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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Sound radiation due to boundary layer transition

This report describes progress made to date towards calculations of noise produced by the laminar-turbulence transition process in a low Mach number boundary layer formed on a rigid wall. The primary objectives of the study are to elucidate the physical mechanisms by which acoustic waves are generated, to clarify the roles of the fluctuating Reynolds stress and the viscous stress in the presence of a solid surface, and to determine the relative efficiency as a noise source of the various transition stages. In particular, we will examine the acoustic characteristics and directivity associated with three-dimensional instability waves, the detached high-shear layer, and turbulent spots following a laminar breakdown. Additionally, attention will be paid to the unsteady surface pressures during the transition, which provide a source of flow noise as well as a forcing function for wall vibration in both aeronautical and marine applications.

Wang, Meng↗
NASA NTRS1994

Quantum propagation in single mode fiber

This paper presents a theory for quantum light propagation in a single-mode fiber which includes the effects of the Kerr nonlinearity, group-velocity dispersion, and linear loss. The theory reproduces the results of classical self-phase modulation, quantum four-wave mixing, and classical solution physics, within their respective regions of validity. It demonstrates the crucial role played by the Kerr-effect material time constant, in limiting the quantum phase shifts caused by the broadband zero-point fluctuations that accompany any quantized input field. Operator moment equations - approximated, numerically, via a terminated cumulant expansion - are used to obtain results for homodyne-measurement noise spectra when dispersion is negligible. More complicated forms of these equations can be used to incorporate dispersion into the noise calculations.

Joneckis, Lance G.↗
NASA NTRS1996

Inlet and Propulsion Integration of Scram Propelled Vehicles

The material to be presented in these two lectures begins with cycle considerations of the turbojet engine combined with a ramjet engine to provide thrust over the range of Mach 0 to 5. We will then examine in some detail the aerodynamic behavior that occurs in the inlet operating near the peak speed. Following that, we shall view a numerical simulation through a baseline scramjet engine, starting at the entrance to the inlet, proceeding into the combustor and through the nozzle. In the next segment, we examine a combined rocket and ramjet propulsion system. Analysis and test results will be examined with a view toward evaluation of the concept as a practical device. Two other inlets will then be reviewed: a Mach 12 inlet and a Mach 18 configuration. Finally, we close our lectures with a discussion of the Detonation Wave engine, and inspect the physical and chemical behavior obtained from numerical simulation. A few final remarks will be made regarding the application of CFD for hypersonic propulsion components.

Povinelli, Louis A.↗
NASA NTRS1977

Chemical Evolution and the Origin of Life: Bibliography 1975

This bibliography is the sixth annual supplement to the comprehensive bibliography on the same subject which was published in Space Life Sci.We would like to draw attention to a recently published cumulative bibliography on this same subject: Biochemical Origin of Life: Chemistry and Life. Soil and Water and Its Relationship to Origin of Life. MR - Studies of Prebiotic Polypeptides. Energy, Matter, and Life. Prospects for the Future Orientation of Scientific Research. Photochemical Formation of Self Sustaining Coacervates. Photochemical Formation of Self-Sustaining Coacervates. Comparative Study of Abiogenesis of Cysteine and Other Amino Acids Catalyzed by Various Metal Ions. Protein Structure and the Molecular Evolution of Biological Energy Conversion. Origin of Life. Clues from Relations Between Chemical Compositions of Living Organisms and Natural Environments. Shock Synthesis of Amino Acids II.', Origins of Life 6(1-2). Dynamics of the Chemical Evolution of Earth's Primitive Atmosphere. The Mechanisms of Amino Acids Synthesis by High Temperature Shock-Waves. Theory of Chemical Evolution. Physical Foundations of Probability of Biogenesis.

West, Martha W.↗
NASA NTRS2004

Transient Three-Dimensional Analysis of Side Load in Liquid Rocket Engine Nozzles

Three-dimensional numerical investigations on the nozzle start-up side load physics were performed. The objective of this study is to identify the three-dimensional side load physics and to compute the associated aerodynamic side load using an anchored computational methodology. The computational methodology is based on an unstructured-grid, and pressure-based computational fluid dynamics formulation, and a simulated inlet condition based on a system calculation. Finite-rate chemistry was used throughout the study so that combustion effect is always included, and the effect of wall cooling on side load physics is studied. The side load physics captured include the afterburning wave, transition from free- shock to restricted-shock separation, and lip Lambda shock oscillation. With the adiabatic nozzle, free-shock separation reappears after the transition from free-shock separation to restricted-shock separation, and the subsequent flow pattern of the simultaneous free-shock and restricted-shock separations creates a very asymmetric Mach disk flow. With the cooled nozzle, the more symmetric restricted-shock separation persisted throughout the start-up transient after the transition, leading to an overall lower side load than that of the adiabatic nozzle. The tepee structures corresponding to the maximum side load were addressed.

Wang, Ten-See↗
NASA NTRS2005

How Special Are Dark Gamma-Ray Burst: A Diagnostic Tool

We present here a comprehensive study of the optical/near-infrared (IR) upper limits for gamma-ray bursts that have an X-ray afterglow. We have extrapolated the X-ray afterglows to optical wavelengths based on the physics of the fireball blast wave model and compared these results with optical upper limits for a large sample of bursts. We find a small set of only three bursts out of a sample of 20 for which the upper limits are not compatible with their X-ray afterglow properties within the context of any blast wave model. This sparse sample does not allow us to conclusively determine the cause of this optical/near-IR deficit. Extinction in the host galaxy is a likely cause, but high redshifts and different afterglow mechanisms might also explain the deficit in some cases. We note that the three bursts appear to have higher than average gamma-my peak fluxes. In a magnitude versus time diagram the bursts are separated from the majority of bursts with a detected optical/near-IR afterglow. However, two gamma- ray bursts with an optical afterglow (one of which is highly reddened) also fall in this region with dark bursts, making it likely that dark bursts are at the faint end of the set of optically detected bursts, and therefore the dark bursts likely form a continuum with the bursts with a detected optical afterglow. Our work provides a useful diagnostic tool for follow-up observations for potentially dark bursts; applied to the events detected with the Swift satellite, it will significantly increase our sample of truly dark bursts and shed light upon their nature. Subject headings: dust, extinction - gamma rays: bursts Online material: machine-readable tables

Rod, Evert↗
NASA NTRS2009

Representations of the Stratospheric Polar Vortices in Versions 1 and 2 of the Goddard Earth Observing System Chemistry-Climate Model (GEOS CCM)

This study will document the behavior of the polar vortices in two versions of the GEOS CCM. Both versions of the model include the same stratospheric chemistry, They differ in the underlying circulation model. Version 1 of the GEOS CCM is based on the Goddard Earth Observing System, Version 4, general circulation model which includes the finite-volume (Lin-Rood) dynamical core and physical parameterizations from Community Climate Model, Version 3. GEOS CCM Version 2 is based on the GEOS-5 GCM that includes a different tropospheric physics package. Baseline simulations of both models, performed at two-degree spatial resolution, show some improvements in Version 2, but also some degradation, In the Antarctic, both models show an over-persistent stratospheric polar vortex with late breakdown, but the year-to-year variations that are overestimated in Version I are more realistic in Version 2. The implications of this for the interactions with tropospheric climate, the Southern Annular Mode, will be discussed. In the Arctic both model versions show a dominant dynamically forced variabi;ity, but Version 2 has a persistent warm bias in the low stratosphere and there are seasonal differences in the simulations. These differences will be quantified in terms of climate change and ozone loss. Impacts of model resolution, using simulations at one-degree and half-degree, and changes in physical parameterizations (especially the gravity wave drag) will be discussed.

Pawson, S.↗
NASA NTRS1984

Remote Sensing of Earth Terrain

Theoretical models that are useful and practical in relating remote sensing data to the important physical parameters characterizing Earth terrain are developed. The development of models that are useful in data analysis and interpretation, scene simulation, and developing new remote sensing approaches and techniques is discussed. Numerous theoretical models that are applicable to the active and passive remote sensing of plowed fields, atmospheric precipitation, vegetation, and snow fields were developed. The radiative transfer theory is used to interpret the active and passive data as a function of rain rate. Both the random medium model and the discrete scatterer model is used to study the remote sensing of vegetation fields. Due to the non-spherical geometry of the scatterers there is strong azimuthal dependence in the observed data. Thus, the anisotropic random medium model and the discrete scatterer model with nonspherical particles was developed. In order to relate the remote sensing data to the actual physical parameters, the scattering of electromagnetic waves from randomly distributed dielectric scatterers was studied. Both the rigorous random discrete scatterer theory and the strong fluctuation theory are used to derive the backscattering cross section in terms of the actual physical parameters and the results agree well with the data obtained from the snow fields.

Kong, J. A.↗
NASA NTRS1976

Shock wave ignition of metal powders

The interaction between isolated metal particles and shock-induced flowfields is analyzed to characterize physical events and determine experimental feasibility for shock wave ignition studies. Emphasis is placed on incident shock wave phenomenon as opposed to reflected shock wave. A pre-ignition particle-flow interaction is hypothesized which presumes a vapor phase ignition reaction and an absence of significant vaporization prior to particle melting and erosion. Rapid vaporization of eroded mass is expected, with ignition reaction in the particle wakes. Experimental observation of the 6438-A Cd line and the 3721-A MgO band support the ignition mechanism hypothesized. Scattered cloud data are believed to substantiate the hypothesis that ignition delays could be correlated with predicted melting times.

Fox, T. W.↗
NASA NTRS1992

ULF waves in the outer magnetosphere of Uranus

ULF waves are ubiquitous in the terrestrial magnetosphere, and play a critical role in the physics of the magnetosphere. A search for similar waves in the Uranian magnetosphere using Voyager 2 magnetometer data reveals ULF waves in the outer magnetosphere near the magnetopause. These waves decrease in amplitude with distance from the magnetopause. In the interior of the magnetosphere the wave level is at or below the noise level of the instrument.

Russell, C. T.↗
NASA NTRS2011

Gravity and Rossby Wave Signatures in the Tropical Troposphere and Lower Stratosphere Based on Southern Hemisphere Additional Ozonesondes (SHADOZ), 1998-2007

Prior investigations attempted to determine the relative influence of advection and convective processes on ozone and water vapor distributions in the tropical tropopause layer (TTL) through analyses of tracers, related physical parameters (e.g., outgoing long-wave radiation, precipitable water, and temperature), or with models. In this study, stable laminae in Southern Hemisphere Additional Ozonesonde Network (SHADOZ) ozone profIles from 1998 to 2007 are interpreted in terms of gravity waves (GW) or Rossby waves (RW) that are identified with vertical and quasi-horizontal displacements, respectively. Using the method of Pierce and Grant (1998) as applied by Thompson et al. (2007a, 2007b, 2010, 2011), amplitudes and frequencies in ozone laminae are compared among representative SHADOZ sites over Africa and the Pacific, Indian, and Atlantic oceans. GW signals maximize in the TTL and lower stratosphere. Depending on site and season, GW are identified in up to 90% of the soundings. GW are most prevalent over the Pacific and eastern Indian oceans, a distribution consistent with vertically propagating equatorial Kelvin waves. Ozone laminae from RW occur more often below the tropical tropopause and with lower frequency 20%). Gravity wave and Rossby wave indices (GWI, RWI) are formulated to facilitate analysis of interannual variability of wave signatures among sites. GWI is positively correlated with a standard ENSO (El Nino-Southern Oscillation) index over American Samoa (14degS, 171degW) and negatively correlated at Watukosek, Java (7.5degS, 114degE), Kuala Lumpur (3degN, 102degE), and Ascension Island (80degS, 15degW). Generally, the responses of GW and RW to ENSO are consistent with prior studies.

Thompson, Anne M.↗
NASA NTRS1986

Plasma wave signatures of collisionless shocks and the role of plasma wave turbulence in shock formation

Observations of the plasma waves associated with collisionless shocks are reviewed, and the understanding of their generation mechanisms and their importance to shock physics are summarized. The emphasis is on waves generated directly at the shock, especially ion acoustic and lower-hybrid-like modes. The observations are discussed in the context of shock structure, with attention given to the distinctions between waves generated in the shock foot and ramp. The behavior of resistive, dispersive, and supercritical quasi-perpendicular shocks is contrasted. Evidence for the operation of various generation mechanisms, including interactions with cross-field currents, gyrating reflected ions, and field-aligned electron beams, are summarized. The various forms of plasma heating which are actually observed are outlined, and the role of the various wave modes in this heating is discussed. Conclusion, it is argued that, while plasma wave turbulence may play a vital role in plasma heating for some special shocks, it is of second-order importance in most cases.

Mellott, M. M.↗
NASA NTRS1980

Plane waves at or near grazing incidence in the parabolic approximation

The parabolic approximation for the acoustic equations of motion is applied to the study of the sound field generated by a plane wave at or near grazing incidence to a finite impedance boundary. It is shown how this approximation accounts for effects neglected in the usual plane wave reflection analysis which, at grazing incidence, erroneously predicts complete cancellation of the incident field by the reflected field. Examples are presented which illustrate that the solution obtained by the parabolic approximation contains several of the physical phenomena known to occur in wave propagation near an absorbing boundary.

Mcaninch, G. L.↗
NASA NTRS1982

July 29, 1977, magnetospheric studies - Impulsive waves, global dynamics and geomagnetic indices

Problems of magnetospheric physics addressed by the Coordinated Data Analysis Workshop are grouped into general areas. Immediate magnetospheric response to changes in the solar wind is considered in studies of impulsive waves traced through the magnetosphere to the ground, and interpreted in terms of fast-mode wave propagation. Magnetopause geometry and microstructure after the arrival of the interplanetary shock were analyzed with data from near-geostationary satellites. A model of particle convection during the first quarter of the day gave important evidence that the convection electric field penetrated to small radial distances for extended intervals, and another model is presented which relates the local time of substorm onset to the sector of the tail that was stressed immediately after the onset of daytime reconnection. The evidence for different reconnection patterns is assessed, and a pattern not previously considered is introduced.

Kivelson, M. G.↗
NASA NTRS2007

A Shock-Refracted Acoustic Wave Model for Screech Amplitude in Supersonic Jets

A physical model is proposed for the estimation of the screech amplitude in underexpanded supersonic jets. The model is based on the hypothesis that the interaction of a plane acoustic wave with stationary shock waves provides amplification of the transmitted acoustic wave upon traversing the shock. Powell's discrete source model for screech incorporating a stationary array of acoustic monopoles is extended to accommodate variable source strength. The proposed model reveals that the acoustic sources are of increasing strength with downstream distance. It is shown that the screech amplitude increases with the fully expanded jet Mach number. Comparisons of predicted screech amplitude with available test data show satisfactory agreement. The effect of variable source strength on the directivity of the fundamental (first harmonic, lowest frequency mode) and the second harmonic (overtone) is found to be unimportant with regard to the principal lobe (main or major lobe) of considerable relative strength, and is appreciable only in the secondary or minor lobes (of relatively weaker strength).

Kandula, Max↗
NASA NTRS2011

Surface Instability of Liquid Propellant under Vertical Oscillatory Forcing

Fluid motion in a fuel tank produced during thrust oscillations can circulate sub-cooled hydrogen near the liquid-vapor interface resulting in increased condensation and ullage pressure collapse. The first objective of this study is to validate the capabilities of a Computational Fluid Dynamics (CFD) tool, CFD-ACE+, in modeling the fundamental interface transition physics occurring at the propellant surface. The second objective is to use the tool to assess the effects of thrust oscillations on surface dynamics. Our technical approach is to first verify the CFD code against known theoretical solutions, and then validate against existing experiments for small scale tanks and a range of transition regimes. A 2D axisymmetric, multi-phase model of gases, liquids, and solids is used to verify that CFD-ACE+ is capable of modeling fluid-structure interaction and system resonance in a typical thrust oscillation environment. Then, the 3D mode is studied with an assumed oscillatory body force to simulate the thrust oscillating effect. The study showed that CFD modeling can capture all of the transition physics from solid body motion to standing surface wave and to droplet ejection from liquid-gas interface. Unlike the analytical solutions established during the 1960 s, CFD modeling is not limited to the small amplitude regime. It can extend solutions to the nonlinear regime to determine the amplitude of surface waves after the onset of instability. The present simulation also demonstrated consistent trends from numerical experiments through variation of physical properties from low viscous fluid to high viscous fluids, and through variation of geometry and input forcing functions. A comparison of surface wave patterns under various forcing frequencies and amplitudes showed good agreement with experimental observations. It is concluded that thrust oscillations can cause droplet formation at the interface, which results in increased surface area and enhanced heat transfer between the liquid and gas phases as the ejected droplets travel well into the warmer gas region.

Yang, H. Q.↗
NASA NTRS1982

A spectral energetics analysis of atmospheric blocking

The spectral energetics of two blocking case studies from the winter of 1978-79 are calculated. One case occurred over the North Atlantic and the other over the North Pacific. The temporal evolution and geographical distribution of the energetics of the planetary-scale (zonal harmonic wavenumbers 1-4) and the intermediate-scale (wavenumbers 5-10) wave ensembles are examined to identify the physical mechanisms important in the blocking process. The Atlantic block was forced by the nonlinear interaction of intense baroclinic cyclone-scale waves with barotropic, ultralong waves. The Pacific blocking resulted from the baroclinic amplification of planetary-scale waves. In addition, at least two necessary conditions are required for the development of blocking. First, one of the forcing mechanisms must be in operation, and second, the phase of the antecedent planetary-scale waves must be such that the forcing mechanism can amplify them into a blocking pattern. In each of the cases studied, the blocking developed downstream of intense intermediate- or large-scale cyclogenesis.

Hansen, A. R.↗