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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

The Transient Dendritic Solidification Experiment (TDSE)

Dendritic solidification is a common mode of solidification. It is also an important model problem in nonequilibrium physics and pattern formation physics. Current theories couple the transfer of latent heat with selection mechanisms at the interface. Measurements of succinonitrile (SCN) dendrites in microgravity show reasonable agreement between heat transfer predictions and experiment. However, data and analysis for assessing interfacial physics theories are less definitive. We are studying, and will present data on, transient effects in dendritic growth of SCN. We employ the Clapeyron pressure/melting temperature effect to make a rapid change in a sample's hydrostatic pressure, and thereby rapidly change the specimen's melting temperature, forcing the dendrite to select a new steady-state. These initial measurements show some surprising and non-intuitive effects.

Koss, M. B.↗
NASA NTRS2016

A Physics-Based Approach to Hypersonic Nonequilibrium Chemistry

NASA has undertaken a concerted effort to generate a complete model for the chemical reactions and other collisional processes that take place in the bow shock layer and wake of spacecraft entering the atmospheres of Earth and Mars. This new model is based on first-principles physics calculations: interaction potentials between colliding species obtained from accurate quantum mechanics calculations and reaction rate coefficients and cross sections based on classical mechanics simulations of heavy particle collisions.This presentation will give an introduction to the underlying theory and computational methods used in this work and describe the range of chemical and physical processes that take place in the close vicinity of spacecraft during atmospheric entry. I will also present some of our recent results for reactions involving nitrogen, carbon monoxide and CO2.

Jaffe, Richard↗
NASA NTRS1982

The effect of physical aging on the time-dependent properties of carbon-fiber-reinforced epoxy composites

Annealing in nitrogen below the glass transition temperature T(g) is found to affect the matrix-dominated physical properties of postcured, (+ and -45)2s specimens of Thornel 300 carbon fiber/Fiberite 934 epoxy composite as well as neat Fiberite 934 epoxy resin. The damping behavior, stress-relaxation rate and enthalpic state of the matrix material are found to decrease as functions of annealing time. The time-dependent change in physical properties is explained on the basis of free-volume collapse related to the physical aging of the nonequilibrium glassy network of epoxy. Such physical aging in network epoxy has been demonstrated to be thermoreversible through the monitoring of its kinetics by differential scanning calorimetry, stress relaxation tests, and dynamic mechanical analysis.

Kong, E. S. W.↗
NASA NTRS1989

Conservation equations and physical models for hypersonic air flows in thermal and chemical nonequilibrium

The conservation equations for simulating hypersonic flows in thermal and chemical nonequilibrium and details of the associated physical models are presented. These details include the curve fits used for defining thermodynamic properties of the 11 species air model, curve fits for collision cross sections, expressions for transport properties, the chemical kinetics models, and the vibrational and electronic energy relaxation models. The expressions are formulated in the context of either a two or three temperature model. Greater emphasis is placed on the two temperature model in which it is assumed that the translational and rotational energy models are in equilibrium at the translational temperature, T, and the vibrational, electronic, and electron translational energy modes are in equilibrium at the vibrational temperature, T sub v. The eigenvalues and eigenvectors associated with the Jacobian of the flux vector are also presented in order to accommodate the upwind based numerical solutions of the complete equation set.

Peter A. Gnoffo↗
NASA NTRS1987

Transient ionization and solar flare X-ray spectra

In this paper the effects of a transiently ionizing solar flare plasma on the X-ray spectrum of iron between 1.85 and 1.92 A are considered. The atomic physics of the nonequilibrium spectrum is discussed, and reasons for differences in appearance from ionization equilibrium spectra are explained. The effect of spectral resolution on the ability to detect transient ionization in the iron X-ray spectrum is illustrated by synthetic spectra. A synthetic transiently ionizing spectrum is applied to the interpretation of spectra obtained from the SOX 1 spectrometer on the Japanese Hinotori spacecraft. Some indications of transient ionization are found, although counting statistics negate a strong conclusion. A hypothetical spectrometer with about one order of magnitude more sensitivity than the SOX 1 Hinotori or the bent crystal spectrometer flown on the Solar Maximum Mission (SMM) is also considered. The ranges of plasma parameters such as plasma emission measure and density that are necessary for transient ionization to be detected by such an instrument are discussed.

Doschek, G. A.↗
NASA NTRS1994

Aerothermodynamic methods for a Mars environmental survey Mars entry

Computational fluid dynamics models for the thermodynamics and transport properties used in an equilibrium version of the Langley aerothermodynamics upwind relaxation algorithm (LAURA) for Mars atmospheric entries are described. In addition, the physical models used in a nonequilibrium version of LAURA for Mars-entry flows are described. Uncertainties exist in defining constants used in the transport properties for the equilibrium model and in many of the physical models for the nonequilibrium version. Solutions from the two codes using the best available constants are examined at the Mars-entry conditions characteristics of the Mars environmental survey mission. While the flowfields are near thermal equilibrium, chemical nonequilibrium effects are present in the entry cases examined. Convective heating at the stagnation point for these flows (assuming fully catalytic wall boundary conditions) is approximately 100 W/cm(exp 2). Radiative heating is negligible.

AEROTHERMODYNAMIC METHODS↗
NASA NTRS1993

Aerothermodynamics of a MESUR Martian entry

Computational fluid dynamics models for the thermodynamics and transport properties used in an equilibrium version of the Langley Aerothermodynamics Upwind Relaxation Algorithm (LAURA) for Martian Atmospheric entries are described. In addition, the physical models used in a nonequilibrium version of LAURA for Martian-entry flows are described. Uncertainties exist in defining constants used in the transport properties for the equilibrium model and in many of the physical models for the nonequilibrium version. Solutions from the two codes using the best available constants are examined at the Martian-entry conditions characteristic of the Mars Environmental Survey (MESUR) mission. While the flowfields are near thermal equilibrium, chemical nonequilibrium effects are present in the entry cases examined. Convective heating at the stagnation point for these flows (assuming fully catalytic wall boundary conditions) is approximately 100 W/sq cm. Radiative heating is negligible.

Mitcheltree, R. A.↗
NASA NTRS1978

Influence of precursor heating on viscous flow around a Jovian entry body

The influence of changes in precursor region flow properties (resulting from the absorption of radiation from the shock layer) on the entire shock layer flow phenomena is investigated. Axially symmetric case is considered for both the preheating zone (precursor region) and shock layer. The flow in the shock layer is considered to be viscous with chemical equilibrium but radiative nonequilibrium. Realistic thermo-physical and spectral models are employed and results are obtained by implicit finite difference and iterative procedures. The results indicate that precursor heating increases the radiative heating of the body by a maximum of 7.5% for a 116 KM entry conditions.

Tiwari, S. N.↗
NASA NTRS1981

Physical aging in graphite epoxy composites

The matrix dominated mechanical behavior of a graphite epoxy composite was found to be affected by sub Tg annealing. Postcured + or - 45 deg 4S specimens of Thornel 300 graphite/Narmco 5208 epoxy were quenched from above Tg and given a sub Tg annealing at 140 C for times up to 10 to the 5th power min. The ultimate tensile strength, strain to break, and toughness of the composite material were found to decrease as functions of sub Tg annealing time. No weight loss was observed during the sub Tg annealing. The time dependent change in mechanical behavior is explained on the basis of free volume changes that are related to the physical aging of the nonequilibrium glassy network epoxy. The results imply possible changes in composite properties with service time.

Kong, E. S. W.↗
NASA NTRS1985

A review of shock waves around aeroassisted orbital transfer vehicles

Aeroassisted orbital transfer vehicles (AOTVs) are a proposed type of reusable spacecraft that would be used to transport cargoes from one Earth-bound orbit to another. Such vehicles could be based on the proposed space station and used to transport commercial satellites from the space station to geostationary orbits or to polar orbits and return. During a mission, AOTVs would fly through Earth's atmosphere, thus generating aerodynamic forces that could be used for decelerating the vehicles or changing their direction. AOTV research findings were concerned with the shock-wave-induced, high-temperature airflows that would be produced around these vehicles during atmospheric flight. Special emphasis was placed on the problems of: (1) the chemical physics of multitemperature, ionizing, nonequilibrium air flows, and (2) the dynamics of the flows in the base region of a blunt body with complex afterbody geometry.

Park, C.↗
NASA NTRS1986

A review of shock waves around aeroassisted orbital transfer vehicles

Aeroassisted orbital transfer vehicles (AOTVs) are a proposed type of reusable spacecraft that would be used to transport cargoes from one earth-bound orbit to another. Such vehicles could be based on the proposed space station and used to transport commercial satellites from the space station to geostationary orbits or to polar orbits and return. During a mission, AOTVs would fly through earth's atmosphere, thus generating aerodynamic forces that could be used for decelerating the vehicles or changing their direction. AOTV research findings were concerned with the shock-wave-induced, high-temperature airflows that would be produced around these vehicles during atmospheric flight. Special emphasis was placed on the problems of: (1) the chemical physics of multitemperature, ionizing, nonequilibrium air flows, and (2) the dynamics of the flows in the base region of a blunt body with complex afterbody geometry.

Park, C.↗
NASA NTRS2012

Modeling, Measurements, and Fundamental Database Development for Nonequilibrium Hypersonic Aerothermodynamics

The design of entry vehicles requires predictions of aerothermal environment during the hypersonic phase of their flight trajectories. These predictions are made using computational fluid dynamics (CFD) codes that often rely on physics and chemistry models of nonequilibrium processes. The primary processes of interest are gas phase chemistry, internal energy relaxation, electronic excitation, nonequilibrium emission and absorption of radiation, and gas-surface interaction leading to surface recession and catalytic recombination. NASAs Hypersonics Project is advancing the state-of-the-art in modeling of nonequilibrium phenomena by making detailed spectroscopic measurements in shock tube and arcjets, using ab-initio quantum mechanical techniques develop fundamental chemistry and spectroscopic databases, making fundamental measurements of finite-rate gas surface interactions, implementing of detailed mechanisms in the state-of-the-art CFD codes, The development of new models is based on validation with relevant experiments. We will present the latest developments and a roadmap for the technical areas mentioned above

Bose, Deepak↗
NASA NTRS1983

Physical aging in graphite/epoxy composites

Sub-Tg annealing has been found to affect the properties of graphite/epoxy composites. The network epoxy studied was based on the chemistry of tetraglycidyl 4,4'-diamino-diphenyl methane (TGDDM) crosslinked by 4,4'-diamino-diphenyl sulfone (DDS). Differential scanning calorimetry, thermal mechanical analysis, and solid-state cross-polarized magic-angle-spinning nuclear magnetic resonance spectroscopy have been utilized in order to characterize this process of recovery towards thermodynamic equilibrium. The volume and enthalpy recovery as well as the 'thermoreversibility' aspects of the physical aging are discussed. This nonequilibrium and time-dependent behavior of network epoxies are considered in view of the increasingly wide applications of TGDDM-DDS epoxies as matrix materials of structural composites in the aerospace industry.

Kong, E. S. W.↗
NASA NTRS1993

Molecular gas dynamics applied to low-thrust propulsion

The Direct Simulation Monte Carlo method is currently being applied to study flowfields of small thrusters, including both the internal nozzle and the external plume flow. The DSMC method is employed because of its inherent ability to capture nonequilibrium effects and proper boundary physics in low-density flow that are not readily obtained by continuum methods. Accurate prediction of both the internal and external nozzle flow is important in determining plume expansion which, in turn, bears directly on impingement and contamination effects.

Zelesnik, Donna↗
NASA NTRS2011

Model-Based Diagnostics for Propellant Loading Systems

The loading of spacecraft propellants is a complex, risky operation. Therefore, diagnostic solutions are necessary to quickly identify when a fault occurs, so that recovery actions can be taken or an abort procedure can be initiated. Model-based diagnosis solutions, established using an in-depth analysis and understanding of the underlying physical processes, offer the advanced capability to quickly detect and isolate faults, identify their severity, and predict their effects on system performance. We develop a physics-based model of a cryogenic propellant loading system, which describes the complex dynamics of liquid hydrogen filling from a storage tank to an external vehicle tank, as well as the influence of different faults on this process. The model takes into account the main physical processes such as highly nonequilibrium condensation and evaporation of the hydrogen vapor, pressurization, and also the dynamics of liquid hydrogen and vapor flows inside the system in the presence of helium gas. Since the model incorporates multiple faults in the system, it provides a suitable framework for model-based diagnostics and prognostics algorithms. Using this model, we analyze the effects of faults on the system, derive symbolic fault signatures for the purposes of fault isolation, and perform fault identification using a particle filter approach. We demonstrate the detection, isolation, and identification of a number of faults using simulation-based experiments.

Daigle, Matthew John↗
NASA NTRS1983

Influence of physical aging on the time-dependent properties of network epoxies and epoxy-matrix composites

The matrix-dominated properties of a network epoxy and its carbon fiber-reinforced composite are noted to be affected by sub-glass transition temperature T(g) annealing in a nitrogen atmosphere. The damping behavior, stress relaxation rate, and enthalpic state of the matrix material were found to decrease as functions of sub-T(g) annealing time. This time-dependent change in physical properties is explained on the basis of a free-volume collapse which is related to the recovery process of the nonequilibrium glassy network of the epoxy. The physical aging in network epoxies has been demonstrated to be thermoreversible. Aging kinetics are studied by means of differential scanning calorimetry, stress relaxation tests, dynamic mechanical analysis, and thermomechanical analysis.

Kong, E. S. W.↗