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NASA NTRS1986

Polar warming in the middle atmosphere of Mars

During the 1984 Mars opposition, ground-based laser heterodyne spectroscopy was obtained for the nonthermal core emission of the 10.33-micron R(8) and 10.72-micron P(32) lines of C-12(O-16)2 at 23 locations on the Martian disk. It is deduced on the basis of these data that the temperature of the middle Martian atmosphere varies with latitude, and a meridional gradient of 0.4-0.9 K/deg latitude is indicated. The highest temperatures are noted to lie at high latitudes in the winter hemisphere; as in the terrestrial case of seasonal effects at the menopause, this winter polar warming in the Martian middle atmosphere requires departures from radiative equilibrium. Two-dimensional circulation model comparisons with these results indicate that atmospheric dust may enhance this dynamical heating at high winter latitudes.

Deming, D.↗

NASA NTRS1986

Bifurcations in unsteady aerodynamics

Nonlinear algebraic functional expansions are used to create a form for the unsteady aerodynamic response that is consistent with solutions of the time dependent Navier-Stokes equations. An enumeration of means of invalidating Frechet differentiability of the aerodynamic response, one of which is aerodynamic bifurcation, is proposed as a way of classifying steady and unsteady aerodynamic phenomena that are important in flight dynamics applications. Accomodating bifurcation phenomena involving time dependent equilibrium states within a mathematical model of the aerodynamic response raises an issue of memory effects that becomes more important with each successive bifurcation.

Tobak, M.↗

NASA NTRS1987

Bifurcations in unsteady aerodynamics

Nonlinear algebraic functional expansions are used to create a form for the unsteady aerodynamic response that is consistent with solutions of the time dependent Navier-Stokes equations. An enumeration of means of invalidating Frechet differentiability of the aerodynamic response, one of which is aerodynamic bifurcation, is proposed as a way of classifying steady and unsteady aerodynamic phenomena that are important in flight dynamics applications. Accommodating bifurcation phenomena involving time dependent equilibrium states within a mathematical model of the aerodynamic response raises an issue of memory effects that becomes more important with each successive bifurcation.

Tobak, M.↗

NASA NTRS1988

The turbulent interstellar medium and pressure-bounded molecular clouds

The existence of turbulence throughout the interstellar medium suggests that an appropriate value for the average pressure may be P/K larger than about 10,000. Negative-index polytropic models of interstellar clouds in equilibrium with an external medium at these pressures are predicted to have sizes, line widths, masses, and size-line width and size-density relations in good agreement with those observed and inferred for dark clouds. Thus these observed features of interstellar clouds do not require that they be completely self-gravitating or 'virialized' in the commonly used sense.

Maloney, Philip↗

NASA NTRS1989

Experimental and computational results for 5 degree blunt cones with shock generators at high velocity

Experiments and computations have been performed under laminar conditions in air on 5-deg blunt cones at velocities of 5 km/s and 6 km/s and at Reynolds numbers of 100,000 and 1 million. The computations were performed using ideal-, equilibrium- and nonequilibrium-chemistry models for air. At the conditions of the tests, the aerodynamic coefficients are sensitive to the real-gas effects present, and both experimental and computational aerodynamic coefficients show real-gas and nonlinear effects. The nonequilibrium computations show that a large amount of oxygen is dissociated in the blunt nose region of the flow and much of the oxygen remains dissociated over the entire length of the body, providing an insight into the source of the observed effects in the aerodynamic coefficients. The experimental and computational shock-shapes are in good agreement.

Strawa, A. W.↗

NASA NTRS1990

Upwind techniques for flows with multiple translational temperatures

The numerical simulation of high-speed flows out of chemical and thermodynamic equilibrium is considered. A general model for the species internal energy is utilized, which allows for multiple translational temperatures. A study of the characteristic wave speeds for the case of two translational temperatures, one associated with the average thermal speed of the heavy particles and the other associated with the translational temperature of free electrons, yields some very interesting results, with acoustic wave speeds of the symmetric form u + or - a no longer appearing. An asymptotic analysis in terms of small electron mass fractions yields approximate wave speed which recover the symmetric form, with the addition of a new wave speed associated with the electron energy equation.

Cinnella, Pasquale↗

NASA NTRS1991

Computer code for single-point thermodynamic analysis of hydrogen/oxygen expander-cycle rocket engines

This analysis and this computer code apply to full, split, and dual expander cycles. Heat regeneration from the turbine exhaust to the pump exhaust is allowed. The combustion process is modeled as one of chemical equilibrium in an infinite-area or a finite-area combustor. Gas composition in the nozzle may be either equilibrium or frozen during expansion. This report, which serves as a users guide for the computer code, describes the system, the analysis methodology, and the program input and output. Sample calculations are included to show effects of key variables such as nozzle area ratio and oxidizer-to-fuel mass ratio.

Glassman, Arthur J.↗

NASA NTRS1993

Deriving Indicial Response From Navier-Stokes Equations

Report discusses research directed toward recasting indicial-response approach into form appropriate to study of vortex-induced oscillations and related aerodynamic and aeroelastic phenomena. Serves two purposes: to show how deficiencies of prior mathematical model overcome to include effects of memory necessary for modeling of oscillatory but otherwise equilibrium state; and using method developed to analyze particular case of flow past cylinder in periodic forced transverse motion.

Truong, K. V.↗

NASA NTRS1994

Extension of the BRYNTRN code to monoenergetic light ion beams

A monoenergetic version of the BRYNTRN transport code is extended to beam transport of light ions (H-2, H-3, He-3, and He-4) in shielding materials (thick targets). The redistribution of energy in nuclear reactions is included in transport solutions that use nuclear fragmentation models. We also consider an equilibrium target-fragment spectrum for nuclei with mass number greater than four to include target fragmentation effects in the linear energy transfer (LET) spectrum. Illustrative results for water and aluminum shielding, including energy and LET spectra, are discussed for high-energy beams of H-2 and He-4.

Cucinotta, Francis A.↗

NASA NTRS1994

Non-local thermodynamic equilibrium limb radiance from O3 and CO2 in the 9-11 micrometer spectral region

Satellite remote sensing of mesospheric and thermospheric O3 abundance in the terrestrial atmosphere often uses 9-11 micrometer thermal emission. In this paper, we apply a line-by-line non-local thermodynamic equilibrium (non-LTE) radiance model to this spectral region and investigate the conditions of LTE breakdown and the effect that this has on the limb radiance measured by an i.r. sounder. Monochromatic and band-integrated radiance calculations have been performed for limb view tangent heights between 55 and 105 km under daytime and nighttime conditions. Non-LTE emission from both O3 and CO2 are shown to be important with the divergence of radiance from LTE values and the diurnal variation being band dependent. We have shown that the contribution of the CO2 bands to the Limb Infrared Monitor of the Stratosphere O3 channel is significant for daytime conditions at tangent heights above about 60 km. A study has been made to choose O3 sounding channel spectral passbands for the High Resolution Dynamics Limb Sounder. High resolution calculations are required to determine those spectral intervals that will filter radiance from selected bands and characterize their non-LTE behavior. This will allow for improved O3 retrievals above 70 km and non-LTE studies.

Edwards, David P.↗

NASA NTRS1995

Stellar oxygen abundances. 4: Systematic effects on oxygen abundances derived from the 6300 A (O I) and 7774 A O I lines

We consider potential systematic effects on oxygen abundances derived from the 6300 A (OI) line and the 7774 A OI triplet. Our solar intensity spectra of the 7774 A triplet confirm previous results which indicate a discrepancy between the observed equivalent widths of Altrock (1968) and the values predicted by Local Thermodynamic Equilibrium (LTE) and recent NLTE models. However, this disagreement (at low micron(s)) does not seem to affect the solar O abundance as derived from flux spectra. We derive O abundances for a selection of relatively metal-rich F and G dwarfs from both the 6300 A (OI) line and 7774 A OI triplet and detail the various uncertainties which enter into the analyses. Minimizing possible systematic effects to the extent possible, we find for T(sub eff) approximately less than 6200-6300 K no systematic difference between the 6300 and 7774 A abundances. For T(sub eff) approximately greater than 6200-6300 K, however 7774 A abundances are substantially larger than the 6300 A abundances. This agreement in O abundances from the two features at cooler T(sub eff) conflicts with that of others and we suggest that the discrepancy may be due to the different model atmospheres utilized. If recently proposed, hotter T(sub eff) values for metal-poor dwarfs are correct, then there appears to be no discrepancy between the 6300 A abundances of metal-poor giants are correct, then there appears to be no discrepancy between the 6300 A abundances of metal-poor giants or dwarfs and the 7774 A abundances for dwarfs. This would seem to rule out substantial LTE departures or atmospheric inhomogeneity effects skewing metal-poor O abundances from the 7774 A triplet (for cooler stars having low metallicity anyway). Given the repeated inability of authors to reproduce each others' O abundances from the 6300 A (OI) line and the uncertainties in the solar equivalent width, we question the usual assumption that the 6300 A (OI) line and the uncertainties in the solar equivalent width, we question the usual assumption that the 6300 A (OI) abundances are more reliable than those from the permitted triplet.

King, Jeremy R.↗

NASA NTRS1999

Properties of QBO and SAO Generated by Gravity Waves

We present an extension for the 2D (zonal mean) version of our Numerical Spectral Mode (NSM) that incorporates Hines' Doppler spread parameterization (DSP) for small scale gravity waves (GW). This model is applied to describe the seasonal variations and the semi-annual and quasi-biennial oscillations (SAO and QBO). Our earlier model reproduced the salient features of the mean zonal circulation in the middle atmosphere, including the QBO extension into the upper mesosphere inferred from UARS measurements. In the present model we incorporate also tropospheric heating to reproduce the upwelling at equatorial latitudes associated with the Brewer-Dobson circulation that affects significantly the dynamics of the stratosphere as Dunkerton had pointed out. Upward vertical winds increase the period of the QBO observed from the ground. To compensate for that, one needs to increase the eddy diffusivity and the GW momentum flux, bringing the latter closer to values recommended in the DSP. The QBO period in the model is 30 months (mo), which is conducive to synchronize this oscillation with the seasonal cycle of solar forcing. Multi-year interannual oscillations are generated through wave filtering by the solar driven annual oscillation in the zonal circulation. Quadratic non-linearities generate interseasonal variations to produce a complicated pattern of variability associated with the QBO. The computed temperature amplitudes for the SAO and QBO are in substantial agreement with observations at equatorial and extratropical latitudes. At high latitudes, however, the observed QBO amplitudes are significantly larger, which may be a signature of propagating planetary waves not included in the present model. The assumption of hydrostatic equilibrium not being imposed, we find that the effects from the vertical Coriolis force associated with the equatorial oscillations are large for the vertical winds and significant for the temperature variations even outside the tropics but are relatively small for the zonal winds.

Mayr, H. G.↗

NASA NTRS1996

On the Growth of Ternary System HNO3/H2SO4/H2O Aerosol Particles in the Stratosphere

We present a study of the growth of ternary solution (nitric acid, sulfuric acid and water) droplets in the stratosphere. The growth mechanism is hetero-molecular condensation in which the particle is assumed to be in equilibrium with environmental water vapor. Model results are in reasonable agreement with the averaged extinction ratio obtained by the SAM II satellite system.

Hamill, Patrick↗

NASA NTRS2002

Prebiotic Processing induced by Comet and Meteor Impact

In their study of organic synthesis from impact shocks using the laser-induced-plasma (LIP) technique, McKay and Borucki(l) found that organic synthesis preferentially occurred in a reducing gas mixture rich in methane, and not in a mixture rich in carbon dioxide. This result means chemical models based on the thermodynamical equilibrium approach do not apply to shock chemistry. In this study, we employ the technique of reacting flow, i.e., chemical kinetics in a fluid flow, to simulate the chemistry occurring in LIP and in the wake region from comet or meteor impact. Three different air compositions have been used: (1) 1/3 CO2 and 2/3 H2, (2) pure CH4, and (3) 1/4 CH4, 1/4 CO2, and 1/2 H2O. The stoichiometric ratio of gas mixtures (1) and (3) are kept the same. For (1) we obtain equal mole fractions of CO and H2O as the major products and for (2) C2H2 is the major product. In both cases our results are in agreement with Ref. (1). For (3) we find an interesting case where the nature of chemicals produced to be critically dependent on the flowfield temperature. At the higher temperature part of the wake region, CO and H2O are the dominant products, whereas in the cooler region C2H2 is the dominant product. Further studies of these reactions, as well as for the gas mixture including N2, are being pursued.

Dateo, Christopher E.↗

NASA NTRS2003

A XMM-Newton Observation of Nova LMC 1995, a Bright Supersoft X-ray Source

Nova LMC 1995, previously detected during 1995-1998 with ROSAT, was observed again as a luminous supersoft X-ray source with XMM-Newton in December of 2000. This nova offers the possibility to observe the spectrum of a hot white dwarf, burning hydrogen in a shell and not obscured by a wind or by nebular emission like in other supersoft X-ray sources. Notwithstanding uncertainties in the calibration of the EPIC instruments at energy E<0.5 keV, using atmospheric models in Non Local Thermonuclear Equilibrium we derived an effective temperature in the range 400,000-450,000 K, a bolometric luminosity Lbolabout equal to 2.3 times 10 sup37 erg s sup-l, and we verified that the abundance of carbon is not significantly enhanced in the X-rays emitting shell. The RGS grating spectra do not show emission lines (originated in a nebula or a wind) observed for some other supersoft X-ray sources. The crowded atmospheric absorption lines of the white dwarf cannot be not resolved. There is no hard component (expected from a wind, a surrounding nebula or an accretion disk), with no counts above the background at E>0.6 keV, and an upper limit Fx,hard = 10 sup-14 erg s sup-l cm sup-2 to the X-ray flux above this energy. The background corrected count rate measured by the EPIC instruments was variable on time scales of minutes and hours, but without the flares or sudden obscuration observed for other novae. The power spectrum shows a peak at 5.25 hours, possibly due to a modulation with the orbital period. We also briefly discuss the scenarios in which this nova may become a type Ia supernova progenitor.

Orio, Marina↗

NASA NTRS2003

SPARC-IGAC Symposium on Climate-Chemistry Interactions. Climate Feedback by Water Vapor in the Tropical Upper Troposphere

The strong greenhouse forcing by atmospheric water vapor is expected to play an important role in shaping the direction of any future changes in climate. We present calculations that provide a new perspective on the sensitivity of upper tropospheric water vapor to changes in surface temperature. Equilibrium states of our atmospheric model show unambiguously that as the surface warms, changes in the vertical distribution and temperature of detraining air parcels from tropical convection lead to higher water vapor mixing ratios in the upper troposphere. However, the increase in mixing ratio is not as large as the increase in saturation mixing ratio due to warmer environmental temperatures, so that the relative humidity decreases. Our analysis suggests that models that maintain a fixed relative humidity are likely overestimating the magnitude of the water vapor feedback.

Dessler, A. E.↗

NASA NTRS1995

Simultaneous concentration and purification through gradient deformation chromatography

Mobile-phase additives, commonly used to modulate absorbate retention in gradient elution chromatography, are usually assumed to be either linearly retained or unretained. Previous theoretical work from our laboratory has shown that these modulators, such as salts in ion-exchange and hydrophobic interaction chromatography and organic modifiers in reversed-phase chromatography, can absorb nonlinearly, giving rise to gradient deformation. Consequently, adsorbate peaks that elute in the vicinity of the head of the deformed gradient may exhibit unusual shapes, form shoulders, and/or be concentrated. These effects for a reversed-phase sorbent with aqueous acetonitrile (ACN) as the modulator are verified experimentally. Gradient deformation is demonstrated experimentally and agrees with simulations based on ACN isotherm parameters that are independently determined from batch equilibrium studies using the layer model. Unusual absorbate peak shapes were found experimentally for single-component injections of phenylalanine, similar to those calculated by the simulations. A binary mixture of tryptophan and phenylalanine is used to demonstrate simultaneous concentration and separation, again in agreement with simulations. The possibility of gradient deformation in ion-exchange and hydrophobic interaction chromatography is discussed.

NASA Discipline Number 93-10↗

NASA NTRS2014

One Dimensional Analysis Model of a Condensing Spray Chamber Including Rocket Exhaust Using SINDA/FLUINT and CEA

Modeling droplet condensation via CFD codes can be very tedious, time consuming, and inaccurate. CFD codes may be tedious and time consuming in terms of using Lagrangian particle tracking approaches or particle sizing bins. Also since many codes ignore conduction through the droplet and or the degradating effect of heat and mass transfer if noncondensible species are present, the solutions may be inaccurate. The modeling of a condensing spray chamber where the significant size of the water droplets and the time and distance these droplets take to fall, can make the effect of droplet conduction a physical factor that needs to be considered in the model. Furthermore the presence of even a relatively small amount of noncondensible has been shown to reduce the amount of condensation. It is desirable then to create a modeling tool that addresses these issues. The path taken to create such a tool is illustrated. The application of this tool and subsequent results are based on the spray chamber in the Spacecraft Propulsion Research Facility (B2) located at NASA's Plum Brook Station that tested an RL-10 engine. The platform upon which the condensation physics is modeled is SINDAFLUINT. The use of SINDAFLUINT enables the ability to model various aspects of the entire testing facility, including the rocket exhaust duct flow and heat transfer to the exhaust duct wall. The ejector pumping system of the spray chamber is also easily implemented via SINDAFLUINT. The goal is to create a transient one dimensional flow and heat transfer model beginning at the rocket, continuing through the condensing spray chamber, and finally ending with the ejector pumping system. However the model of the condensing spray chamber may be run independently of the rocket and ejector systems detail, with only appropriate mass flow boundary conditions placed at the entrance and exit of the condensing spray chamber model. The model of the condensing spray chamber takes into account droplet conduction as well as the degrading effect of mass and heat transfer due to the presence of noncondensibles. The one dimension model of the condensing spray chamber makes no presupposition on the pressure profile within the chamber, allowing the implemented droplet physics of heat and mass transfer coupled to the SINDAFLUINT solver to determine a transient pressure profile of the condensing spray chamber. Model results compare well to the RL-10 engine pressure test data.

Chemical Equilibrium↗