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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 235 records · Page 13
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NASA NTRS1987

A simulation of the IPS variations from a magnetohydrodynamical simulation

Calculations of the variations of interplanetary scintillation (IPS) from a disturbance simulated by a 3-D magnetohydrodynamical (MHD) model of the solar wind are presented. The simulated maps are compared with observations and it is found that the MHD model reproduces the qualitative features of observed disturbances. The disturbance produced by the MHD simulation is found to correspond in strength with the weakest disturbance which can be reliably detected by existing single station IPS observations.

Tappin, S. J.↗
NASA NTRS1985

The solar/interplanetary/magnetosphere/ionosphere connection - A strategy for prediction of geomagnetic storms

A physically-based strategy for the prediction of geomagnetic/ionospheric disturbances, the Solar-Terrestrial/Environmental Model (STEM 2000), is proposed, with application to the prediction of periods of spacecraft charging. Synoptic solar observations provide input for MHD models for flare occurrence, propagation of coronal disturbances, and high speed solar wind streams. A three-dimensional interplanetary MHD model determines solar wind parameters including the energy flux and the cross-magnetosphere tail electric field. Observational earth data are used to predict local time, high latitude ionospheric disturbances which have an impact on the ionospheric structure.

Dryer, M.↗
NASA NTRS1985

The solar-flare induced earth's environment

A composite numerical simulation model developed from a series of MHD models was used to compute the solar-flare-generated disturbances of physical parameters, such as density, temperature, velocity, and magnetic field from the solar surface (i.e., the photospheric level) to the earth's environment. It is shown that the disturbed earth's environment at high latitudes can be approximated by starting with the knowledge of the occurrence and the strength of a solar flare, then simulating the evolutionary consequences of the solar disturbance through interplanetary space up to and through the magnetosphere.

Wu, S. T.↗
NASA NTRS1987

Sooting and disruption in spherically symmetrical combustion of decane droplets in air

The paper presents the results of experiments on the burning of individual 1-2 mm decane droplets in air at room temperature and atmospheric pressure. The NASA Lewis 2.2 s drop tower was used as well as a newly designed droplet-combustion apparatus that promotes nearly spherically symmetrical combustion. Unanticipated disruptions related to sooting behavior were encountered.

Dryer, F. L.↗
NASA NTRS1988

A Three-Dimensional, Time-Dependent Numerical Modeling of Super-Sonic, Super-Alfvenic MHD Flow

A three-dimensional, time-dependent, MHD disturbance propagating through a steady inhomogeneous MHD flow is analyzed by a numerical model based on the Lax-Wendroff finite difference method. The initial steady MHD flow is assumed to be supersonic and super-Alfvenic. The background steady MHD flow is obtained by dropping the time-dependent terms in the unsteady MHD equations. A transient MHD disturbance corresponding to a MHD shock is generated at the lower radial boundary surface. The resulting development and propagation of 3-D MHD disturbances interacting with the background steady MHD flow are numerically simulated in this first application to the field of interplanetary physics. Detailed descriptions of the mathematical formulation and numerical methodology are presented. Example computations are performed to demonstrate the validity of the formulation and the capabilities of the model.

Han, S. M.↗
NASA NTRS1988

The role of magnetohydrodynamics in heliospheric space plasma physics research

Magnetohydrodynamics (MHD) is a fairly recent extension of the field of fluid mechanics. While much remains to be done, it has successfully been applied to the contemporary field of heliospheric space plasma research to evaluate the 'macroscopic picture' of some vital topics via the use of conducting fluid equations and numerical modeling and simulations. Some representative examples from solar and interplanetary physics are described to demonstrate that the continuum approach to global problems (while keeping in mind the assumptions and limitations therein) can be very successful in providing insight and large scale interpretations of otherwise intractable problems in space physics.

Dryer, Murray↗
NASA NTRS1988

Droplet combustion at reduced gravity

The current work involves theoretical analyses of the effects identified, experiments in the NASA Lewis drop towers performed in the middeck areas of the Space Shuttle. In addition, there is laboratory work associated with the design of the flight apparatus. Calculations have shown that some of the test-matrix data can be obtained in drop towers, and some are achievable only in the space experiments. The apparatus consists of a droplet dispensing device (syringes), a droplet positioning device (opposing, retractable, hollow needles), a droplet ignition device (two matched pairs of retractable spark electrodes), gas and liquid handling systems, a data acquisition system (mainly giving motion-picture records of the combustion in two orthogonal views, one with backlighting for droplet resolution), and associated electronics.

Dryer, F. L.↗
NASA NTRS1988

The effect of the solenoidal condition on the numerical magnetohydrodynamic simulation of coronal dynamics

Several MHD simulations of coronal dynamics performed more than 10 years ago violated the solenoidality condition for an 'open' magnetic field topology. Using an improved code, consideration is given to the effect on the physical validity of the numerical simulation (for a representative pulse disturbance) for the case when solenoidality is deliberately violated as compared to the case when it is preserved. It is found that the error incurred in this specific case ('open' topology) in the energy density and in the plasma density profiles is rather small and, hence, does not invalidate the earlier conclusions concerning mass and wave motion.

Wu, S. T.↗
NASA NTRS1988

Interactions Between Gaseous Electrical Discharges and Single Liquid Droplets

Theoretical estimates and experimental measurements of the effects of sparks on ordered droplet motion are reported for 1-mm-diameter water and hydrocarbon droplets positioned 0.5 mm from the axis of electrodes are reported. The discussion focuses primarily on two-electrode, surge-type spark breakdowns with quasi-steady electric fields applied. Multiple electrode pairs and alternating electric fields and their effects on ordered droplet motion are also briefly discussed.

Shaw, B. D.↗
NASA NTRS1988

Expected IPS variations due to a disturbance described by a 3-D MHD model

The variations of interplanetary scintillation due to a disturbance described by a three-dimensional, time-dependent, MHD model of the interplanetary medium are calculated. The resulting simulated IPS maps are compared with observations of real disturbances and it is found that there is some qualitative agreement. It is concluded that the MHD model with a more realistic choice of input conditions would probably provide a useful description of many interplanetary disturbances.

Tappin, S. J.↗
NASA NTRS1989

Droplet combustion drop tower tests using models of the space flight apparatus

An engineering model built for droplet combustion drop tower tests is described. The model was built using a design with mechanical and electrical assemblies of the same level of complexity as they will have in flight. The model was tested for functional operation and integrated into a 5-sec drop tower. Test data obtained to date are presented together with model and test cell diagrams.

Haggard, J. B.↗
NASA NTRS1988

Application of similitude principle to the numerical simulation of solar atmospheric dynamics

Numerical simulation has become an essential part of solar physics because the complex nonlinear characteristics of solar phenomena makes analytical solutions difficult to obtain. Realistic simulation of the birth and decay of an active region still is not possible because of the wide range of spatial and time scales that must be considered. Therefore, proper scaling rules must be recognized for the development of appropriate models. In this paper, the similitude principle is applied to develop scaling rules. It is found that these rules are highly dependent on the physical nature of the specific problem under consideration. A set of 'similitude critiques' is presented for some specific physical conditions. Numerical examples of coronal dynamic response and active region dynamics are used to demonstrate these ideas.

Wu, S. T.↗
NASA NTRS1989

Three-dimensional, time-dependent MHD simulations of interplanetary plasmoids

The paper presents a three-dimensional time-dependent simulation of a solar-ejected diamagnetic plasmoid that retains its closed topology to and beyond earth. It is assumed in this case that, before entering the computational domain, the plasmoid already exists at or near the sun. A simulation is also presented for a plasmoid that is formed in the corona near the sun or in the interplanetary medium as a consequence of the reconnection of opposite-directed IMF lines. The plasma and magnetic properties of the expanding plasmoid as it moves toward an observer at 1 AU are described.

Dryer, M.↗
NASA NTRS1989

Soliton and strong Langmuir turbulence in solar flare processes

The occurrence of modulational instability in the current sheet of a solar flare is investigated. Special attention is given to the plasma microinstability in this sheet and its relation to the flare process. It is found that solitons or strong Langmuir turbulence are likely to occur in the diffusion region under solar flare conditions in which the electric resistivity could be enhanced by several orders of magnitude in the region, resulting in significant heating and stochastic acceleration of particles. A numerical example is used to demonstrate the transition of the magnetic field velocity and plasma density from the outer MHD region into the diffusive region and then back out again with the completion of the energy conversion process. This is all made possible by an increase in resistivity of four to five orders of magnitude over the classical value.

Song, M. T.↗
NASA NTRS1989

Droplet combustion experiment drop tower tests using models of the space flight apparatus

The Droplet Combustion Experiment (DCE) is an experiment that is being developed to ultimately operate in the shuttle environment (middeck or Spacelab). The current experiment implementation is for use in the 2.2 or 5 sec drop towers at NASA Lewis Research Center. Initial results were reported in the 1986 symposium of this meeting. Since then significant progress was made in drop tower instrumentation. The 2.2 sec drop tower apparatus, a conceptual level model, was improved to give more reproducible performance as well as operate over a wider range of test conditions. Some very low velocity deployments of ignited droplets were observed. An engineering model was built at TRW. This model will be used in the 5 sec drop tower operation to obtain science data. In addition, it was built using the flight design except for changes to accommodate the drop tower requirements. The mechanical and electrical assemblies have the same level of complexity as they will have in flight. The model was tested for functional operation and then delivered to NASA Lewis. The model was then integrated into the 5 sec drop tower. The model is currently undergoing initial operational tests prior to starting the science tests.

Haggard, J. B.↗
NASA NTRS1989

Multi-spacecraft testing of time-dependent interplanetary MHD models for operational forecasting of geomagnetic storms

An MHD 2-1/2D, time-dependent model is used, together with observations of six solar flares during February 3-7, 1986, to demonstrate global, large-scale, compound disturbances in the solar wind over a wide range of heliolongitudes. This scenario is one that is likely to occur many times during the cruise, possibly even encounter, phases of the Multi-Comet Mission. It is suggested that a model such as this one should be tested with multi-spacecraft data (such as the MCM and earth-based probes) with several goals in view: (1) utility of the model for operational real-time forecasting of geomagnetic storms, and (2) scientific interpretation of certain forms of cometary activities and their possible association with solar-generated activity.

Dryer, M.↗
NASA NTRS1990

Thermally conductive magnetohydrodynamic flows in helmet-streamer coronal structures

The behavior of thermally conductive plasma flows in helmet-streamer coronal structures is investigated within the framework of the axisymmetric nonrotating one-fluid MHD model. Continuous subsonic-supersonic solutions satisfying observed boundary conditions at the sun as well as the vanishing of the temperature at infinity are obtained and presented. Special attention is paid to the combined effects of conductive flow (and corresponding thermal force) and rapidly diverging magnetic field on the critical points. In this, the heliocentric distance of the neutral point determining the separation between closed and open field lines (cusp) is treated as a free parameter. These thermally conductive solutions are contrasted with those provided by corresponding isothermal models.

Cuperman, S.↗
NASA NTRS1990

N-Decane-Air Droplet Combustion Experiments in the NASA-Lewis 5 Second Zero-Gravity Facility

The burning of single fuel (n-decane) droplets in a microgravity environment (below 0.00001 of the earth's gravity, achieved in the NASA-Lewis 5-Second Zero-Gravity Facility) was studied, as part of the development of the Droplet Combustion Experiment for eventual operation aboard either the Shuttle middeck or Spacelab. Special attention is given to the combustion equipment used and its operations and performance. Temporal analysis of the local burning rates in these tests showed increasing rates of change in the local burning as droplet combustion progressed. Result point to the need of studying large droplets, with long droplet combustion lifetimes as well as low gas/droplet motion to understand reasons for this unsteadiness.

Haggard, John B.↗