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NASA NTRS2006

Experiments on the Motion of Drops on a Horizontal Solid Surface due to a Wettability Gradient

Results from experiments performed on the motion of drops of tetraethylene glycol in a wettability gradient present on a silicon surface are reported and compared with predictions from a recently developed theoretical model. The gradient in wettability was formed by exposing strips cut from a silicon wafer to decyltrichlorosiland vapors. Video images of the drops captured during the experiments were subsequently analyzed for drop size and velocity as functions of position along the gradient. In separate experiments on the same strips, the static contact angle formed by small drops was measured and used to obtain the local wettability gradient to which a drop is subjected. The velocity of the drops was found to be a strong function of position along the gradient. A quasi-steady theoretical model that balances the local hydrodynamic resistance with the local driving force generally describes the observations; possible reasons for the remaining discrepancies are discussed. It is shown that a model in which the driving force is reduced to accomodate the hysteresis effect inferred from the data is able to remove most of the discrepancy between the observed and predicted velocities.

Moumen, Nadjoua↗

DOE OSTI2018

Every Atom Counts: Elucidating the Fundamental Impact of Structural Change in Conjugated Polymers for Organic Photovoltaics

As many conjugated polymer-based organic photovoltaic (OPV) materials provide substantial solar power conversion efficiencies (as high as 13%), it is important to develop a deeper understanding of how the primary repeat unit structures impact device performance. In this work, we have varied the group 14 atom (C, Si, Ge) at the center of a bithiophene fused ring to elucidate the impact of a minimal repeat unit structure change on the optical, transport, and morphological properties, which ultimately control device performance. Careful polymerization and polymer purification produced three “one-atom change” donor–acceptor conjugated alternating copolymers with similar molecular weights and dispersities. DFT calculation, absorption spectroscopy, and high-temperature solution 1 H nuclear magnetic resonance (NMR) results indicate that poly(dithienosilole-alt-thienopyrrolodione), P(DTS-TPD), and poly(dithienogermole-alt-thienopyrrolodione), P(DTG-TPD) exhibit different rotational conformations when compared to poly(cyclopentadithiophene-alt-thienopyrrolodione), P(DTC-TPD). Solid-state 1 H MAS NMR experiments reveal that the greater probability of the anticonformation in P(DTS-TPD) and P(DTG-TPD) prevail in the solid phase. The conformational variation seen in solution and solid-state NMR in turn affects the polymer stacking and intermolecular interaction. Two-dimension 1 H- 1 H DQ-SQ NMR correlation spectra shows aromatic–aromatic correlations for P(DTS-TPD) and P(DTG-TPD), which on the other hand is absent for P(DTC-TPD). In a thin-film interchain packing study using grazing incidence wide-angle X-ray scattering (GIWAXS), we observe the π-face of the conjugated backbones of P(DTC-TPD) aligned edge-on to the substrate, whereas in contrast the π-faces of P(DTS-TPD) and P(DTG-TPD) align parallel to the surface. These differences in polymer conformations and backbone orientations lead to variations in the OPV performance of blends with the fullerene PC 71 BM, with the device containing P(DTC-TPD):PCBM having a lower fill factor and a lower power conversion efficiency. Ultrafast transient absorption spectroscopy shows the P(DTC-TPD):PCBM blend to have a more pronounced triplet formation from bimolecular recombination of initially separated charges. With a combination of sub-bandgap external quantum efficiency measurements and DFT calculations, we present evidence that the greater charge recombination loss is the result of a lower lying triplet energy level for P(DTC-TPD), leading to a higher rate of recombination and lower OPV device performance. In conclusion, importantly, this study ties ultimate photovoltaic performance to morphological features in the active films that are induced from the processing solution and are a result of minimal one-atom differences in polymer repeat unit structure.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Monomeric and Trimeric Thorium Chlorides Isolated from Acidic Aqueous Solution

Two thorium(IV) compounds, [Th(H 2 O) 4 Cl 4 ]·2 (HPy·Cl) ( 1 ) and (HPy) 3 [Th 3 (H 2 O) 2 Cl 10 (OH) 5 ]·4(HPy·Cl) ( 2 ) (HPy = pyridinium), were isolated from acidic aqueous solution. The compounds were synthesized at room temperature and subsequently characterized using single crystal X-ray diffraction along with Raman and IR spectroscopies. Whereas compound 1 is built from discrete mononuclear Th(H 2 O) 4 Cl 4 units, compound 2 consists of a novel hydroxo-bridged trimeric [Th 3 (OH) 5 ] 7+ core. Such species are largely absent from discussions of Th solution and solid-state chemistry and their isolation may be attributed to outer coordination sphere interactions that help stabilize the structural units; extensive hydrogen bonding and $π–π$ stacking interactions are present in 1 and 2 . Density functional theory calculations were performed to predict the respective vibrational frequencies of the structural units, and their relative stability was predicted at the correlated molecular theory level. Small-angle X-ray scattering analysis of [Th 3 (OH) 5 ] 7+ in water indicates that the trimeric structural unit remains intact and that it is indeed an important species that necessitates consideration in geochemical models and for design of Th materials from water.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Self-Assembly of a Midblock-Sulfonated Pentablock Copolymer in Mixed Organic Solvents: A Combined SAXS and SANS Analysis

Ionic, and specifically sulfonated, block copolymers are continually gaining interest in the soft materials community due to their unique suitability in various ion exchange applications such as fuel cells, organic photovoltaics, and desalination membranes. One unresolved challenge inherent to these materials is solvent templating, that is, the translation of self-assembled solution structures into non equilibrium solid film morphologies. Recently, the use of mixed polar/nonpolar organic solvents has been examined in an effort to elucidate and control the solution self-assembly of sulfonated block copolymers. The current study sheds new light on micellar assemblies (i.e., those with the sulfonated blocks comprising the micellar core) of a midblock-sulfonated pentablock copolymer in polar/nonpolar solvent mixtures by combining small-angle X-ray and small-angle neutron scattering. Our scattering data reveal that micelle size depends strongly on overall solvent composition: micelle cores and coronae grow as the fraction of nonpolar solvent is increased. Universal model fits further indicate that an unexpectedly high fraction of the micelle cores is occupied by polar solvent (60-80 vol %) and that partitioning of the polar solvent into micelle cores becomes more pronounced as its overall quantity decreases. This solvent presence in the micelle cores explains the simultaneous core/corona growth, which is otherwise counterintuitive. Furthermore our findings provide a potential pathway for the formation of solvent-templated films with more interconnected morphologies due to the greatly solvated micellar cores in solution, thereby enhancing the molecular, ion, and electron-transport properties of the resultant films.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2017

Phase Transition of H 2 in Subnanometer Pores Observed at 75 K

In this paper, we report a phase transition in H 2 adsorbed in a locally graphitic Saran carbon with subnanometer pores 0.5–0.65 nm in width, in which two layers of hydrogen can just barely squeeze, provided they pack tightly. The phase transition is observed at 75 K, temperatures far higher than other systems in which an adsorbent is known to increase phase transition temperatures: for instance, H 2 melts at 14 K in the bulk, but at 20 K on graphite because the solid H 2 is stabilized by the surface structure. Here we observe a transition at 75 K and 77–200 bar: from a low-temperature, low-density phase to a high-temperature, higher density phase. We model the low-density phase as a monolayer commensurate solid composed mostly of para-H 2 (the ground nuclear spin state, S = 0) and the high-density phase as an orientationally ordered bilayer commensurate solid composed mostly of ortho-H 2 (S = 1). We attribute the increase in density with temperature to the fact that the oblong ortho-H 2 can pack more densely. The transition is observed using two experiments. The high-density phase is associated with an increase in neutron backscatter by a factor of 7.0 ± 0.1. Normally, hydrogen produces no backscatter (scattering angle >90°). This backscatter appears along with a discontinuous increase in the excitation mass from 1.2 amu to 21.0 ± 2.3 amu, which we associate with collective nuclear spin excitations in the orientationally ordered phase. Film densities were measured using hydrogen adsorption. Finally, no phase transition was observed in H 2 adsorbed in control activated carbon materials.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Sheath constraints on turbulent magnetised plasmas

Abstract A solid target in contact with a plasma charges (negatively) to reflect the more mobile species (electrons) and thus keep the bulk plasma quasineutral. To shield the bulk plasma from the charged target, there is an oppositely (positively) charged sheath with a sharp electrostatic potential variation on the Debye length scale λ D . In magnetised plasmas where the magnetic field is inclined at an oblique angle α with the target, some of the sheath potential variation occurs also on the ion sound gyroradius length scale ρ S cos ⁡ α , caused by finite ion gyro-orbit distortion and losses. We consider a collisionless and steady-state magnetised plasma sheath whose thickness l ms ∼ max ( λ D , ρ S cos ⁡ α ) is smaller than the characteristic length scale L of spatial fluctuations in the bulk plasma, such that the limit l ms / L → 0 is appropriate. Spatial structures are assumed to be magnetic field-aligned. In the case of small magnetic field angle α ∼ δ ≡ ρ S / L ≪ 1 , electric fields tangential to the target transport ions towards the target via E × B drifts at a rate comparable to the one from parallel streaming. A generalised form of the kinetic Bohm–Chodura criterion at the sheath entrance is derived by requiring that the sheath electric field have a monotonic spatial decay far from the target. The criterion depends on tangential gradients of potential and ion distribution function, with additional nontrivial conditions.

kinetic Bohm–Chodura condition↗

NASA NTRS1973

Noise and wake structure measurements in a subsonic tip speed fan

The results of an experimental program are reported which show the effect of blade angle, tip speed, fan pressure ratio, and thrust on noise of a model fan of 0.457m (18 inches) diameter operating at subsonic tip speeds at pressure ratios between 1.06 and 1.15. The fan used in this study had 12 blades, 7 stator vanes, and a spacing between the rotor and stator of 1.85 blade chords. This fan was originally designed for aerodynamic testing and was considered a good performer. It was used in the noise test program as it incorporated features found to reduce noise in an earlier analytical parametric study. For a given pressure ratio the fan was shown to exhibit minimum noise at the blade angle and tip speed near that of maximum aerodynamic efficiency. Also, the noise level and spectrum character of this fan showed excellent correlation with scaled data of a similar larger diameter fan. Results of the program confirm the trends shown in the earlier analytical parametric study which showed that fan noise could be reduced for a given thrust and pressure ratio by increasing fan solidity, improving fan aerodynamic design, and operating the fan at an optimum subsonic tip speed. In addition to noise, the blade wake characteristics at the leading edge of the stator were measured in this program. At root and tip sections some difference between predicted and measured wakes was found. However comparisons between predicted and measured wakes at mid span locations was found to be good.

Magliozzi, B.↗

NASA NTRS1983

Test Report for MSFC Test No. 83-2: Pressure scaled water impact test of a 12.5 inch diameter model of the Space Shuttle solid rocket booster filament wound case and external TVC PCD

Water impact tests using a 12.5 inch diameter model representing a 8.56 percent scale of the Space Shuttle Solid Rocket Booster configuration were conducted. The two primary objectives of this SRB scale model water impact test program were: 1. Obtain cavity collapse applied pressure distributions for the 8.56 percent rigid body scale model FWC pressure magnitudes as a function of full-scale initial impact conditions at vertical velocities from 65 to 85 ft/sec, horizontal velocities from 0 to 45 ft/sec, and angles from -10 to +10 degrees. 2. Obtain rigid body applied pressures on the TVC pod and aft skirt internal stiffener rings at initial impact and cavity collapse loading events. In addition, nozzle loads were measured. Full scale vertical velocities of 65 to 85 ft/sec, horizontal velocities of 0 to 45 ft/sec, and impact angles from -10 to +10 degrees simulated.

Source record↗

NASA NTRS1989

Wide range magnetic electron spectrograph

An electron spectrogrpah is described that covers electron energies from 400 eV to 200 keV with an energy resolution of 10 percent. This overlaps the range of electrostatic deflection devices at low energy and solid state detectors at high energy. The spectrograph uses magnetic deflection of the electrons to achieve energy separation and images the full range of energies on a single plane. The magnetic circuit uses the fringing field of two axially located magnets to attain the large energy range. Six separate electron beams can be dispersed in the field, each entering the circuit from a different angle. This is a particular advantage when measuring plasma electron three-dimensional velocity distributions. The angular response of the instrument is particularly favorable and the stray magnetic field is sufficiently low to meet spacecraft requirements.

Coplan, M. A.↗

NASA NTRS2019

The Multi-Mission Earth Entry Vehicle for Sample Return Missions – Past, Present, and Future

The Multi-Mission Earth Entry Vehicle (MMEEV) is an enabling technology developed at NASA’s Langley Research Center (LaRC) over the last two decades for returning samples to Earth across a wide array of space science missions. Currently, the MMEEV is being considered for NASA’s Mars Sample Return (MSR) mission. The original vehicle concept, the Earth Entry Vehicle (EEV), was innovated at LaRC in 1998 as a robust solution to return Mars soil samples to Earth under stringent backward contamination requirements. These backward contamination requirements drove the EEV to have higher reliability than any capsule previously designed for a return-to-Earth sample return mission. The EEV achieved this high reliability by employing a passive (no active systems) vehicle architecture optimized for fault tolerance in a compact, low-mass configuration that is extensible to virtually any sample return mission. The original EEV concept utilized a carbon-carbon primary structure with high-density carbon phenolic thermal protection system. The capsule had a 60-degree sphere-cone forebody and a backshell geometry uniquely tailored to produce aerodynamics that would passively re-orient the vehicle if it entered the atmosphere with an off-nominal attitude. Contrary to every other sample return capsule conceived at the time, the EEV was designed to land without a parachute. The vehicle incorporated an integral energy-absorbing crushable structure that protected the Mars sample for landings on surfaces ranging from soft soil to solid concrete. This paper describes 20 years of technological advancements LaRC has incorporated into the EEV architecture to evolve it from the original, MSR-enabling vehicle, to a true multi-mission capability relevant to any sample return mission. The vehicle’s unique Integrated Composite Stiffener Structure (ICoSS) has been optimized for specific strength - supporting high-G atmospheric entries with steep entry angles that produce precise landing footprints on the ground. The vehicle geometry has been refined through wind tunnel testing and computational fluid dynamics simulations to improve the vehicle’s aerodynamic stability and robustness to off-nominal conditions from hypersonic to subsonic flight. The resulting configuration of the current MMEEV architecture is described, with details provided on its sample carrying capacity and atmospheric entry trajectory capabilities. The upgraded vehicle performance is mapped into current space science objectives, showing how the MMEEV supports future sample return missions and continues to be an enabling technology for NASA’s vision to return samples from Mars.

J M Corliss↗

DOE OSTI2023

INVESTIGATION OF ROCK-FLUID INTERACTIONS USING GEOMATERIAL MICROFLUIDICS

Illite and Illite-Smectite clays are reportedly the Caney Shale's most prevalent clay minerals. The swelling and fines migration of clays may occur when water-based fluids contact the clay minerals. This may result in the reduction of pore space and permeability, and wettability alteration. Therefore, we quantified the swelling potentials, fines migration and wettability alteration of Illite and Illite-Smectite clays upon exposure to model brines and a produced water, and a model oil and a crude oil. We measured density, viscosity, pH, TDS, and interfacial tension as they are important in multiphase flow and displacement characteristics. Geomaterial microfluidics is recently being used to study physicochemical interactions of solid-fluid systems. It facilitates visualizing the surface behavior upon exposure to various fluids. This study includes preparation and characterization of Illite-Smectite clay-coated glass capillary tubes. Illite and Illite-Smectite clay-coated geomaterial microfluidic surfaces were prepared to investigate the effects of first contact fluid, brine salinity, and aging on wettability. In this work, advancing and receding contact angles of model brine-air, model oil-air, produced water-air, crude oil-air, model brine-model oil systems, and produced water-crude oil systems have been measured in the untreated, and clay-coated microfluidic channels of 1000 µm width and 50 µm depth. The aging effect was studied by retaining the non-aqueous and aqueous solutions in the corresponding microfluidic channels for approximately 24 h in the case of channels first contacted by aqueous and non-aqueous solutions, respectively. The advancing and receding contact angles of Caney shale-crude oil-produced water systems were also measured. The experimental findings indicate the swelling potential, fines migration, and wettability alteration of Illite and Illite-Smectite clays. The results signify the influence of first contact fluid, brine salinity, and aging on wettability of the untreated and clay-coated microfluidic surfaces. The experiments also demonstrate the wetting nature of the Caney shale samples from reservoir and non-reservoir zones.

02 PETROLEUM↗

NASA NTRS1973

Space shuttle: Aerodynamic characteristics of a 162-inch diameter solid rocket booster with and without strakes

Tests conducted at NASA-Langley have shown that a small flap or strake can generate a significant amount of lift on a circular cylinder with large cross flow. If strakes are placed on the opposite sides and ends on a circular body, a moment will be produced about the center of mass of the body. The purpose of this test was to determine the static-aerodynamic forces and moments of a 162-inch diameter SRB (PRR) with and without strakes. The total angle-of-attack range of the SRB test was from -10 to 190 degrees. Model roll angles were 0, 45, 90, and 135 degrees with some intermediate angles. The Mach range was from 0.6 to 3.48. The 0.00494 scale model was designated as MSFC No. 449.

Johnson, J. D.↗

DOE OSTI2019

Assessment of impinged flame structure in high-pressure direct diesel injection

Spray impingement often occurs during cold-start in direct-injection diesel engines, affecting the subsequent combustion process by altering the local flow condition. This work has investigated the impinged flame structure by examining local expansion distance and planar curvature of the boundary in details. The experiments were carried out in a constant volume combustion chamber. The injection pressure and ambient density were varied from 120 to 180 MPa and 14.8 to 30.0 kg/m 3 under non-vaporizing conditions, respectively. For reacting conditions, the injection pressure and ambient density were fixed at 150 MPa and 22.8 kg/m 3 but with different ambient temperatures from 800 to 1000 K. Unlike orthogonal spray impingement, the profile of expansion distance along the radial direction at the 60° impinging angle is non-uniform but the profile is comparable between the non-vaporizing and reacting conditions under the same injection pressure and ambient density. With the help of Intensity-aXial-Time method, the most intensive soot luminosity region and Mie scattering intensity region are identified and the region has been found to be along the impinged spray axial direction. Outmost boundary of an impinged flame is found to have wrinkles attributed to air entrainment. The temporal level of flame wrinkles is higher in reacting conditions than in non-vaporizing conditions. The scatter distribution of the boundary curvature and near-field soot formation illustrates an inverted “S” shape correlation with time. High flame luminosity is found to be formed in concave regions while less soot is formed in convex regions. This inverted S-shape is a new finding of the state relationship at the solid–liquid–gas impinged flame propagation. Finally, heat flux measurement through the plate is examined.

Engineering↗

DOE OSTI2015

Transmission electron microscopy study of the MgS–Tm{sub 2}S{sub 3} system

This work presents the structural–microstructural characterization of the NaCl-derivative MgS–Tm{sub 2}S{sub 3} system, which can be formulated by the expression Mg{sub (1−x)}Tm{sub (2/3)x}□{sub (1/3)x}S (□→cation vacancy). Transmission electron microscopy observations show the transition between NaCl-type and spinel-type structures when 0 ≤x≤ 0.75. The increase of Tm content in the solid solution provokes the increase of the spinel-type phase proportion, which intergrows with the NaCl-type crystals. When x≥0.75, some phases derived from NaCl-type structure through the chemical twinning at the unit cell level crystallographic operation are observed, such as CT-MgTm{sub 2}S{sub 4} and CT-MgTm{sub 4}S{sub 7}. The existence and nature of the extended defects observed along the c direction of these structures are characterized by means of Scanning-Transmission electron microscopy high-angle dark field imaging, which allows observing the presence of quasi ordered crystals with new possible complex stoichiometries at atomic resolution. - Graphical abstract: HAADF-STEM image of a disordered CT-MgYb{sub 2}S{sub 4} crystal. The disordered twin-slab sequences are marked by arrows. - Highlights: • Structural evolution of the Mg{sub (1−x)}Tm{sub (2/3)x}□{sub (1/3)x}S system was characterized by means of TEM. • The increase in Tm content provokes the transition from NaCl to spinel-type structure up to x=0.75. • Chemical twinned phases CT-MgTm{sub 2}S{sub 4} and CT-MgTm{sub 4}S{sub 7} are observed at high Tm contents. • Extended defects in CT-crystals are characterized with atomic resolution STEM-HAADF images.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2012

Freezing in porous media: Phase behavior, dynamics and transport phenomena

This research was focused on developing the underlying framework for the mechanisms that control the nature of the solidification of a broad range of porous media. To encompass the scope of porous media under consideration we considered material ranging from a dilute colloidal suspension to a highly packed saturated host matrix with a known geometry. The basic physical processes that occur when the interstitial liquid phase solidifies revealed a host of surprises with a broad range of implications from geophysics to materials science and engineering. We now understand that ostensibly microscopic films of unfrozen liquid control both the equilibrium and transport properties of a highly packed saturated host matrix as well as a rather dilute colloidal suspension. However, our description of the effective medium behavior in these settings is rather different and this sets the stage for the future research based on our past results. Once the liquid phase of a saturated relatively densely packed material is frozen, there is a rich dynamical behavior of particles for example due to the directed motion driven by thermomolecular pressure gradients or the confined Brownian motion of the particles. In quite striking contrast, when one freezes a dilute suspension the behavior can be rather more like that of a binary alloy with the particles playing the role of a ``solute''. We probed such systems quantitatively by (i) using X ray photon correlation spectroscopy (XPCS) and Small Angle X-ray Scattering (SAXS) at the Advanced Photon Source at Argonne (ii) studying the Argonne cell in the laboratory using optical microscopy and imagery (because it is not directly visible while in the vacuum can). (3) analyzed the general transport phenomena within the framework of both irreversible thermodynamics and alloy solidification and (4) applied the results to the study of the redistribution of solid particles in a frozen interstitial material. This research has gone a long way towards establishing a quantitative foundation for a wide class of problems in environmental and technological settings.

54 ENVIRONMENTAL SCIENCES↗

NASA NTRS1977

An investigation to determine the static pressure distribution of the 0.00548 scale shuttle solid rocket booster (MSFC model number 468) during reentry in the NASA/MSFC 14 inch trisonic wind tunnel (SA28F)

The results of a pressure test of a .00548 scale 146 inch Space Shuttle Solid Rocket Booster (SRB) with and without protuberances, conducted in a 14 x 14 inch trisonic wind tunnel are presented. Static pressure distributions for the SRB at reentry attitudes and flight conditions were obtained. Local longitudinal and ring pressure distributions are presented in tabulated form. Integration of the pressure data was performed. The test was conducted at Mach numbers of 0.40 to 4.45 over an angle of attack range from 60 to 185 degrees. Roll angles of 0, 45, 90 and 315 degrees were investigated. Reynolds numbers per foot varied for selected Mach numbers.

Braddock, W. F.↗

NASA NTRS2018

Conceptual Aerodynamic Design of a Tail-Cone Thruster System Under Axi-Symmetric Inlet Distortion

This paper presents a conceptual design of a tail-cone thruster system which is operating under an axisymmetric inlet distortion. An effort to realize the targeted fuel burn saving that was proposed in NASA's STARC_ABL aircraft design is made through a CFD (Computational Fluid Dynamics)-based design approach. This method employs three iterative steps to exploit the CFD tools until the design requirements are met: a quasi-2D through-flow model to design the fan/EGV (Exit Guide Vane), a 3-D RANS (Reynolds Averaging Navier-Stokes) simulation of the single blade row to account for the inlet/fan and the EGV/nozzle interaction, and a 3-D RANS simulation of the airframe with a propulsor installed - propulsion airframe integration (PAI). The design requirements which include the thrust, and shaft power of the propulsor are matched throughout the evaluations coming from two CFD domains, i.e., the turbo-machinery and the PAI. During the switch between these different computational domains, the inlet and exit profiles are matched via the correction factors of the body-force model. The present tail-cone thruster (TCT) aerodynamic design leverages a low-pressure ratio fan (FPR=1.2 to approximately 1.25) of which the camber-line angles are predicted by a quasi-2D through-flow model. The quasi-2D model is derived to analyze the radially distorted flow resulting from the ingested boundary layer at the inlet. It also estimates the appropriate velocity vectors of the metal angles of the fan and EGV which is subjected to different types of vortex at the fan exit. The baseline geometry is revisited and its internal flow-path and exhaust cone are redesigned to illustrate the strong correlation among the components of the propulsor in the PAI domain. The peak efficiency point of the fan/EGV with respect to the blade counts, also known as solidity, and rotational speed is chosen for the cruise condition via parametric studies. The corresponding performance maps are presented. The resulting performance metrics of the new conceptual design of the BLI (Boundary Layer Ingestion) propulsor are analyzed and compared with these of the baseline in the PAI aspect. Finally, ideas of the CFD based design of a BLI propulsor are discussed based on the observations drawn from the numerical results.

Inlet↗

DOE OSTI2025

Crystal structure of Cu2Zn(GexSi1−x)Se4 solid solution: the kesterite to wurtz–kesterite structural phase transition

Developing low-cost, sustainable, and environmentally friendly top absorber layers for tandem solar cells is essential to advancing photovoltaic technologies and accelerating the transition to renewable energy. In this work, we explore the potential of tetravalent (Cu2Zn(GexSi1−x)Se4) cation mutations in chalcogenide compound semiconductors with the aim of finding a material with increased band gap and reduced structural disorder. A combination of high-resolution synchrotron powder diffraction and neutron powder diffraction was used to determine the atomic positions and monoclinic angles in monoclinic wurtz–kesterite type Cu2Zn(GexSi1−x)Se4 mixed crystals as well as to determine the cation distribution in the crystal structure of Ge-rich kesterite-type and Si-rich wurtz–kesterite type mixed crystals. These investigations enabled us to deduce the structural transition scenario within the Cu2Zn(GexSi1−x)Se4 series. The transition occurs via a region where two phases with different crystal structures, tetragonal and monoclinic and thus a different distortion of the coordination tetrahedra, but the same cation distribution within the element specific cation sites co-exist. Thus, the structural transition between the kesterite and the wurtz–kesterite structure within the Cu2Zn(GexSi1−x)Se4 series is a distortion driven transition. The study identifies cation mutation in quaternary chalcogenides as a promising strategy beyond chalcopyrites and kesterites for low cost and environmentally friendly top absorbers in tandem solar cells.

Gurieva, Galina [Helmholtz Center Berlin for Mater↗