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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

A simulation study of cold electron heating by loss cone instabilities

Results are presented of a computer simulation study of electron cyclotron harmonic waves; an electrostatic finite size particle simulation code is used. The initial electron velocity distribution function is modeled as a hot ring perpendicular to the ambient magnetic field and a cold Maxwellian component. Nonlinear cyclotron resonance is found to be the saturation mechanism of the unstable waves and the heating mechanism of the cold electrons. The results can be related to certain ionospheric phenomena.

Ashour-Abdalla, M.↗
NASA NTRS1980

Coronal heating by stochastic magnetic pumping

Recent observational data cast serious doubt on the widely held view that the Sun's corona is heated by traveling waves (acoustic or magnetohydrodynamic). It is proposed that the energy responsible for heating the corona is derived from the free energy of the coronal magnetic field derived from motion of the 'feet' of magnetic field lines in the photosphere. Stochastic motion of the feet of magnetic field lines leads, on the average, to a linear increase of magnetic free energy with time. This rate of energy input is calculated for a simple model of a single thin flux tube. The model appears to agree well with observational data if the magnetic flux originates in small regions of high magnetic field strength. On combining this energy input with estimates of energy loss by radiation and of energy redistribution by thermal conduction, we obtain scaling laws for density and temperature in terms of length and coronal magnetic field strength.

Sturrock, P. A.↗
NASA NTRS1991

The heating of the solar chromosphere

The solar atmosphere associated with magnetic fields is brighter in characteristic field emitters than the magnetic field-free portion of the atmosphere. The chromosphere can accordingly be identified with the atmosphere within such magnetic elements as flux tubes. Attention is presently given to bright points associated with the intranetwork magnetic fields, which are heated by large-amplitude compressive waves whose periods approximate the 3-min acoustic cutoff period. Relevant line and continuum radiation observations are studied; it is concluded that energy dissipated by the 3-min waves may suffice to heat the low and middle chromosphere, in the bright points, to the temperatures observed.

Kalkofen, Wolfgang↗
NASA NTRS1999

Wave Dynamics and Transport in the Stratosphere

The report discusses: (1) Gravity waves generated by tropical convection: A study in which a two-dimensional cloud-resolving model was used to examine the possible role of gravity waves generated by a simulated tropical squall line in forcing the quasi-biennial oscillation was completed. (2) Gravity wave ray tracing studies:It was developed a linear ray tracing model of gravity wave propagation to extend the nonlinear storm model results into the mesosphere and thermosphere. (3) tracer filamentation: Vertical soundings of stratospheric ozone often exhibit laminated tracer structures characterized by strong vertical tracer gradients. (4) Mesospheric gravity wave modeling studies: Although our emphasis in numerical simulation of gravity waves generated by convection has shifted from simulation of idealized two-dimensional squall lines to the most realistic (and complex) study of wave generation by three-dimensional storms. (5) Gravity wave climatology studies: Mr. Alexander applied a linear gravity wave propagation model together with observations of the background wind and stability fields to compute climatologies of gravity wave activity for comparison to observations. (6) Convective forcing of gravity waves: Theoretical study of gravity wave forcing by convective heat sources has completed. (7) Gravity waves observation from UARS: The objective of this work is to apply ray tracing, and other model technique, in order to determine to what extend the horizontal and vertical variation in satellite observed distribution of small-scale temperature variance can be attributed to gravity waves from particular sources. (8) The annual and interannual variations in temperature and mass flux near the tropical tropopause. and (9) Three dimensional cloud model.

Holton, James R.↗
NASA NTRS1994

Heat-transfer measurements and computations of swept-shock-wave boundary-layer interactions

An experimental and computational research program providing new knowledge of the heat transfer in swept-shock-wave/boundary-layer interactions is described. An equilibrium turbulent boundary layer on a flat plate is subjected to impingement by a swept planar shock wave generated by a sharp fin. Five different interactions with fin angles ranging from 10 to 20 deg at freestream Mach numbers of 3 and 4 produce a variety of interaction strengths ranging from weak to very strong. A foil heater generates a uniform heat flux over the flat plate surface, and miniature thin-film-resistance sensors are used to measure the local surface temperature. The heat convection equation is then solved for the heat transfer distribution within an interaction, yielding an uncertainty of about +/- 10%. These data are compared with numerical Navier-Stokes solutions that employ a k-epsilon turbulence model. A simple peak heat transfer correlation for fin interactions is suggested.

Lee, Y.↗
NASA NTRS1982

The effects of moisture on trapped mountain lee waves

The effects of latent heat release on the dynamics of mountain lee waves are examined with the aid of two-dimensional numerical simulations, for several situations in which the Scorer parameter has a nearly two-layer vertical structure. Changes in the moisture in the lowest layer are found to produce three fundamentally different behaviors: (1) resonant waves in an absolutely stable environment are distorted and untrapped by an increase in moisture; (2) resonant waves in a conditionally unstable layer are destroyed by an increase in moisture; and (3) resonant waves in a moist environment are detuned by a decrease in moisture. Changes in the humidity in the upper layer are found to amplify or damp the wave response, depending on the depth of the lower layer. In most situations, the wave response is significantly more complicated than that predicted by simply replacing the dry stability with an equivalent moist stability in the saturated layer.

Durran, D. R.↗
NASA NTRS1981

Coronal heating by stochastic magnetic pumping

Recent observational data cast serious doubt on the widely held view that the sun's corona is heated by traveling waves (acoustic or magnetohydrodynamic). It is here proposed that the energy responsible for heating the corona is derived from the free energy of the coronal magnetic field derived from motion of the 'feet' of magnetic field lines in the photosphere. Stochastic motion of the feet of magnetic field lines leads, on the average, to a linear increase of magnetic free energy with time. This rate of energy input is calculated for a simple model of a single thin flux tube. The model appears to agree well with observational data if the magnetic flux originates in small regions of high magnetic field strength as proposed by Tarbell et al. (1979). On combining this energy input with estimates of energy loss by radiation and of energy redistribution by thermal conduction, scaling laws are obtained for density and temperature in terms of length and coronal magnetic field strength.

Sturrock, P. A.↗
NASA NTRS1999

Wavenumber Vacillation in Weakly-Stratified Baroclinic Flows

The wavenumber selection in an unstable baroclinic flow has long been a subject of investigation in geophysical fluid dynamics. For a weakly unstable flow, the linearly most unstable wave is always the final realized wave. As the flow becomes more unstable, the dominant wave gradually shifts from the most unstable wave to a longer wave. However, when the supercriticality is reduced from the state with a dominant longwave, it may remain in that state even beyond the threshold where it first developed. Hysteresis in a quasigeostrophic system also displays a complex behavior: it occurs not only between the states of different dominant wavenumbers, but also between the states of identical dominant wavenumber but of different dynamic characteristics. In a recent numerical experiment using a high-resolution spectral Eady model with asymmetric Ekman dissipation, it is found that in a weakly stratified flow with strong meridional forcing the flow does not show a preference for any single wave. Instead, the dominant wave periodically varies among the linearly most unstable wave and the longer waves. The mechanism of wavenumber vacillation will be examined in terms of meridional heat flux, the wave PV gradient, and wave saturation. The importance of wave-wave and wave-mean flow interactions will also be investigated.

Chou, Shih-Hung↗
NASA NTRS1988

Alfven ion-cyclotron heating of ionospheric O(+) ions

Transversely heated ionospheric ions, in particular O(+) ions, are often observed flowing upward along auroral field lines. Currents observed in association with the transversely heated ions can drive shear Alfven waves and electrostatic ion-cyclotron waves unstable which can, in turn, be resonantly absorbed by the ions to produce the heating. Particle simulations are used to examine self-consistently the excitation of these waves and the associated heating. It is shown that the growth of the electrostatic ion-cyclotron waves quickly becomes suppressed as the ions become heated and the dominant wave fields are those of the shear Alfven wave. The resultant transverse ion heating is larger and faster than that produced by solely electrostatic ion-cyclotron wave heating. Due to trapping of ions by the shear Alfven wave, the temperature of the O(+) ions remains comparable to that of the H(+) ions.

Winglee, R. M.↗
NASA NTRS1982

On the preferential acceleration and heating of solar wind heavy ions

The feasibility of producing the observed velocities and temperatures of solar wind heavy ions by the resonant cyclotron interaction with left-polarized hydromagnetic waves was investigated. A "most favorable case" scenario in which the waves are parallel-propagating and dispersionless and the energy for the wave acceleration and heating is taken from saturated low-frequency Alfven waves via a cascade to higher frequencies, is incorporated into a numerical solar wind code and agreement with observation is tested. The resonant cyclotron interaction is shown to fail on at least three points, even in this most favorable case.

Isenberg, P. A.↗
NASA NTRS1987

Heating of the solar corona by the resonant absorption of Alfven waves

An improved method for calculating the resonance absorption heating rate is discussed and the results are compared with observations in the solar corona. To accomplish this, the wave equation for a dissipative, compressible plasma is derived from the linearized magnetohydrodynamic equations for a plasma with transverse Alfven speed gradients. For parameters representative of the solar corona, it is found that a two-scale description of the wave motion is appropriate. The large-scale motion, which can be approximated as nearly ideal, has a scale which is on the order of the width of the loop. The small-scale wave, however, has a transverse scale much smaller than the width of the loop, with a width of about 0.3-250 km, and is highly dissipative. These two wave motions are coupled in a narrow resonance region in the loop where the global wave frequency equals the local Alfven wave frequency. Formally, this coupling comes about from using the method of matched asymptotic expansions to match the inner and outer (small and large scale) solutions. The resultant heating rate can be calculated from either of these solutions. A formula derived using the outer (ideal) solution is presented, and shown to be consistent with observations of heating and line broadening in the solar corona.

Davila, Joseph M.↗
NASA NTRSDate not supplied

Design and Operability of a Variably Premixed Rotating Detonation Engine for the Evaluation of Mixing Effects

The design of a variably premixed rotating detonation engine (RDE) is presented with preliminary experimental results. Premixed operation decouples the mixing process from the detonation cycle, enabling direct comparison with premixed simulations. A porous medium, formed into a ring of 6.45 mm radial thickness, serves as the premixture injector, arresting potential flash-back events. Two chamber geometries are tested, the first aimed at eliminating recirculation zones and comprised of a 7.62 mm wide channel, the width of which the porous injector occupies 85%. The second chamber geometry features a 10.7 mm channel width and a 3.08 mm wide backward-facing step on the internal diameter of the premixture injector. Transverse optical access is incorporated into the design using a transparent outer body. Tests were conducted at mixing conditions ranging from non-premixed to fully premixed with gaseous hydrogen and air reactants in the narrow-channel configuration. Engine operating modes and detonation wave speeds were characterized using aft-end high-speed chemiluminescence imaging, while detonation wave topology and heat release in the refill zone are captured by transverse imaging. A two-wave counterpropagating mode was most commonly observed in the narrow-channel configuration with wave speeds ranging from 49-67% of the theoretical Chapman-Jouguet (CJ) velocity. Fully premixed operation in the backward-facing step configuration rendered wave speeds up to 86% of CJ velocity, consistent with previous non-premixed results using the same channel width and a backward-facing step. These results demonstrate successful premixed RDE operation with high wave speeds and highlight the role of product recirculation zones in stabilizing the detonation cycle.

detonation↗
NASA NTRS1993

Coronal heating by the resonant absorption of Alfven waves - Importance of the global mode and scaling laws

Numerical simulations of the MHD equations for a fully compressible, low-beta, resistive plasma are used to study the resonance absorption process for the heating of coronal active region loops. Comparisons with more approximate analytic models show that the major predictions of the analytic theories are, to a large extent, confirmed by the numerical computations. The simulations demonstrate that the dissipation occurs primarily in a thin resonance layer. Some of the analytically predicted features verified by the simulations are (a) the position of the resonance layer within the initial inhomogeneity; (b) the importance of the global mode for a large range of loop densities; (c) the dependence of the resonance layer thickness and the steady-state heating rate on the dissipation coefficient; and (d) the time required for the resonance layer to form. In contrast with some previous analytic and simulation results, the time for the loop to reach a steady state is found to be the phase-mixing time rather than a dissipation time. This disagreement is shown to result from neglect of the existence of the global mode in some of the earlier analyses. The resonant absorption process is also shown to behave similar to a classical driven harmonic oscillator.

Steinolfson, Richard S.↗
NASA NTRS1993

Gravity wave forcing in the middle atmosphere due to reduced ozone heating during a solar eclipse

We present an analysis of the gravity wave structure and the associated forcing of the middle atmosphere induced by the screening of the ozone layer from solar heating during a solar eclipse. Fourier integral techniques and numerical evaluation of the integral solutions were used to assess the wave field structure and to compute the gravity wave forcing of the atmosphere at greater heights. Our solutions reveal dominant periods of a few hours, characteristic horizontal and vertical scales of about 5000 to 10,000 km and 200 km, respectively, and an integrated momentum flux in the direction of eclipse motion of about 5.6 x 10 exp 8 N at each height above the forcing level. These results suggest that responses to solar eclipses may be difficult to detect above background gravity wave and tidal fluctuations until well into the thermosphere. Conversely, the induced body forces may penetrate to considerable heights because of the large wave scales and will have significant effects at levels where the wave field is dissipated.

Fritts, David C.↗
NASA NTRS1977

Heating of the lower thermosphere by the dissipation of acoustic waves

Infrasound of 0.2 Hz known as microbaroms, generated by interfering ocean waves, propagates into the lower thermosphere where it is dissipated between 110 and 140 km. It is shown here that under average conditions in winter the energy input into this region is of the order of 0.33 W/kg, the same as that estimated for gravity wave dissipation, and capable of producing a heating of at least 30 K/day. To arrive at this result different dissipation mechanisms are discussed, with the calculated attenuation compared to previously published observations and observations of natural infrasound at Palisades, N.Y. Increased acoustic attenuation due to the presence of turbulence is not, in general, in evidence.

Rind, D.↗
NASA NTRS1988

Numerical simulations of an oblique detonation wave engine

An account is given of the numerical methods employed in a code for the simulation of supersonic combustion, which is then applied to the simulation of attached detonations and flames associated with the oblique-detonation wave supersonic combustor concept. The addition of heat by a detonation wave results in a shorter combustor than can be obtained in more conventional scramjet designs. Pure oblique detonations have been produced in a stoichiometric, uniformly mixed hydrogen/air stream; the wave rotates upstream with energy release, according to simple analytical arguments. Flow visualization maps for Mach number and temperature are presented.

Cambier, Jean-Luc↗