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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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NASA NTRS2012

Effect of Inflow Boundary Conditions on Hovering Tilt-Rotor Flows

A study on the effect of inflow turbulence boundary conditions on the local flow on and around a body in flight has been carried out. The study has been carried out using OVERFLOW2 flow solver using the default Spalart-Allmaras turbulence model in OVERFLOW. Many OVERFLOW turbulent flow simulations have been reported using the SA-fv3 model1 over the years. The present study demonstrates that the turbulence levels imposed as a boundary condition (b.c.) in the far-field as implemented in OVERFLOW are not correct. In fact, very low level of turbulence at the far-field boundary as implemented in OVERFLOW results in the SA-fv3 model predicting transition-like profiles on a given body. By choosing sufficiently high levels of the Reynolds number of turbulence, Rt, as a boundary condition, this anomalous behavior of SA-fv3 model is eliminated. Since numerous papers using OVERFLOW have been presented in the literature including that by the author2 using low level of inflow turbulence, it will be beneficial to the CFD community at large and in particular to the OVERFLOW community to understand this effect of the inflow b.c. in the SA-fv3 model. Various results reported over the years in domains such as high-lift applications, drag prediction applications and rotorcraft flow applications can be revisited using the new turbulence inflow boundary condition prescription as suggested in this study. It has been demonstrated in the literature that the effect of inflow turbulence level on the downstream development of flow is too important to be ignored. Demonstrative results are shown and compared with experiment for the case of hovering XV-15 rotor flow at a tip Reynolds number of 4.9 x 10(exp 6) and Mach number of 0.69 in Figs. 1 and 2 below. Fig. 1(a,b) shows skin friction predictions at radial station of r/R = 0.28 corresponding to 5 different inflow boundary conditions obtained with the SA-fv3 model. As the inflow turbulence is increased monotonically, from a value of Rt = 0.1 to 100.0 as shown in Fig. 1, a fully developed turbulent skin friction profile is realized progressively as shown in Fig. 1(b). Similarly skin friction results shown in Fig. 2(a,b) corresponding to radial stations of r/R = 0.72 reinforce the postulate made here that as the inflow turbulence level is increased gradually, fully turbulent on-the-blade simulation is realized uniformly. In the full paper extensive results on skin friction, pressure and velocity profiles as well as the Figure of Merit will be presented and compared with experiment that will illustrate the substantial effect of the inflow boundary conditions on the development of hovering rotor flow downstream.

Kaul, Upender K.↗
DOE OSTI2021

Upregulation of PPPDE1 contributes to anorectal malformations via the mitochondrial apoptosis pathway during hindgut development in rats

Congenital anorectal malformations (ARMs) are among the most prominent deformities of the gastrointestinal tract; however, their precise aetiology remains obscure. Immunohistochemistry demonstrated that, in the ARM group, the PPPDE1-positive cells were widely distributed in the hindgut epithelial tissue from GD13 to GD16. Immunofluorescence revealed that most TUNEL-, Bax-, and Cytochrome C (Cyt C)-positive cells overlapped with PPPDE1-positive cells in the urorectal septum (URS). Western blotting and quantitative real-time RT-PCR revealed that PPPDE1 levels were significantly higher in the ARM group from GD13 to GD14 (p < 0.05). IEC-6 cells were transfected with PPPDE1 overexpression plasmid/NC (negative control) or si-PPPDE1/si-NC. Flow cytometry analysis and CCK-8 assay (used to detect apoptosis and proliferation, respectively), as well as western blotting, showed that the levels of PPPDE1 were positively correlated with the pro-apoptotic molecules Bax and Cyt C. Accordingly, aberrantly high expression of PPPDE1 caused a spatiotemporal imbalance in foetal rats with ARMs during hindgut development. Therefore, the upregulation of PPPDE1 may promote epithelial apoptosis and reduce proliferation in the hindgut via the mitochondrial apoptotic pathway. This could affect the fusion of the URS and cloacal membrane, ultimately inhibiting the hindgut development and resulting in ARMs.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

Scalar mixing in a Kelvin-Helmholtz shear layer and implications for Reynolds-averaged Navier-Stokes modeling of mixing layers

Large-eddy simulation of a temporally evolving Kelvin-Helmholtz (KH) mixing layer is performed with the tenth-order compact difference code miranda to examine the steady-state behavior of a passive scalar in a shear-driven mixing layer. It is shown that the integral behavior of scalar variance in a KH mixing layer behaves similarly to the integral behavior of scalar variance in a Rayleigh-Taylor (RT) mixing layer, and mixedness of the simulated KH shear layer tends towards a value of about 0.8. It is further shown that if the k-L-a-V Reynolds-averaged Navier-Stokes (RANS) model [B. E. Morgan et al., Phys. Rev. E 98, 033111 (2018)], calibrated to reproduce steady-state mixing in an RT layer, is applied to simulate a KH mixing layer, the RANS model will significantly overpredict the magnitude of scalar variance in the KH layer. A straightforward addition to the k-L-a-V model is then suggested, and self-similarity analysis is applied to determine constraints on model coefficients. Furthermore, it is shown that with the addition of a buoyancy production term in the model equation for scalar variance, it becomes possible to eliminate the model deficiency and match steady-state mixedness in simulations of both RT and KH mixing layers with a single model calibration.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Measuring scale-dependent shape anisotropy by coarse-graining: Application to inhomogeneous Rayleigh-Taylor turbulence

Here, we generalize the “filtering spectrum” to probe scales along different directions by spatial coarse-graining. This multidimensional filtering spectrum quantifies the spectral content of flows that are not necessarily homogeneous. From multidimensional spectral information, we propose a simple metric for shape anisotropy at various scales. The method is applied to simulations of two-dimensional (2D) and 3D Rayleigh-Taylor (RT) turbulence, which is inhomogeneous and anisotropic. We show that 3D RT has clear shape anisotropy at large scales with approximately 4:3 vertical to horizontal aspect ratio but tends toward isotropy at small scales as expected. In sharp contrast, we find that RT in 2D simulations, which are still the main modeling framework for many applications, is isotropic at large scales and its shape anisotropy increases at smaller scales where structures tend to be horizontally elongated. While this may be surprising, it is consistent with recent results that large-scale isotropy in 2D RT is due to the generation of a large-scale overturning circulation via an upscale cascade, while small-scale anisotropy is due to the stable stratification resultant from such overturning and the inefficient mixing in 2D.

42 ENGINEERING↗
NASA NTRS1990

Influence of airfoil nose radius on sound generated by gust interactions

The sound radiated by interaction of a short wavelength gust (k much greater than 1) with a symmetric thin airfoil is analyzed. The theory is based on a linearization of the Euler equations about the subsonic mean flow past the airfoil. The sound generation mechanism is found to be concentrated in a local region surrounding the parabolic nose of the airfoil; the size of this local region scales on the gust wavelength. Airfoil thickness produces terms of relative order O(sq rt S) in the far field sound, where S is a Strouhal number based on the airfoil nose radius. At low Mach numbers, entropy gusts generate much less sound than vorticity gusts. However, for O(1) Mach numbers and moderate values of S, entropy and vorticity gusts produce similar sound levels.

Tsai, C. T.↗
DOE OSTI2021

ANGPTL4 regulates CD163 expression and Kuppfer cell polarization induced cirrhosis via TLR4/NF-κB pathway

Angiopoietin like 4 (ANGPTL4) has been proved to play an important role in lipid and glucose metabolism disorders and related cardiovascular diseases, but its role in the formation of cirrhosis still needs to be further explored. Therefore, the aim of this study was to investigate the role of ANGPTL4 in the development of liver cirrhosis and its mechanism, as well as its effect on Kupffer cell polarization and hepatic stellate cell activation. The ELISA and RT-qPCR assay were used to detect the content of ANGPTL4 in serum and mRNA expression in cells and tissues respectively. The expression of ANGPTL4, Arg1 and Mrc2 in Kupffer cells was measured by Western blot. The percentage of CD163{sup +} and CD206{sup +} cells was measured by flow cytometry. Mice cirrhosis model was established, and the expression of ANGPTL4 was interfered by injecting sh-ANGPTL4 lentiviral vector into caudal vein. The results revealed that ANGPTL4 was significantly up-regulated in liver cirrhosis patients and HBV induced liver injury cell models. Further studies found that interference with ANGPTL4 regulated CD163 and inhibited the polarization and proinflammatory effects of KCsas well as inhibited the activation of hepatic stellate cells (HSCs) and fibrosis. More importantly, Interference with ANGPTL4 inhibits the progression of liver cirrhosis in mice. What's more, TLR4/NF-κB pathway was involved in the molecular mechanism of ANGPTL4 on Kupffer cells and hepatic stellate cells. It is suggested that the mechanism of sh-ANGPTL4 suppressing the polarization of KCs and the activation of hepatic stellate cells (HSCs) is to regulate the TLR4/NF-κB signaling pathways.

60 APPLIED LIFE SCIENCES↗
NASA NTRS1995

Critical point of the solar wind by radio sounding data

Results of the close-to-Sun plasmas sounding at the transonic region of the solar wind, where the sub-to supersonic flow transition proceeds (at 10 to 40 solar radii from the Sun), are presented. Natural sources of two types were used, water vapour maser sources at 1.35 cm and guasars at 2.9 m wavelength. scattering observations cover the period of 1986 to 1993, Russian Academy of Sciences telescopes RT-22 and DCR-1000 were used, IPS index and scattering angle being the immediate results of observations. Extensive studies of the scintillation index and scattering angle radial profiles reveal a remarkable structural detail, 'transonic region forrunner'-narrow region of diminished scattering close to the internal border of the extended transonic region with its characteristic enhanced scattering. Comparisons of the scattering and plasma velocity profiles let it possible to determine the critical point positions by the comparatively simple scattering observations. This new possibility widely improves the process of the basic data accumulation in the fundamental problem of the solar wind acceleration mechanism.

Lotova, N. A.↗
DOE OSTI2020

Rayleigh-Taylor Instability: A Status Review of Experimental Designs and Measurement Diagnostics

The focus of experiments and the sophistication of diagnostics employed in Rayleigh-Taylor instability (RTI) induced mixing studies have evolved considerably over the past seven decades. The first theoretical analysis by Taylor and the two-dimensional experimental results by Lewis on RTI in 1950 examined single-mode RTI using conventional imaging techniques. Over the next 70 years, several experimental designs have been used to creating an RTI unstable interface between two materials of different densities. These early experiments though innovative, were arduous to diagnose and provided little information on the internal, turbulent structure and initial conditions of the RT mixing layer. Coupled with the availability of high-fidelity diagnostics, the experiments designed and developed in the last three decades allow detailed measurements of various turbulence statistics that have allowed broadly to validate and verify late-time nonlinear models and mix-models for buoyancy-driven flows. Besides, they have provided valuable insights to solve several long-standing disagreements in the field. Herein, this review serves as an opportunity to discuss the understanding of the RTI problem and highlight valuable insights gained into the RTI driven mixing process with a focus on low to high Atwood number (> 0.1) experiments.

42 ENGINEERING↗
DOE OSTI2021

Partially averaged Navier-Stokes closure modeling for variable-density turbulent flow

We report this work extends the framework of the partially averaged Navier-Stokes (PANS) equations to variable-density flow, i.e., multimaterial and/or compressible mixing problems with density variations and production of turbulence kinetic energy by both shear and buoyancy mechanisms. The proposed methodology is utilized to derive the PANS BHR-LEVM closure. This includes a priori testing to analyze and develop guidelines toward the efficient selection of the parameters controlling the physical resolution and, consequently, the range of resolved scales of PANS. Two archetypal test-cases involving transient turbulence, hydrodynamic instabilities, and coherent structures are used to illustrate the accuracy and potential of the method: the Taylor-Green vortex at Reynolds number Re = 3000, and the Rayleigh-Taylor flow at Atwood number 0.5 and (Re) max ≈ 500. These representative problems, for which turbulence is generated by shear and buoyancy processes, constitute the initial validation space of the new model, and their results are comprehensively discussed in two subsequent studies. The computations indicate that PANS can accurately predict the selected flow problems, resolving only a fraction of the scales of large-eddy simulation and direct numerical simulation strategies. The results also reiterate that the physical resolution of the PANS model must guarantee that the key instabilities and coherent structures of the flow are resolved. The remaining scales can be modeled through an adequate turbulence scale-dependent closure.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2003

Hypergravity Stimulates Osteoblast Proliferation Via Matrix-Integrin-Signaling Pathways

Extensive characterizations of the physiologic consequences of microgravity and gravity indicate that lack of weight-bearing may cause tissue atrophy through cellular and subcellular level mechanisms. We hypothesize that gravity is needed for the efficient transduction of cell growth and survival signals from the extra-cellular matrix (ECM) in mechanosensitive tissues. Recent work from our laboratory and from others shows that an increase of gravity increases bone cell growth and survival. We found that 50-g hypergravity stimulation increased osteoblast proliferation for cells grown on Collagen Type I and Fibronectin, but not on Laminin or uncoated plastic. This may be a tissue-specific response, because 50-g hypergravity stimulation caused no increase in proliferation for primary rat fibroblasts. These results combined with RT-PCR for all possible integrins indicate that beta1 integrin subunit may be involved. The osteoblast proliferation response on Collagen Type I was greater at 25-g than at 10-g or 50-g; 24-h duration of hypergravity was necessary to see an increase in proliferation. Survival was enhanced during hypergravity stimulation by the presence of matrix. Flow cytometry analysis indicated that cell cycle may be altered; BrdU incorporation in proliferating cells showed an increase in the number of actively dividing cells from about 60% at 1-g to over 90% at 25-g. To further investigate the molecular components involved, we applied fluorescence labeling of cytoskeletal and signaling molecules to cells after 2 to 30 minutes of hypergravity stimulation. While structural components did not appear to be altered, phosphorylation increased, indicating that signaling pathways may be activated. These data indicate that gravity mechanostimulation of osteoblast proliferation involves specific matrix-integrin signaling pathways which are sensitive to duration and g-level.

Vercoutere, W.↗
NASA NTRS1988

Initial adhesive screening of novel polyamide-imides and their copolymers

Continued interest by the research community in thermally stable, tough, high temperature adhesives has resulted in the investigation by Langley Research Center of two linear aromatic polyamide-imide (PAI) homopolymers and two linear aromatic PAI copolymers. The homopolymers were made with either 3,3'=DABA or 4,4'-DABA and BTDA. The two polymers were prepared with a monomer ratio of 0.75 DABP:0.25 DABA:1.00 BTDA. These aromatic PAIs possess high thermal stability because of intermolecular hydrogen bonding and chain stiffness. Lap shear strength (LSS) was the main criteria used to evaluate the polymers as adhesives. LSS of bonded Ti-6Al-4V was determined at room temperature (RT), 177, 204 and 232 C. The glass transition temperature and the type of bond failure were also determined. The best LSS values of the four adhesive systems investigated were obtained with the PAI copolymer identified in the report as LARC-TPI (25 percent 3,3'-DABA); however, it did not produce LSSs nearly as high as LARC-TPI. The poor flow properties observed appear to be due to a combination of high molecular weight and the increased interchain electronic interactions associated with the amide group.

Donald J Progar↗
NASA NTRS1989

Initial evaluation of novel polyamide-imides and their copolymers as adhesives

Continued interest by the research community in thermally stable, tough, high temperature adhesives has resulted in the investigation by Langley Research Center of two linear aromatic polyamide-imide (PAI) homopolymers and two linear aromatic PAI copolymers. The homopolymers were made with either 3,3'=DABA or 4,4'-DABA and BTDA. The two polymers were prepared with a monomer ratio of 0.75 DABP:0.25 DABA:1.00 BTDA. These aromatic PAIs possess high thermal stability because of intermolecular hydrogen bonding and chain stiffness. Lap shear strength (LSS) was the main criteria used to evaluate the polymers as adhesives. LSS of bonded Ti-6Al-4V was determined at room temperature (RT), 177, 204 and 232 C. The glass transition temperature and the type of bond failure were also determined. The best LSS values of the four adhesive systems investigated were obtained with the PAI copolymer identified in the report as LARC-TPI (25 percent 3,3'-DABA); however, it did not produce LSSs nearly as high as LARC-TPI. The poor flow properties observed appear to be due to a combination of high molecular weight and the increased interchain electronic interactions associated with the amide group.

Progar, Donald J.↗
DOE OSTI2023

Nonlinear ablative Rayleigh-Taylor instability: Increased growth due to self-generated magnetic fields

The growth rate of the nonlinear ablative Rayleigh-Taylor (RT) instability is enhanced by magnetic fields self-generated by the Biermann battery mechanism; a scaling for this effect with perturbation height and wavelength is proposed and validated with extended-magnetohydrodynamic simulations. The magnetic flux generation rate around a single RT spike is found to scale with the spike height. The Hall parameter, which quantifies electron magnetization, is found to be strongly enhanced for short-wavelength spikes due to Nernst compression of the magnetic field at the spike tip. Furthermore, the impact of the magnetic field on spike growth is through both the suppressed thermal conduction into the unstable spike and the Righi-Leduc heat flow deflecting heat from the spike tip to the base. Righi-Leduc is found to be the dominant effect for small Hall parameters, while suppressed thermal conduction dominates for large Hall parameters. These results demonstrate the importance of considering magnetic fields in all perturbed inertial confinement fusion hot spots.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2019

Real-Time Background Oriented Schlieren: Catching Up With Knife Edge Schlieren

Background Oriented Schlieren (BOS) is a widely used technique that provides density gradient information in flow fields of interest, without imposing stringent optical quality requirements on the facility/experiment windows and/or optics used in the BOS setup. Typically, the BOS reference image is acquired before the test begins (flow off) and then the "live" image data are acquired during the actual testing/experiment (flow on). The raw BOS image data, while displayed in real-time as they are acquired from the camera, unfortunately provide little if any visual indication of the density gradients in the flow. Generally, the "live" images must be processed off-line after the testing is completed, providing no indication of the success of the BOS setup and no feedback on the operational success of the test. Advances in computer processing hardware enables the implementation of real-time processing and display of the BOS image data. Two different approaches to implementing the real-time BOS (RT-BOS) processing capability are described herein. First, a traditional multi-core Central Processing Unit (CPU) based approach using scheduled parallel threads is used to build a RT-BOS processing engine. In the second approach, a Graphical Processing Unit (GPU) approach is used to costruct a RT-BOS processing engine. Generally, high core count CPU processors can provide a useful processing rate for RT-BOS. However, the GPU based approach exceeds the processing capability of the CPU approach, at a fraction of the cost. The GPU approach places no restrictions on the Host PC processing capability, except that it be capable of acquiring the BOS image data from the camera in real-time.

Wernet, Mark P.↗
DOE OSTI2022

Circadian rhythmicity of amyloid‐beta‐related molecules is disrupted in the choroid plexus of a female Alzheimer's disease mouse model

Abstract The choroid plexus (CP) is part of the blood‐cerebrospinal fluid barrier (BCSFB) and was recently described as an important component of the circadian clock system. It is the principal source of cerebrospinal fluid (CSF) and responsible for the synthesis and secretion of various neuroprotective peptides including those involved in amyloid‐β (Aβ) transport/degradation, contributing to Aβ homeostasis. Inadequate Aβ metabolic clearance and transport across the BCSFB have been associated with circadian dysfunctions in Alzheimer's disease (AD) patients. To investigate whether AD pathology influences Aβ scavengers circadian expression, we collected CP at different time points from an AD mouse model (APP/PS1) (female and male animals, aged 6‐ and 12‐months‐old) and analyzed their mRNA expression by Real‐time RT‐PCR. Only angiotensin‐converting enzyme (Ace) expression in 6‐month‐old female wild‐type mice and transthyretin (Ttr) expression in 12‐month‐old female wild‐type mice presented significant rhythmicity. The circadian rhythmicity of Ace and Ttr, prompt us to analyze the involvement of circadian rhythm in Aβ uptake. A human CP papilloma (HIBCPP) cell line was incubated with Aβ‐488 and uptake was evaluated at different time points using flow cytometry. Aβ uptake displayed circadian rhythmicity. Our results suggest that AD might affect Aβ scavengers rhythmicity and that Aβ clearance is a rhythmic process possibly regulated by the rhythmic expression of Aβ scavengers.

Furtado, André↗
DOE OSTI2024

A comprehensive numerical investigation on spray models for Direct-Injection Spark-Ignition engines

Gasoline direct-injection spark-ignition (DISI) engines generate a large portion of their unburned hydrocarbon (UHC) and soot emissions during the cold-start phase. A predictive computational fluid dynamics (CFD) modeling framework can be used to understand the physical processes that characterize fuel spray evolution and fuel-film formation at cold start conditions, which can help to reduce engine-out particulate emissions. This study systematically evaluated spray submodels and developed a set of simulation best practices for physical-numerical submodels with the goal of enabling accurate simulations of liquid spray behavior in a DISI engine. Three comprehensive experimental datasets containing free-spray projected liquid volume (PLV), liquid volume fraction (LVF), and near-field X-ray radiography data were used to validate the simulation results and evaluate the spray submodels. Systematic analysis delved into injected parcel distribution, droplet collision, spray breakup, and evaporation via a detailed assessment of the relevant spray submodels. Moreover, the effects of turbulence models and the initial turbulent flow properties on the liquid spray evolution were examined. Based on extensive calibration efforts, a set of simulation best practices for the free spray was developed and validated against the PLV/LVF data. Simulation results indicated that the uniform distribution for parcel initialization, coupled with appropriate droplet collision submodels, provides an improved spray morphology compared to the cluster distribution. The findings also underscored the importance of calibrating the Kelvin-Helmholtz Rayleigh-Taylor (KH-RT) breakup model constants and droplet heat transfer coefficient scaling factor to achieve favorable agreement regarding measured liquid penetration and spray widths. In conclusion, this study marks a substantial stride towards accurately predicting fuel film evolution and soot formation within DISI engine performance.

ECN Spray G↗
DOE OSTI2022

Deceleration-stage Rayleigh–Taylor growth in a background magnetic field studied in cylindrical and Cartesian geometries

Experiments have identified the Rayleigh–Taylor (RT) instability as one of the greatest obstacles to achieving inertial confinement fusion. Consequently, mitigation strategies to reduce RT growth and fuel–ablator mixing in the hotspot during the deceleration phase of the implosion are of great interest. In this work, the effect of seed magnetic fields on deceleration-phase RT growth are studied in planar and cylindrical geometries under conditions relevant to the National Ignition Facility (NIF) and Omega experiments. The magnetohydrodynamic (MHD) and resistive-MHD capabilities of the FLASH code are used to model imploding cylinders and planar blast-wave-driven targets. Realistic target and laser parameters are presented that suggest the occurrence of morphological differences in late-time RT evolution in the cylindrical NIF case and a measurable difference in spike height of single-mode growth in the planar NIF case. The results of this study indicate the need for target designs to utilize an RT-unstable foam–foam interface in order to achieve sufficient magnetic field amplification to alter RT evolution. Benchmarked FLASH simulations are used to study these magnetic field effects in both resistive and ideal MHD.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1986

Adhesive evaluation of thin films of LARC-TPI and LARC-TPI with 5 mol % ODA

A commercially available LARC-TPI film and an experimentally prepared film of LARC-TPI with 5 mol % of 4,4'-oxydianiline (ODA), designated as LARC-TPI/ODA in the report, supplied by Mitsui Toatsu Chemicals, Incorporated (MTCI), Japan, were evaluated as thermoplastic adhesive films for bonding Ti-6Al-4V. The LARC-TPI/ODA had been shown by MTCI to possess more flow than thermoplastic LARC-TPI and was, therefore, evaluated and compared to the LARC-TPI. Lap shear strength was used to evaluate the materials as adhesives. They were characterized after fracture by determining the glass transition temperature, Tg. The mode of failure was also reported. Thermal exposure at 204C for 500 and 1000 hrs and a 72-hour water-boil were conducted on lap shear specimens prepared with the two adhesive films. Lap shear tests were conducted at RT, 177C, 204C, and 232C before and after exposures.

Progar, D. J.↗