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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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All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

Impact of Variations on 1-D Flow in Gas Turbine Engines via Monte Carlo Simulations

The unsteady compressible inviscid flow is characterized by the conservations of mass, momentum, and energy; or simply the Euler equations. In this paper, a study of the subsonic one-dimensional Euler equations with local preconditioning is presented using a modal analysis approach. Specifically, this study investigates the behavior of airflow in a gas turbine engine using the specified conditions at the inflow and outflow boundaries of the compressor, combustion chamber, and turbine, to determine the impact of variations in pressure, velocity, temperature, and density at low Mach numbers. Two main questions motivate this research: 1) Is there any aerodynamic problem with the existing gas turbine engines that could impact aircraft performance? 2) If yes, what aspect of a gas turbine engine could be improved via design to alleviate that impact and to optimize aircraft performance? This paper presents an initial attempt to model the flow behavior in terms of their eigenfrequencies subject to the assumption of the uncertainty or variation (perturbation). The flow behavior is explored using simulation outputs from a customer-deck model obtained from Pratt & Whitney. Variations of the main variables (i.e., pressure, temperature, velocity, density) about their mean states at the inflow and outflow boundaries of the compressor, combustion chamber, and turbine are modeled. Flow behavior is analyzed for the high-pressure compressor and combustion chamber utilizing the conditions on their left and right boundaries. In the same fashion, similar analyses are carried out for the high-pressure and low-pressure turbines. In each case, the eigenfrequencies that are obtained for different boundary conditions are examined closely based on their probabilistic distributions, a result of a Monte Carlo 10,000 sample simulation. Furthermore, the characteristic waves and wave response are analyzed and contrasted among different cases, with and without preconditioners. The results reveal the existence of flow instabilities due to the combined effect of variations and excessive pressures in the case of the combustion chamber and high-pressure turbine. Finally, a discussion is presented on potential impacts of the instabilities and what can be improved via design to alleviate them for a better aircraft performance.

Ngo, Khiem Viet↗
NASA NTRS2007

Space Weather Nowcasting of Atmospheric Ionizing Radiation for Aviation Safety

There is a growing concern for the health and safety of commercial aircrew and passengers due to their exposure to ionizing radiation with high linear energy transfer (LET), particularly at high latitudes. The International Commission of Radiobiological Protection (ICRP), the EPA, and the FAA consider the crews of commercial aircraft as radiation workers. During solar energetic particle (SEP) events, radiation exposure can exceed annual limits, and the number of serious health effects is expected to be quite high if precautions are not taken. There is a need for a capability to monitor the real-time, global background radiations levels, from galactic cosmic rays (GCR), at commercial airline altitudes and to provide analytical input for airline operations decisions for altering flight paths and altitudes for the mitigation and reduction of radiation exposure levels during a SEP event. The Nowcast of Atmospheric Ionizing Radiation for Aviation Safety (NAIRAS) model is new initiative to provide a global, real-time radiation dosimetry package for archiving and assessing the biologically harmful radiation exposure levels at commercial airline altitudes. The NAIRAS model brings to bear the best available suite of Sun-Earth observations and models for simulating the atmospheric ionizing radiation environment. Observations are utilized from ground (neutron monitors), from the atmosphere (the METO analysis), and from space (NASA/ACE and NOAA/GOES). Atmospheric observations provide the overhead shielding information and the ground- and space-based observations provide boundary conditions on the GCR and SEP energy flux distributions for transport and dosimetry simulations. Dose rates are calculated using the parametric AIR (Atmospheric Ionizing Radiation) model and the physics-based HZETRN (High Charge and Energy Transport) code. Empirical models of the near-Earth radiation environment (GCR/SEP energy flux distributions and geomagnetic cut-off rigidity) are benchmarked against the physics-based CMIT (Coupled Magnetosphere- Ionosphere-Thermosphere) and SEP-trajectory models.

Mertens, Christopher J.↗
NASA NTRS2012

Calculating Soil Wetness, Evapotranspiration and Carbon Cycle Processes Over Large Grid Areas Using a New Scaling Technique

Soil wetness typically shows great spatial variability over the length scales of general circulation model (GCM) grid areas (approx 100 km ), and the functions relating evapotranspiration and photosynthetic rate to local-scale (approx 1 m) soil wetness are highly non-linear. Soil respiration is also highly dependent on very small-scale variations in soil wetness. We therefore expect significant inaccuracies whenever we insert a single grid area-average soil wetness value into a function to calculate any of these rates for the grid area. For the particular case of evapotranspiration., this method - use of a grid-averaged soil wetness value - can also provoke severe oscillations in the evapotranspiration rate and soil wetness under some conditions. A method is presented whereby the probability distribution timction(pdf) for soil wetness within a grid area is represented by binning. and numerical integration of the binned pdf is performed to provide a spatially-integrated wetness stress term for the whole grid area, which then permits calculation of grid area fluxes in a single operation. The method is very accurate when 10 or more bins are used, can deal realistically with spatially variable precipitation, conserves moisture exactly and allows for precise modification of the soil wetness pdf after every time step. The method could also be applied to other ecological problems where small-scale processes must be area-integrated, or upscaled, to estimate fluxes over large areas, for example in treatments of the terrestrial carbon budget or trace gas generation.

Sellers, Piers↗
NASA NTRS2006

Granular Contact Forces: Proof of "Self-Ergodicity" by Generalizing Boltzmann's Stosszahlansatz and H Theorem

Ergodicity is proved for granular contact forces. To obtain this proof from first principles, this paper generalizes Boltzmann's stosszahlansatz (molecular chaos) so that it maintains the necessary correlations and symmetries of granular packing ensembles. Then it formally counts granular contact force states and thereby defines the proper analog of Boltzmann's H functional. This functional is used to prove that (essentially) all static granular packings must exist at maximum entropy with respect to their contact forces. Therefore, the propagation of granular contact forces through a packing is a truly ergodic process in the Boltzmannian sense, or better, it is self-ergodic. Self-ergodicity refers to the non-dynamic, internal relationships that exist between the layer-by-layer and column-by-column subspaces contained within the phase space locus of any particular granular packing microstate. The generalized H Theorem also produces a recursion equation that may be solved numerically to obtain the density of single particle states and hence the distribution of granular contact forces corresponding to the condition of self-ergodicity. The predictions of the theory are overwhelmingly validated by comparison to empirical data from discrete element modeling.

Metzger, Philip T.↗
NASA NTRS2015

Evaluation of Case Size 0603 BME Ceramic Capacitors

High volumetric efficiency of commercial base metal electrode (BME) ceramic capacitors allows for a substantial reduction of weight and sizes of the parts compared to currently used military grade precious metal electrode (PME) capacitors. Insertion of BME capacitors in space applications requires a thorough analysis of their performance and reliability. In this work, six types of cases size 0603 BME capacitors from three vendors have been evaluated. Three types of multilayer ceramic capacitors (MLCCs) were designed for automotive industry and three types for general purposes. Leakage currents in the capacitors have been measured in a wide range of voltages and temperatures, and measurements of breakdown voltages (VBR) have been used to assess the proportion and severity of defects in the parts. The effect of soldering-related thermal shock stresses was evaluated by analysis of distributions of VBR for parts in 'as is' condition and after terminal solder dip testing at 350 C. Highly Accelerated Life Testing (HALT) at different temperatures was used to assess the activation energy of degradation of leakage currents and predict behavior of the parts at life test and normal operating conditions. To address issues related to rework and manual soldering, capacitors were soldered onto different substrates at different soldering conditions. The results show that contrary to a common assumption that large-size capacitors are mostly vulnerable to soldering stresses, cracking in small size capacitors does happen unless special measures are taken during assembly processes.

testing↗
NASA NTRS2011

High Precision Thermal, Structural and Optical Analysis of an External Occulter Using a Common Model and the General Purpose Multi-Physics Analysis Tool Cielo

The efficient simulation of multidisciplinary thermo-opto-mechanical effects in precision deployable systems has for years been limited by numerical toolsets that do not necessarily share the same finite element basis, level of mesh discretization, data formats, or compute platforms. Cielo, a general purpose integrated modeling tool funded by the Jet Propulsion Laboratory and the Exoplanet Exploration Program, addresses shortcomings in the current state of the art via features that enable the use of a single, common model for thermal, structural and optical aberration analysis, producing results of greater accuracy, without the need for results interpolation or mapping. This paper will highlight some of these advances, and will demonstrate them within the context of detailed external occulter analyses, focusing on in-plane deformations of the petal edges for both steady-state and transient conditions, with subsequent optical performance metrics including intensity distributions at the pupil and image plane.

integrated modeling↗
NASA NTRS2017

Assessment of lnternational Space Station (ISS) Lithium-ion Battery Thermal Runaway (TR)

This task was developed in the wake of the Boeing 787 Dreamliner lithium-ion battery TR incidents of January 2013 and January 2014. The Electrical Power Technical Discipline Team supported the Dreamliner investigations and has followed up by applying lessons learned to conduct an introspective evaluation of NASA's risk of similar incidents in its own lithium-ion battery deployments. This activity has demonstrated that historically NASA, like Boeing and others in the aerospace industry, has emphasized the prevention of TR in a single cell within the battery (e.g., cell screening) but has not considered TR severity-reducing measures in the event of a single-cell TR event. center dotIn the recent update of the battery safety standard (JSC 20793) to address this paradigm shift, the NASA community included requirements for assessing TR severity and identifying simple, low-cost severity reduction measures. This task will serve as a pathfinder for meeting those requirements and will specifically look at a number of different lithium-ion batteries currently in the design pipeline within the ISS Program batteries that, should they fail in a Dreamliner-like incident, could result in catastrophic consequences. This test is an abuse test to understand the heat transfer properties of the cell and ORU in thermal runaway, with radiant barriers in place in a flight like test in on orbit conditions. This includes studying the heat flow and distribution in the ORU. This data will be used to validate the thermal runaway analysis. This test does not cover the ambient pressure case. center dotThere is no pass/ fail criteria for this test.

Graika, Jason↗
NASA NTRS2018

Greedy Sampling and Incremental Surrogate Model-Based Tailoring of Aeroservoelastic Model Database for Flexible Aircraft

This paper presents a data analysis and modeling framework to tailor and develop linear parameter-varying (LPV) aeroservoelastic (ASE) model database for flexible aircrafts in broad 2D flight parameter space. The Kriging surrogate model is constructed using ASE models at a fraction of grid points within the original model database, and then the ASE model at any flight condition can be obtained simply through surrogate model interpolation. The greedy sampling algorithm is developed to select the next sample point that carries the worst relative error between the surrogate model prediction and the benchmark model in the frequency domain among all input-output channels. The process is iterated to incrementally improve surrogate model accuracy till a pre-determined tolerance or iteration budget is met. The methodology is applied to the ASE model database of a flexible aircraft currently being tested at NASA/AFRC for flutter suppression and gust load alleviation. Our studies indicate that the proposed method can reduce the number of models in the original database by 67%. Even so the ASE models obtained through Kriging interpolation match the model in the original database constructed directly from the physics-based tool with the worst relative error far below 1%. The interpolated ASE model exhibits continuously-varying gains along a set of prescribed flight conditions. More importantly, the selected grid points are distributed non-uniformly in the parameter space, a) capturing the distinctly different dynamic behavior and its dependence on flight parameters, and b) reiterating the need and utility for adaptive space sampling techniques for ASE model database compaction. The present framework is directly extendible to high-dimensional flight parameter space, and can be used to guide the ASE model development, model order reduction, robust control synthesis and novel vehicle design of flexible aircraft.

numerical analysi↗
NASA NTRS2018

Vegetation Change Detection in Southern California Solar Energy Developments

Change detection from satellite sensor vegetation indices (VIs) presents an opportunity to monitor trends and disturbances at the regional scale for southern California's Mojave and Lower Colorado Deserts. Renewable energy sites are being constructed in this region on public lands under the Bureau of Land Management (BLM). We have developed a framework for VI change detection over the past two decades, with initial focus on three sites, Joshua Tree National Park, Mojave National Preserve, and a proximal group of Development Focus Areas (DFAs), for comparison between protected and development-targeted lands. Three Terra MODIS VIs (normalized difference [NDVI], enhanced [EVI], soil-adjusted [SAVI]) were evaluated in the Breaks for Additive Season and Trend (BFAST) setting for the regional MODIS 250-m resolution grid to estimate significant time series shifts (breakpoints) from February 2000 to May 2018. All three VIs tended to detect the maximum number of breakpoints at a grid location, but cross-correlations with precipitation and comparison with timing of wildfire burns near the study sites for breakpoint density (proportion of area with a breakpoint) showed that NDVI had the strongest response to these major disturbances, supporting its use for subsequent analysis. Time series of NDVI breakpoint change densities for individual solar energy sites did not have a consistent vegetation response following construction. Bootstrapping showed that the DFAs had significantly larger kurtosis and variance in the positive NDVI breakpoint distribution than did the protected sites, but there was no significant difference in the negative distribution for all three sites. The inconsistent post-construction NDVI signal and the large number of breakpoints overall suggested that the largest changes in vegetation cover density were tied to seasonal precipitation amounts. The distributional results indicated that existing site-specific conditions were the main control on VI responses, given the history of human disturbances in the DFAs. Although the results do not support persistent VI disturbances resulting from recent solar energy development, continued monitoring and examination of other ecological variables and surface temperatures will be vital to the long-term protection of this desert environment.

Potter, Christopher S.↗
NASA NTRS2020

Advanced Modular Power System Fully Populated Electronics Enclosure Thermal Testing

A thermal test of an enclosure housing the AMPS electronics cards was performed. The enclosure was fully populated with 17 nonfunctioning AMPS electronics cards. Heaters were applied to the cards to simulate their operation. A cold plate was installed on the top of the case. The case was then insulated to simulate its installation within an electronics rack with the face and rear of the enclosure left open. The cold plate was connected to a chiller which provided cooling water at a fixed input temperature to the cold plate. Flow rates from the chiller of 0.0 L/min, 1.4 L/min and 1.8 L/min were tested. The test was operated at each flow rate over a range of heater power levels until the steady state temperature of the electronics cards was reached. Heater power levels from 2.5 W/card to 45 W/card were tested. The data collected was used to determine the steady state operating temperature of the cards, the temperature distribution between the cards, the time to reach steady-state temperature, the change in steady state temperature with change in heater power, the temperature distribution between the cards at the steady state condition and the heat lost to the surrounds by the enclosure. One of the main goals of the testing was to determine how much waste heat the cards could generate and still maintain a touch temperature at or below 40°C. Based on this requirement, for the 3 cooling rates tested, the maximum card waste heat that could be generated by each individual card was 3.9 W, 16.3 W and 17.6 W respectively. An analysis was also set up to provide an analytical model to estimate the card temperature under different cold plate flow rates and card heater power levels. The results off the analysis was compared to that of the experiment of the range of flow rates and power levels tested.

Anthony Colozza↗
NASA NTRS2022

Microstructure Segmentation with Deep Learning Encoders Pre-Trained on a Large Microscopy Dataset

This study examined the improvement of microscopy segmentation accuracy by transfer learning from a large dataset of microscopy images called MicroNet. Many neural network encoder architectures, including VGG, Inception, and ResNet, were trained on over 100,000 labelled microscopy images from 54 classes. These pre-trained encoders were then embedded into multiple segmentation architectures including U-Net and DeepLabV3+ to evaluate segmentation performance on newly created benchmark microscopy datasets. Compared to ImageNet pre-training, models pre-trained on MicroNet generalized better to out-of-distribution micrographs taken under different imaging and sample conditions and were more accurate with less training data. When training with only a single Ni-superalloy image, pre-training on MicroNet produced a 72.2 percent reduction in relative segmentation error. These results suggest that transfer learning from large in-domain datasets generate models with learned feature representations that are more useful for downstream tasks and will likely improve any microscopy image analysis technique that can leverage pre-trained encoders.

machine learning↗
NASA NTRS2022

Microstructure Segmentation With Deep Learning Encoders Pre-Trained on a Large Microscopy Dataset

This study examined the improvement of microscopy segmentation intersection over union accuracy by transfer learning from a large dataset of microscopy images called MicroNet. Many neural network encoder architectures were trained on over 100,000 labeled microscopy images from 54 material classes. These pre-trained encoders were then embedded into multiple segmentation architectures including UNet and DeepLabV3+ to evaluate segmentation performance on created benchmark microscopy datasets. Compared to ImageNet pre-training, models pre-trained on MicroNet generalized better to out-of-distribution micrographs taken under different imaging and sample conditions and were more accurate with less training data. When training with only a single Ni-superalloy image, pre-training on MicroNet produced a 72.2% reduction in relative intersection over union error. These results suggest that transfer learning from large in-domain datasets generate models with learned feature representations that are more useful for downstream tasks and will likely improve any microscopy image analysis technique that can leverage pre-trained encoders.

machine learning↗
NASA NTRS2022

Impact of Future Low-Emissions Combustor Technology on Acoustic Scaling Laws

A first-of-its-kind examination of broadband noise associated with a far-term advanced low-emission aero-combustor concept is presented. Due to design trends and expected cycle changes for future aircraft propulsion systems, noise generated by sources in the combustor are expected to become of increasing significance for airport-community noise. The paper assesses the impact on legacy semi-empirical noise-prediction methods from the expected radical departures from current combustor operating conditions and designs, such as fuel-air distribution and flame anchoring techniques. Such methods are essential in system-level noise assessments at the preliminary design stage for advanced air transports to assure that overall environmental goals are met. Detailed unsteady pressure measurements, obtained in a fundamental combustion noise experiment utilizing a combustor rig at relevant pressures and temperatures, are analyzed. In addition to an advanced far-term low-emissions concept, a reference configuration with the test section arranged to model a modern combustor sector was also studied. For the test rig in the current-generation configuration, the measured broadband acoustic data are reasonably well described by the acoustic-power scaling laws used in legacy semi-empirical noise-prediction methods. For the future-advanced configuration, the legacy scaling laws, with some notable exceptions, provide correct trends, but with much less accuracy

aeroacoustics↗
NASA NTRS1989

On the generation of a bubbly universe - A quantitative assessment of the CfA slice

A first attempt is made to calculate the properties of the matter distribution in a universe filled with overlapping bubbles produced by multiple explosions. Each spherical shell follows the cosmological Sedov-Taylor solution until it encounters another shell. Thereafter, mergers are allowed to occur in pairs on the basis of N-body results. At the final epoch, the matrix of overlapping shells is populated with 'galaxies' and the properties of slices through the numerically constructed cube compare well with CfA survey results for specified initial conditions. A statistic is found which measures the distance distribution from uniformly distributed points to the nearest galaxies on the projected plane which appears to provide a good measure of the bubbly character of the galaxy distribution. In a quantitative analysis of the CfA 'slice of the universe', a very good match is found between simulation and the real data for final average bubble radii of (13.5 + or - 1.5)/h Mpc with formal filling factor 1.0-1.5 or actual filling factor of 65-80 percent.

Ostriker, J. P.↗
NASA NTRS1951

Investigation of Turbine-outlet Temperature Distribution of XJ34-WE-32 Turbojet Engine

Turbine-outlet radial temperature distributions of an XJ34-WE-32 turbojet engine were investigated in the altitude wind tunnel at the NACA Lewis laboratory over a range of pressure altitudes, engine-inlet air temperatures and flight Mach numbers at or near rated engine conditions. From blade stress considerations, the turbine-outlet temperature distribution was considered satisfactory at altitudes up to 25,000 feet at corrected engine speeds corresponding to rated speed (12,500 rpm); however, operation at either higher corrected engine speeds or higher altitudes resulted in an inversion of the turbine temperature distribution that was detrimental to turbine life. Installation of a compressor-outlet mixer greatly improved the turbine radial temperature distribution.

Prince, W R↗
NASA NTRS1989

A method for solution of the Euler-Bernoulli beam equation in flexible-link robotic systems

An efficient numerical method for solving the partial differential equation (PDE) governing the flexible manipulator control dynamics is presented. A finite-dimensional model of the equation is obtained through discretization in both time and space coordinates by using finite-difference approximations to the PDE. An expert program written in the Macsyma symbolic language is utilized in order to embed the boundary conditions into the program, accounting for a mass carried at the tip of the manipulator. The advantages of the proposed algorithm are many, including the ability to (1) include any distributed actuation term in the partial differential equation, (2) provide distributed sensing of the beam displacement, (3) easily modify the boundary conditions through an expert program, and (4) modify the structure for running under a multiprocessor environment.

Tzes, Anthony P.↗
NASA NTRS1927

Calculating thrust distribution and efficiency of air propellers

I am now proposing a method for the preliminary approximate calculation of the thrust distribution and efficiency of air propellers under any operating conditions. Our task becomes the following, namely, to determine the speed relations and the forces developed on a section with a given direction and velocity of the air current, a problem which can be solved with the aid of the momentum theory.

PROPELLERS - DESIGN & THEORY↗
NASA NTRS2010

HIFiRE Direct-Connect Rig (HDCR) Phase I Ground Test Results from the NASA Langley Arc-Heated Scramjet Test Facility

The initial phase of hydrocarbon-fueled ground tests supporting Flight 2 of the Hypersonic International Flight Research Experiment (HIFiRE) Program has been conducted in the NASA Langley Arc-Heated Scramjet Test Facility (AHSTF). The HIFiRE Program, an Air Force-lead international cooperative program includes eight different flight test experiments designed to target specific challenges of hypersonic flight. The second of the eight planned flight experiments is a hydrocarbon-fueled scramjet flight test intended to demonstrate dual-mode to scramjet-mode operation and verify the scramjet performance prediction and design tools. A performance goal is the achievement of a combusted fuel equivalence ratio greater than 0.7 while in scramjet mode. The ground test rig, designated the HIFiRE Direct Connect Rig (HDCR), is a full-scale, heat sink, direct-connect ground test article that duplicates both the flowpath lines and the instrumentation layout of the isolator and combustor portion of the flight test hardware. The primary objectives of the HDCR Phase I tests are to verify the operability of the HIFiRE isolator/combustor across the Mach 6.0-8.0 flight regime and to establish a fuel distribution schedule to ensure a successful mode transition prior to the HiFIRE payload Critical Design Review. Although the phase I test plans include testing over the Mach 6 to 8 flight simulation range, only Mach 6 testing will be reported in this paper. Experimental results presented here include flowpath surface pressure, temperature, and heat flux distributions that demonstrate the operation of the flowpath over a small range of test conditions around the nominal Mach 6 simulation, as well as a range of fuel equivalence ratios and fuel injection distributions. Both ethylene and a mixture of ethylene and methane (planned for flight) were tested. Maximum back pressure and flameholding limits, as well as a baseline fuel schedule, that covers the Mach 5.84-6.5 test space have been identified.

Hass, Neal E.↗