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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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At least 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Numerical simulation of a complete STOVL aifcraft in ground effect

The aerodynamic environment encountered by powered-lift aircraft operating in ground effect is unique among flight vehicles. It is characterized by low forward speed with embedded regions of high subsonic or supersonic jet flows. During ground effect operations, complex recirculating flows generated by the jets produce large changes in the aerodynamic loads on the flight vehicle. Analytic prediction and small-scale experimental methods have produced mixed results in this flight regime, with the result that costly full-scale powered tests are required to evaluate the performance of candidate designs. The ability to accurately predict vehicle performance without resorting to full-scale tests will be critical to future powered-lift aircraft projects. This paper summarizes efforts to predict the flow field about a powered-lift aircraft, the YAV-8B Harrier, in low level jet-borne flight by solution of the Reynolds-averaged Navier-Stokes equations. Results are compared to infrared images of the NASA YAV-8B Harrier V/STOL Systems Research Aircraft (VSRA) under similar flight conditions.

Smith, Merritt H.↗
NASA NTRS1996

Jet Evolution Visualized and Quantified Using Filtered Rayleigh Scattering

Filtered Rayleigh scattering was utilized as a flow diagnostic in an investigation of a method for enhancing mixing in supersonic jets. The primary objectives of the study were to visualize the effect of vortex generating tabs on supersonic jets, to exact quantitative data from these planar visualizations, and to detect the presence of secondary flows (i.e., streamwise vorticity) generated by the tabs. An injection seeded frequency-doubled Nd:YAG was the light source and a 14 bit Princeton Instruments iodine charge coupled display (ICCD) camera recorded the image through an iodine cell. The incident wave length of the laser was held constant for each flow case so that the filter absorbed unwanted background light, but permitted part of the thermally broadened Rayleigh scattering light to pas through. The visualizations were performed for axisymmetric jets (D=1.9 cm) operated at perfectly expanded conditions for Mach 1.0, 1.5, and 2.0. All data were recorded for the jet cross section at x/D=3. One hundred instantaneous images were recorded and averaged for each case, with a threshold set to eliminate unavoidable particulate scattering. A key factor in these experiments was that the stagnation air was heated such that the expansion of the flow in the nozzle resulted in the static temperature in the jet being equal to the ambient temperature, assuming isentropic flow. Since the thermodynamic conditions of the flow were approximately the same for each case, increases in the intensity recorded by the ICCD camera could be directly attributed to the Doppler shift, and hence velocity. Visualizations were performed for Mach 1.5 and Mach 2.0 jets with tabs inserted at the nozzle exit. The distortion of the jet was readily apparent and was consistent with Mie scattering-based visualizations. Asymmetry in the intensities of the images indicate the presence of secondary flow patterns which are consistent with the streamwise vortices measured using more traditional diagnostics in subsonic jets with the same tab configurations. Because each tab causes shocks to form, the assumption of isentropic flow is not valid for these cases. However, within a reasonable first-order estimation,the intensity across the illuminated plane for these cases can be related to a value combining density and velocity.

Reeder, Mark F.↗
NASA NTRS1996

First-Order System Least-Squares for Second-Order Elliptic Problems with Discontinuous Coefficients

The first-order system least-squares methodology represents an alternative to standard mixed finite element methods. Among its advantages is the fact that the finite element spaces approximating the pressure and flux variables are not restricted by the inf-sup condition and that the least-squares functional itself serves as an appropriate error measure. This paper studies the first-order system least-squares approach for scalar second-order elliptic boundary value problems with discontinuous coefficients. Ellipticity of an appropriately scaled least-squares bilinear form of the size of the jumps in the coefficients leading to adequate finite element approximation results. The occurrence of singularities at interface corners and cross-points is discussed. and a weighted least-squares functional is introduced to handle such cases. Numerical experiments are presented for two test problems to illustrate the performance of this approach.

Manteuffel, Thomas A.↗
NASA NTRS1997

Study of Injection of Helium into Supersonic Air Flow Using Rayleigh Scattering

A study of the transverse injection of helium into a Mach 3 crossflow is presented. Filtered Rayleigh scattering is used to measure penetration and helium mole fraction in the mixing region. The method is based on planar molecular Rayleigh scattering using an injection-seeded, frequency-doubled ND:YAG pulsed laser and a cooled CCD camera. The scattered light is filtered with an iodine absorption cell to suppress stray laser light. Preliminary data are presented for helium mole fraction and penetration. Flow visualization images obtained with a shadowgraph and wall static pressure data in the vicinity of the injection are also presented.

Seaholtz, Richard G.↗
NASA NTRS1999

Aeroperformance and Acoustics of the Nozzle with Permeable Shell

Several simple experimental acoustic tests of a spraying system were conducted at the NASA Langley Research Center. These tests have shown appreciable jet noise reduction when an additional cylindrical permeable shell was employed at the nozzle exit. Based on these results, additional acoustic tests were conducted in the anechoic chamber AK-2 at the Central Aerohydrodynamics Institute (TsAGI, Moscow) in Russia. These tests examined the influence of permeable shells on the noise from a supersonic jet exhausting from a round nozzle designed for exit Mach number, M (sub e)=2.0, with conical and Screwdriver-shaped centerbodies. The results show significant acoustic benefits of permeable shell application especially for overexpanded jets by comparison with impermeable shell application. The noise reduction in the overall pressure level was obtained up to approximately 5-8%. Numerical simulations of a jet flow exhausting from a convergent-divergent nozzle designed for exit Mach number, M (sub e)=2.0, with permeable and impermeable shells were conducted at the NASA LaRC and Hampton University. Two numerical codes were used. The first is the NASA LaRC CFL3D code for accurate calculation of jet mean flow parameters on the basis of a full Navier-Stokes solver (NSE). The second is the numerical code based on Tam's method for turbulent mixing noise (TMN) calculation. Numerical and experimental results are in good qualitative agreement.

Gilinsky, M.↗
NASA NTRS1997

Electron-H2 Collisions Studied Using the Finite Element Z-Matrix Method

We have applied the Z-matrix method, using a mixed basis of finite elements and Gaussians, to study e-H2 elastic and inelastic collisions. Special attention is paid to the quality of the basis set and the treatment of electron correlation. The calculated cross sections are invariant, to machine accuracy, with respect to the choice of parameters a, b, d, e as long as they satisfy Equation (3). However, the log derivative approach, i.e., the choice a = -e = 1, b = d = 0 appears to converge slightly faster than other choices. The cross sections agree well with previous theoretical results. Comparison will be made with available experimental data.

Huo, Winifred M.↗
NASA NTRS2009

The Third SeaWiFS HPLC Analysis Round-Robin Experiment (SeaHARRE-3)

Seven international laboratories specializing in the determination of marine pigment concentrations using high performance liquid chromatography (HPLC) were intercompared using in situ samples and a mixed pigment sample. The field samples were collected primarily from oligotrophic waters, although mesotrophic and eutrophic waters were also sampled to create a dynamic range in chlorophyll concentration spanning approximately two orders of magnitude (0.020 1.366 mg m^{-3}) The intercomparisons were used to establish the following: a) the uncertainties in quantitating individual pigments and higher-order variables (sums, ratios, and indices); b) the reduction in uncertainties as a result of applying quality assurance (QA) procedures; c) the importance of establishing a properly defined referencing system in the computation of uncertainties; d) the analytical benefits of performance metrics, and e) the utility of a laboratory mix in understanding method performance. In addition, the remote sensing requirements for the in situ determination of total chlorophyll a were investigated to determine whether or not the average uncertainty for this measurement is being satisfied.

Hooker, Stanford B.↗
NASA NTRS2011

Inverse Design of Low-Boom Supersonic Concepts Using Reversed Equivalent-Area Targets

A promising path for developing a low-boom configuration is a multifidelity approach that (1) starts from a low-fidelity low-boom design, (2) refines the low-fidelity design with computational fluid dynamics (CFD) equivalent-area (Ae) analysis, and (3) improves the design with sonic-boom analysis by using CFD off-body pressure distributions. The focus of this paper is on the third step of this approach, in which the design is improved with sonic-boom analysis through the use of CFD calculations. A new inverse design process for off-body pressure tailoring is formulated and demonstrated with a low-boom supersonic configuration that was developed by using the mixed-fidelity design method with CFD Ae analysis. The new inverse design process uses the reverse propagation of the pressure distribution (dp/p) from a mid-field location to a near-field location, converts the near-field dp/p into an equivalent-area distribution, generates a low-boom target for the reversed equivalent area (Ae,r) of the configuration, and modifies the configuration to minimize the differences between the configuration s Ae,r and the low-boom target. The new inverse design process is used to modify a supersonic demonstrator concept for a cruise Mach number of 1.6 and a cruise weight of 30,000 lb. The modified configuration has a fully shaped ground signature that has a perceived loudness (PLdB) value of 78.5, while the original configuration has a partially shaped aft signature with a PLdB of 82.3.

Li, Wu↗
NASA NTRS2016

Fast Ignition and Sustained Combustion of Ionic Liquids

A catalyst free method of igniting an ionic liquid is provided. The method can include mixing a liquid hypergol with a HAN (Hydroxylammonium nitrate)-based ionic liquid to ignite the HAN-based ionic liquid in the absence of a catalyst. The HAN-based ionic liquid and the liquid hypergol can be injected into a combustion chamber. The HAN-based ionic liquid and the liquid hypergol can impinge upon a stagnation plate positioned at top portion of the combustion chamber.

Joshi, Prakash B.↗
NASA NTRS2018

Compositions and Methods Associated with Intercalating and Exfoliating a Sample

Compositions and methods associated with intercalating and exfoliating a sample are described herein. For example, of a method may include mixing the sample with intercalation materials. The intercalation materials are then intercalated into the sample to obtain a sample intercalated with the intercalation materials. The intercalated sample can then be exfoliated to produce an exfoliated sample.

Hung, Ching-Cheh↗
NASA NTRS2019

Emissions Relationships in Western Forest Fire Plumes: I. Reducing the Effect of Mixing Errors on Emission Factors

Studies of emission factors from biomass burning using aircraft data complement the results of lab studies and extend them to conditions of immense hot conflagrations. We illustrate and discuss emission relationships for 422 individual samples from many forest-fire plumes in the Western US. The samples are from two NASA investigations: ARCTAS (Arctic Research of the Composition of the Troposphere from Aircraft and Satellites) and SEAC4RS (Studies of Emissions and Atmospheric Composition, Clouds, and Climate Coupling by Regional Surveys). This work provides sample-by-sample enhancement ratios (EnRs) for 23 gases and particulate properties. Many EnRs provide candidates for emission ratios (ERs, corresponding to the EnR at the source) when the origin and degree of transformation is understood and appropriate. From these, emission factors (EFs) can be estimated when the fuel dry mass consumed is known or can be estimated using the carbon mass budget approach. This analysis requires understanding the interplay of mixing of the plume with surrounding air. Some initial examples emphasize that measured C(tot) = CO2 + CO in a fire plume does not necessarily describe the emissions of the total carbon liberated in the flames, C(burn). Rather, it represents C(tot) = C(burn) + C(bkgd), which includes possibly varying background concentrations for entrained air. Consequently, we present a simple theoretical description for plume entrainment for multiple tracers from flame to hundreds of kilometers downwind and illustrate some intrinsic linear behaviors. The analysis suggests a Mixed Effects Regression Emission Technique (MERET), which can eliminate occasional strong biases associated with the commonly used normalized excess mixing ratio (NEMR) method. MERET splits C(tot) to reveal C(burn) by exploiting the fact that C(burn) and all tracers respond linearly to dilution, while each tracer has consistent EnR behavior (slope of tracer concentration with respect to C(burn)). The two effects are separable. Two or three or preferably more emission indicators are required as a minimum; here we used ten. Limited variations in the EnRs for each tracer can be incorporated and the variations and co-variations analyzed. The percentage CO yield (or the modified combustion efficiency) plays some role. Other co-relationships involving nitrogen and organic classes are more prominent; these have strong relationships to the C(burn) to O3 emission relationship. In summary, MERET allows fine spatial resolution (EnRs for individual observations) and comparison of similar plumes distant in time and space. Alkene ratios provide us with an approximate photochemical timescale. This allows discrimination and definition, by fire situation, of ERs, allowing us to estimate emission factors.

Chatfield, Robert B.↗
DOE OSTI2020

Probabilistic Forecasting of Generators Startups and Shutdowns in the MISO System Based on Random Forest

Solving security constrained unit commitment (SCUC) problems to plan an economical generation schedule for day-head electricity market has been an important research topic in recent years. Mixed integer programming method (MIP), the-state-of-art approach for solving SCUC problem, is known computationally hard when the number of binary status variables is large. In this paper, a machine learning-based algorithm - random forest (RF), was applied to forecast the startups (SU) and shutdowns (SD) hours of generators, based on historical hourly system condition observations in the Midcontinent Independent System Operator (MISO) system. The main purpose is to reduce the number of binary status variables, by fixing the SU/SD hours to a narrow range of high confidence. This would significantly reduce the size of the decision space, and therefore speed up SCUC solutions with reduced uncertainty.

Lin, Xinming↗
DOE OSTI2022

Plasticized terephthalate-based polyester blends containing fatty acids or esters thereof

A plasticized terephthalate-based polyester blend comprising a terephthalate-based polyester (e.g., polyethylene terephthalate, i.e., PET) homogeneously blended with a fatty acid or ester thereof, wherein said fatty acid or ester thereof is present in said polyester blend in an amount of 1-50 wt %. Also described herein is a method for producing a plasticized terephthalate-based polyester blend, the method comprising melt mixing a terephthalate-based polyester with a fatty acid or ester thereof at a temperature in a range of 230-250° C. to produce said polyester blend, wherein said fatty acid or ester thereof is present in said polyester blend in an amount of 1-50 wt % and is homogeneously blended with said terephthalate-based polyester.

Naskar, Amit K.↗
DOE OSTI2013

Preserving spherical symmetry in axisymmetric coordinates for diffusion problems

Persevering symmetric solutions, even in the under-converged limit, is important to the robustness of production simulation codes. We explore the symmetry preservation in both a continuous nodal and a mixed finite element method. In their standard formulation, neither method preserves spherical solution symmetry in axisymmetric (RZ) coordinates. We propose two methods, one for each family of finite elements, that recover spherical symmetry for low-order finite elements on linear or curvilinear meshes. This is a first step toward understanding achieving symmetry for higher-order elements. (authors)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Direct regeneration of lithium ion cathodes by ionothermal relithiation

A method for relithiating cathode material from spent lithium-based batteries, the method comprising: (i) mixing delithiated cathode material and a lithium salt with an ionic liquid in which the lithium salt is at least partially soluble to form an initial mixture; (ii) heating the initial mixture to a temperature of 100° C. to 300° C. to result in relithiation of the delithiated cathode material; and (iii) separating the ionic liquid from the relithiated cathode material; wherein, in embodiments, the cathode material is a lithium metal oxide, wherein the metal is selected from the group consisting of Ni, Co, Fe, Mn, Al, Zr, Ti, Nb, and combinations thereof, or wherein the cathode material has the formula LiNi x Mn y Co z O 2 , wherein x>0, y>0, z>0, and x+y+z=1; wherein, in some embodiments, the ionic liquid has a nitrogen-containing cationic portion, such as an imidazolium ionic liquid.

Luo, Huimin↗
DOE OSTI2016

Upscaling of Mixed Finite Element Discretization Problems by the Spectral AMGe Method

Here, we propose two multilevel spectral techniques for constructing coarse discretization spaces for saddle-point problems corresponding to PDEs involving a divergence constraint, with a focus on mixed finite element discretizations of scalar self-adjoint second order elliptic equations on general unstructured grids. We use element agglomeration algebraic multigrid (AMGe), which employs coarse elements that can have nonstandard shape since they are agglomerates of fine-grid elements. The coarse basis associated with each agglomerated coarse element is constructed by solving local eigenvalue problems and local mixed finite element problems. This construction leads to stable upscaled coarse spaces and guarantees the inf-sup compatibility of the upscaled discretization. Also, the approximation properties of these upscaled spaces improve by adding more local eigenfunctions to the coarse spaces. The higher accuracy comes at the cost of additional computational effort, as the sparsity of the resulting upscaled coarse discretization (referred to as operator complexity) deteriorates when we introduce additional functions in the coarse space. We also provide an efficient solver for the coarse (upscaled) saddle-point system by employing hybridization, which leads to a symmetric positive definite (s.p.d.) reduced system for the Lagrange multipliers, and to solve the latter s.p.d. system, we use our previously developed spectral AMGe solver. Numerical experiments, in both two and three dimensions, are provided to illustrate the efficiency of the proposed upscaling technique.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS1989

Some issues related to simulation of the tracking and communications computer network

The Communications Performance and Integration branch of the Tracking and Communications Division has an ongoing involvement in the simulation of its flight hardware for Space Station Freedom. Specifically, the communication process between central processor(s) and orbital replaceable units (ORU's) is simulated with varying degrees of fidelity. The results of investigations into three aspects of this simulation effort are given. The most general area involves the use of computer assisted software engineering (CASE) tools for this particular simulation. The second area of interest is simulation methods for systems of mixed hardware and software. The final area investigated is the application of simulation methods to one of the proposed computer network protocols for space station, specifically IEEE 802.4.

Lacovara, Robert C.↗
DOE OSTI2018

Maximum Kolmogorov-Sinai Entropy Versus Minimum Mixing Time in Markov Chains

We establish a link between the maximization of Kolmogorov Sinai entropy (KSE) and the minimization of the mixing time for general Markov chains. Since the maximisation of KSE is analytical and easier to compute in general than mixing time, this link provides a new faster method to approximate the minimum mixing time dynamics. It could be interesting in computer sciences and statistical physics, for computations that use random walks on graphs that can be represented as Markov chains.

97 MATHEMATICS AND COMPUTING↗