomic-lattice alignment. The reversible oriented attachment of NCs, enabling their dynamic assembly and disassembly into effectively single-crystalline superstructures, offers a pathway toward designing reconfigurable materials with adaptive and controllable electronic and optoelectronic properties.

Landau-Ginzburg theory↗

NASA NTRS1972

Pitch-angle diffusion of radiation belt electrons within the plasmasphere.

Study of the formation of the quiet-time electron slot, which divides the radiation belt electrons into an inner and an outer zone. The pitch-angle diffusion of radiation belt electrons resulting from resonant interactions with the observed plasmaspheric whistler-mode wave band is quantitatively investigated. The effects of wave propagation obliquely to the geomagnetic field direction with the resulting diffusion at all cyclotron-harmonic resonances and the Landau resonance are evaluated along with the effects of interactions occuring at all geomagnetic latitudes. The results obtained account for the long-term stability of the inner radiation zone, the location of its outer edge as a function of electron energy, and the removal of electrons to levels near zero throughout the slot. Computed pitch-angle distributions and precipitation decay rates are in good agreement with slot-region observations.

Lyons, L. R.↗

NASA NTRS1985

Long-term thermal aging of Celion/V378A composite materials

Celion 6000/V378A graphite/bismaleimide composite materials were aged in air at temperatures of 177, 204, 232 and 260 deg C for various times up to 15,000 hours. Three unidirectional specimen types were aged: short beam shear (SBS), flexure, and 153 mm square panels. Aged specimens of V378A laminates exhibited excellent thermal stability. Extensive cracking was observed during aging on the 0 deg edges of the unidirectional laminates. These cracks penetrated as deep as 12 mm from the edge. The cracking appeared to have little or no effect on the observed properties of the laminates. The study indicates that the useful life of unrestrained unidirectional graphite/V378A laminates is 10,000 hours or greater at 177 C to 232 C and 2,000 to 2,000 hour at 260 C.

Nelson, J. B.↗

NASA NTRS1989

Experimental Aerodynamic Characteristics of a Joined-wing Research Aircraft Configuration

A wind-tunnel test was conducted at Ames Research Center to measure the aerodynamic characteristics of a joined-wing research aircraft (JWRA). This aircraft was designed to utilize the fuselage and engines of the existing NASA AD-1 aircraft. The JWRA was designed to have removable outer wing panels to represent three different configurations with the interwing joint at different fractions of the wing span. A one-sixth-scale wind-tunnel model of all three configurations of the JWRA was tested in the Ames 12-Foot Pressure Wind Tunnel to measure aerodynamic performance, stability, and control characteristics. The results of these tests are presented. Longitudinal and lateral-directional characteristics were measured over an angle of attack range of -7 to 14 deg and over an angle of sideslip range of -5 to +2.5 deg at a Mach number of 0.35 and a Reynolds number of 2.2x10(6)/ft. Various combinations of deflected control surfaces were tested to measure the effectiveness and impact on stability of several control surface arrangements. In addition, the effects on stall and post-stall aerodynamic characteristics from small leading-edge devices called vortilons were measured. The results of these tests indicate that the JWRA had very good aerodynamic performance and acceptable stability and control throughout its flight envelope. The vortilons produced a profound improvement in the stall and post-stall characteristics with no measurable effects on cruise performance.

Smith, Stephen C.↗

NASA NTRS1988

Wave/current interaction model

The wave-current interaction for the application to remote sensing data via numerical simulations and data comparison is modelled. Using the field data of surface current shear, wind condition and ambient wave spectrum, the numerical simulations of directional wave spectrum evolution were used to interpret and to compare with the aircraft data from Radar Ocean Wave Spectrometer (ROWS) and Surface Contour Radar (SCR) across the front during Frontal Air Sea Interaction Experiment (FASINEX). The wave-ice interaction was inspired by the observation of large amplitude waves hundreds of kms inside the ice pack in the Weddell Sea, resulting in breakup of the ice pack. The developed analysis of processes includes the refraction of waves at the pack edge, the effects of pack compression on wave propagation, wave train stability and buckling stability in the ice pack. Sources of pack compression and interaction between wave momentum and pack compression are investigated. Viscous camping of propagating waves in the marginal ice zone are also studied. The analysis suggests an explanation for the change in wave dispersion observed from the ship and the sequence of processes that cause ice pack breakup, pressure ridge formation and the formation of open bands of water.

Liu, A. K.↗

NASA NTRS1956

Theoretical investigation of flutter of two-dimensional flat panels with one surface exposed to supersonic potential flow

A Rayleigh type analysis involving chosen modes of the panel as degrees of freedom is used to treat the flutter of a two-dimensional flat panel supported at its leading and trailing edges and subjected to a middle-plane tensile force. The panel has a supersonic stream passing over its upper surface and still air below. The aerodynamic forces due to the supersonic stream are obtained from the theory for linearized two-dimensional unsteady flow and the forces due to the still air are obtained from acoustical theory. In order to study the effect of increasing the number of modes in the analysis, two and then four modes are employed. The modes used are the first four natural modes of the panel in a vacuum with no tensile force acting. The analysis includes these variables: Mach number, structural damping, tensile force, density of the still air, and edge fixity (clamped and pinned). For certain combinations of these variables, stability boundaries are obtained which can be used to determine the panel thickness required to prevent flutter for any panel material and altitude.

Nelson, Herbert C↗

NASA NTRS2004

Unsteady Aerodynamic Response of a Linear Cascade of Airfoils in Separated Flow

The overall objective of this research program was to investigate methods to modify the leading edge separation region, which could lead to an improvement in aeroelastic stability of advanced airfoil designs. The airfoil section used is representative of current low aspect ratio fan blade tip sections. The experimental potion of this study investigated separated zone boundary layer from removal through suction slots. Suction applied to a cavity in the vicinity of the separation onset point was found to be the most effective location. The computational study looked into the influence of front camber on flutter stability. To assess the influence of the change in airfoil shape on stability the work-per-cycle was evaluated for torsion mode oscillations. It was shown that the front camberline shape can be an important factor for stabilizing the predicted work-per-cycle and reducing the predicted extent of the separation zone. In addition, data analysis procedures are discussed for reducing data acquired in experiments that involve periodic unsteady data. This work was conducted in support of experiments being conducted in the NASA Glenn Research Center Transonic Flutter Cascade. The spectral block averaging method is presented. This method is shown to be able to account for variations in airfoil oscillation frequency that can occur in experiments that force oscillate the airfoils to simulate flutter.

Capece, Vincent R.↗

NASA NTRS2011

Unstructured CFD Aerodynamic Analysis of a Generic UCAV Configuration

Three independent studies from the United States (NASA), Sweden (FOI), and Australia (DSTO) are analyzed to assess the state of current unstructured-grid computational fluid dynamic tools and practices for predicting the complex static and dynamic aerodynamic and stability characteristics of a generic 53-degree swept, round-leading-edge uninhabited combat air vehicle configuration, called SACCON. NASA exercised the USM3D tetrahedral cell-centered flow solver, while FOI and DSTO applied the FOI/EDGE general-cell vertex-based solver. The authors primarily employ the Reynolds Averaged Navier-Stokes (RANS) assumption, with a limited assessment of the EDGE Detached Eddy Simulation (DES) extension, to explore sensitivities to grids and turbulence models. Correlations with experimental data are provided for force and moments, surface pressure, and off-body flow measurements. The vortical flow field over SACCON proved extremely difficult to model adequately. As a general rule, the prospect of obtaining reasonable correlations of SACCON pitching moment characteristics with the RANS formulation is not promising, even for static cases. Yet, dynamic pitch oscillation results seem to produce a promising characterization of shapes for the lift and pitching moment hysteresis curves. Future studies of this configuration should include more investigation with higher-fidelity turbulence models, such as DES.

Frink, Neal T.↗

DOE OSTI2021

Type-I ELM mitigation by continuous lithium granule gravitational injection into the upper tungsten divertor in EAST

Large edge-localized modes (ELMs) were mitigated by gravitational injection of lithium granules into the upper X-point region of the experimental advanced superconducting tokamak (EAST) device with tungsten plasma-facing components. The maximum ELM size was reduced by ~70% in high β N H-mode plasmas. Large ELM stabilization was sustained for up to about 40 energy confinement times, with constant core radiated power and no evidence of high-Z or low-Z impurity accumulation. The lithium granules injection reduced the edge plasma pedestal density and temperature and their gradients, due to increased edge radiation and reduced recycling from the plasma-facing components. Ideal stability calculations using the ELITE code indicate that the stabilization of large ELMs correlates with improved stability of intermediate-n peeling-ballooning modes, due to reduced edge current resulting from the profile changes. The pedestal pressure reduction was partially offset by a core density increase, which resulted in a modest ~7% drop in core stored energy and normalized energy confinement time. We surmise that the remnant small ELMs are triggered by the penetration of multiple Li granules just past the separatrix, similar to small ELMs triggered by deuterium pellet Futatani et al (2014 Nucl. Fusion 54 073008). This study extends previous ELM elimination with Li powder injection Maingi et al (2018 Nucl. Fusion 58 024003) in EAST because (1) use of small, dust-like powder and the related potential health hazards were eliminated, and (2) use of macroscopic granules should be more applicable to future devices, due to deeper penetration than dust particles, e.g. inside the separatrix with velocities ~10 m s -1 in EAST.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS1989

Stability characteristics of a conical aerospace plane concept

Data on stability characteristics of a conical aerospace plane concept were collected for a number of model geometry variations and test conditions, using several NASA-Langley wind tunnels spanning Mach range 0.1-6. The baseline configuration of this plane concept incorporated a 5-deg cone forebody, a 75.96-deg delta wing, a 16-deg leading-edge sweep deployable canard, and a centerline vertical tail. The key results pertinent to stability considerations about all three axes of the model are presented together with data on the effect of the canard on pitch stability, the effect of vertical tail on lateral-directional stability, and the effect of forebody geometry on yaw asymmetries. The experimental stability data are compared with the results from an engineering predictive code.

Hahne, David E.↗

NASA NTRS1986

Wind-tunnel investigation of the flight characteristics of a canard general-aviation airplane configuration

A 0.36-scale model of a canard general-aviation airplane with a single pusher propeller and winglets was tested in the Langley 30- by 60-Foot Wind Tunnel to determine the static and dynamic stability and control and free-flight behavior of the configuration. Model variables made testing of the model possible with the canard in high and low positions, with increased winglet area, with outboard wing leading-edge droop, with fuselage-mounted vertical fin and rudder, with enlarged rudders, with dual deflecting rudders, and with ailerons mounted closer to the wing tips. The basic model exhibited generally good longitudinal and lateral stability and control characteristics. The removal of an outboard leading-edge droop degraded roll damping and produced lightly damped roll (wing rock) oscillations. In general, the model exhibited very stable dihedral effect but weak directional stability. Rudder and aileron control power were sufficiently adequate for control of most flight conditions, but appeared to be relatively weak for maneuvering compared with those of more conventionally configured models.

Satran, D. R.↗

DOE OSTI2025

Nanoscale Strain and Octahedral Tilting Removes Structural and Nonradiative Defects in 2D-Templated FAPbI 3

The halide perovskite formamidinium lead iodide (FAPbI 3 ) is a prime candidate for photovoltaics due to its excellent optoelectronic properties, but its application has been limited due to its structural instability. The large size of the FA cation results in metastability of the photoactive cubic phase and a facile degradation into thermodynamically stable hexagonal phases at room temperature. Recently, the incorporation of two-dimensional (2D) Ruddlesden-Popper halide perovskite seeds into a FAPbI 3 precursor solution was shown to template the growth of and stabilize cubic FAPbI 3 . Here, in this study, we investigate the nanoscale structural and optoelectronic mechanisms behind the observed bulk stabilization using synchrotron-based X-ray microscopies. Nanoprobe X-ray diffraction reveals 2D-templated FAPbI 3 films exhibit an average compressive strain normal to the substrate of -3.3%, 2-fold larger than that of MACl-stabilized FAPbI 3 . This compression creates locally templated regions composed of tetragonal-phase FAPbI 3 distributed nonuniformly throughout the film with fewer crystalline defects than purely cubic regions. Scanning X-ray excited optical luminescence (X-ray analog of photoluminescence) reveals that this local templating results in increased radiative recombination and red-shifted band edge and emission. Our results provide insight into the microscopic mechanism for the phase stabilization of FAPbI 3 using 2D perovskites as templates.

X-ray diffraction↗

DOE OSTI2020

Almost-Rigidity of Frameworks

Here, we extend the mathematical theory of rigidity of frameworks (graphs embedded in d-dimensional space) to consider nonlocal rigidity and flexibility properties. We provide conditions on a framework under which (I) as the framework flexes continuously it must remain inside a small ball, a property we call “almost-rigidity”; (II) any other framework with the same edge lengths must lie outside a much larger ball; (III) if the framework deforms by some given amount, its edge lengths change by a minimum amount; (IV) there is a nearby framework that is prestress stable, and thus rigid. The conditions can be tested efficiently using semidefinite programming. The test is a slight extension of the test for prestress stability of a framework, and gives analytic expressions for the radii of the balls and the edge length changes. Examples illustrate how the theory may be applied in practice, and we provide an algorithm to test for rigidity or almost-rigidity. We briefly discuss how the theory may be applied to tensegrities. © 2020 Wiley Periodicals LLC.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2025

Low- n stability and plasma response to RMP in various STEP scenarios

The low-n (n is the toroidal mode number) magnetohydrodynamic (MHD) stability and plasma response are numerically investigated for various scenarios designed for STEP, that are relevant for the H-mode pedestal analysis. Control of the edge-localized modes (ELMs) with externally applied resonant magnetic perturbations (RMPs) is considered. Optimization of the ELM control coil current configuration, based on the computed plasma MHD response and well-established figures of merit validated on present-day experiments, finds reasonable robustness of a fixed coil phasing (for a given n-number) to control ELMs in all five STEP plasmas considered. Based on certain semi-empirical criteria, the required coil current to achieve ELM suppression is estimated to be about 10–20 kAt with the n = 1 or 2 RMP configuration and about 100–200 kAt for the n = 4 RMP. Systematic linear stability calculations are used to map out stability windows for the low-n kink-peeling modes, in terms of the ideal-wall location and variation of the edge safety factor q 95 with respect to the target design. The kink-peeling stability boundary is found to be generally sensitive to the q 95 variation, which has implications for achieving the quiescent H-mode regime in STEP. Full toroidal quasilinear initial-value simulations for these STEP plasmas find that generation of the edge-harmonic oscillations (EHOs) depends sensitively on the plasma scenario, the initial linear stability of the kink-peeling modes, the initial plasma toroidal flow and q 95 . In general, it is easier (more robust) to access the EHO-regime for two of the cases considered with smaller plasma volume and higher on-axis safety factor. Finally, quasilinear simulations find robust density pumpout due to applied RMPs in these STEP plasmas, but the effect on the plasma toroidal flow varies among different cases.

EHO↗

NASA NTRS1981

Alleviation of Spin-Entry Tendencies through Localization of Wing-Flow Separation

Studies have been made on several wing leading-edge modifications applicable at present to single-engine light aircraft, which produce stabilizing vortices at stall and beyond. These vortices have the effect of fixing the stall pattern of the wing such that the various portions of the wing upper surface stall nearly symmetrically. The lift coefficient produced is maintained at a high level to angles of attack significantly above the stall angle of the unmodified wing, and the divergence in roll usually is reduced to a controllable level. It is hypothesized that these characteristics will help prevent inadvertent spin entry after a stall. Results are presented from recent large-scale wind-tunnel tests of a typical light aircraft, both with and without the modifications. The data indicate (hot the static stall and poststall characteristics of this aircraft, in a typical landing-approach condition, are noticeably improved when it suitable leading-edge modification is employed; and also that no appreciable aerodynamic penalties are evident in the normal flight envelope.

Feistel, T. W.↗

DOE OSTI2024

Correlation of the L-mode density limit with edge collisionality

The "density limit'' is one of the fundamental bounds on tokamak operating space, and is commonly estimated via the empirical Greenwald scaling. This limit has garnered renewed interest in recent years as it has become clear that ITER and many tokamak pilot plant concepts must operate near or above the widely-used Greenwald limit to achieve their objectives. Evidence has also grown that the Greenwald scaling - in its remarkable simplicity - may not capture the full complexity of the disruptive density limit. In this study, we assemble a multi-machine database to quantify the effectiveness of the Greenwald limit as a predictor of the L-mode density limit and identify alternative stability metrics. We find that a two-parameter dimensionless boundary in the plasma edge, $\nu_{*\rm, edge}^{\rm limit} = 3.0 \beta_{T,{\rm edge}}^{-0.4}$, achieves significantly higher accuracy (true negative rate of 97.7\% at a true positive rate of 95\%) than the Greenwald limit (true negative rate 86.1\% at a true positive rate of 95\%) across a multi-machine dataset including metal- and carbon-wall tokamaks (AUG, C-Mod, DIII-D, and TCV). The collisionality boundary presented here can be applied for density limit avoidance in current devices and in ITER, where it can be measured and responded to in real time.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS1986

Aerodynamic detuning analysis of an unstalled supersonic turbofan cascade

An approach to passive flutter control is aerodynamic detuning, defined as designed pasage-to-passage differences in the unsteady aerodynamic flow field of a rotor blade row. Thus, aerodynamic detuning directly affects the fundamental driving mechanism for flutter. A model to demonstrate the enhanced supersonic aeroelastic stability associated with aerodynamic detuning is developed. The stability of an aerodynamicaly detuned cascade operating in a supersonic inlet flow field with a subsonic leading edge locus analyzed, with the aerodynamic detuning accomplished by means of nonuniform circumferential spacing of adjacent rotor blades. The unsteady aerodynamic forces and moments on the blading are defined in terms of influence coefficients in a manner that permits the stability of both a conventional uniformally spaced rotor configuration as well as the detuned nonuniform circumferentialy spaced rotor to be determined. With Verdon's uniformly spaced Cascade B as a baseline, this analysis is then utilized to demonstrate the potential enhanced aeroelastic stability associated with this particular type of aerodynamic detuning.

Hoyniak, D.↗