The modulation of low-energy proton distributions by propagating interplanetary shock waves - A numerical simulation
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Decker, R. B.↗
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A numerical simulation of two-dimensional inlet flow fields
Inlet flow fields for airbreathing missiles are calculated by the adaptation of a two-dimensional computational method developed for the flow around airfoils. A supersonic free stream is assumed to allow the forebody calculation to be uncoupled from the inlet calculation. The inlet calculation employs an implicit, time-marching finite-difference procedure to solve the thin-layer Navier-Stokes equations formulated in body-fitted coordinates. Because the method can be used for a flow field with both subsonic and supersonic regions, it is applicable to subcritical as well as supercritical inlet operation.
Biringen, S.↗
Numerical simulation of a sudden stratospheric warming with a three-dimensional, spectral, quasi-geostrophic model
An analysis of a sudden stratospheric warming which developed spontaneously during a winter simulation with a three-dimensional quasi-geostrophic model is described. Changes in the circulation and thermal structure of the winter polar stratosphere that occurred during the warming are shown to be in close agreement with observed behavior: enhanced vertical flux of eddy energy into the stratosphere, rapid temperature increase in high latitudes with a reversal of the zonal mean temperature gradient between midlatitude and pole, destruction of the circumpolar cyclonic vortex, and a marked deceleration of the westerly jet and the appearance of zonal mean easterlies. Energies of the warming are also consistent with observed characteristics. Many aspects of the dynamical development of the present model simulation are shown to agree with a previous model simulation, but there are also areas of disagreement.
Grose, W. L.↗
Numerical simulation of plasma insulator interactions in space. Part 1: The self consistent calculation
A computer program is being developed to simulate the interaction of a plasma with a conducting disk partially covered by an insulator. Initial runs consider only charge sticking to the dielectric. Results indicate that the current density drawn by the hole in the dielectric increases approximately linearly with voltage for conductor voltages between 5 volts and 250 volts.
Nonnast, J. H.↗
Numerical simulation of plasma insulator interactions in space. Part 2: Dielectric effects
Any process which may be modeled statistically for a simple plasma particle may be modeled by the particle in cell technique. The success of the calculation is then dependent on having a large enough number of particles that the statistical treatment is meaningful. Thus it is possible to include the effects of secondary emission, backscattering, charge sticking and possibly dielectric breakdown, photoemission, and spallation. The first plasma dielectric interaction included in the computer code for simulating plasma insulator interactions is secondary electron emission. A calculated current density vs. voltage curve is presented and compared to an experimental curve.
Chaky, R. C.↗
Numerical simulation of the magnetospheric gate model for X-ray bursters
A Lagrangian, fully implicit, one dimensional hydrodynamic computer code was used to investigate the evolution of a gas cloud impacting the surface of a 20 km, 1 Msub solar neutron star. This gas is initially at rest with respect to the surface of the neutron star, extends to 185 km above the surface, and is optically thick. The infall results in a burst which lasts about 0.1 seconds and reached a peak luminosity and effective temperature of 240,000 Lsub solar and 9 million; respectively. The burst was followed by a phase of oscillations with a period 0.2 seconds.
Starrfield, S. G.↗
Numerical simulation of sheath structure and current-voltage characteristics of a conductor-dielectric disk in a plasma
A computer program is being developed to simulate the interaction of a plasma with a conducting disk. Two configurations are examined: (1) the conductor is a 'button' in the center of a larger dielectric disk, and (2) the conducting disk is covered by a dielectric disk to the same size with a circular hole in the center of the dielectric, exposing a region of conductor. Results of the electrostatic plasma simulation are presented both with and without secondary electron emission from the dielectric; characteristic curves and voltage profiles are included.
Chaky, R. C.↗
Numerical simulation of the interaction of the plasma sheet with the lobes of the earth's magnetotail
(Previously announced in STAR as N82-16634)
Swift, D. W.↗
Numerical simulations of unsteady transonic flow in diffusers
Forced and naturally occurring, self-sustaining oscillations of transonic flows in two-dimensional diffusers were computed using MacCormack's hybrid method. Depending upon the shock strengths and the area ratios, the flow was fully attached or separated by either the shock or the adverse pressure gradient associated with the enlarging diffuser area. In the case of forced oscillations, a sinusoidal plane pressure wave at frequency 300 Hz was prescribed at the exit. A sufficiently large amount of data were acquired and Fourier analyzed. The distrbutions of time-mean pressures, the power spectral density, and the amplitude with phase angle along the top wall and in the core region were determined. Comparison with experimental results for the forced oscillation generally gave very good agreement; some success was achieved for the case of self-sustaining oscillation despite substantial three-dimensionality in the test. An observation of the sequence of self-sustaining oscillations was given.
Liou, M.-S.↗
Critical review of the trailing edge condition in steady and unsteady flow. Blade flutter in compressors and fans: Numerical simulation of the aerodynamic loading
Existing interpretations of the trailing edge condition, addressing both theoretical and experimental works in steady, as well as unsteady flows are critically reviewed. The work of Kutta and Joukowski on the trailing edge condition in steady flow is reviewed. It is shown that for most practical airfoils and blades (as in the case of most turbomachine blades), this condition is violated due to rounded trailing edges and high frequency effects, the flow dynamics in the trailing edge region being dominated by viscous forces; therefore, any meaningful modelling must include viscous effects. The question of to what extent the trailing edge condition affects acoustic radiation from the edge is raised; it is found that violation of the trailing edge condition leads to significant sound diffraction at the tailing edge, which is related to the problem of noise generation. Finally, various trailing edge conditions in unsteady flow are discussed, with emphasis on high reduced frequencies.
Radwan, S. F.↗
The sensitivity of numerically simulated climates to land-surface boundary conditions
Eleven sensitivity experiments that were made with general circulation models to see how land-surface boundary conditions can influence the rainfall, temperature, and motion fields of the atmosphere are discussed. In one group of experiments, different soil moistures or albedos are prescribed as time-invariant boundary conditions. In a second group, different soil moistures or different albedos are initially prescribed, and the soil moisture (but not the albedo) is allowed to change with time according to the governing equations for soil moisture. In a third group, the results of constant versus time-dependent soil moistures are compared.
Mintz, Y.↗
Numerical Simulation for Droplet Combustion Using Lagrangian Hydrodynamics
A predictive model of spray combustion must incorporate models for the wide variety of physical environments in a practical combustor. In regions where droplets are closely spaced, combustion resembles a diffusion flame; where they are well separated, an envelope or wake flame results. The relative velocity field between the fuel droplets and oxidizer in influences boundary layer development about the droplet, recirculating flow patterns, and droplet shape and stability. A model must encompass these interacting temporal and spatial effects as well as complicated combustor boundaries. The objective of the current work is to develop the triangular gridding method for describing the individual and collective properties of vaporizing and burning fuel droplets.
Fritts, M. J.↗
Numerical simulation of vortex breakdown by the vortex-filament method
The vortex filament method was applied to the simulation of vortex breakdown. The principal vortex region was represented by multiple filaments, and an axial velocity component was induced by a spiral winding of the filaments. First, an accuracy check was performed for a cylindrical swirling flow with simple analytical expressions for the axial and theta velocities. The result suggests that the flow field is simulated to any accuracy by increasing the number of filaments. Second, an axisymmetric type vortex breakdown was simulated, with experimental data serving as upstream conditions. The calculated axial and theta velocity contours show the breakdown of the vortex, including a rapid change in the vortex core, followed axially by a recovery zone and then a second breakdown. When three dimensional initial data are used the second breakdown appears to be of the spiral type in correspondence with experimental observations. The present method is easily used to simulate other types of vortex breakdown or other vortex flows with axial velocity.
Nakamura, Y.↗
Numerical simulation of soil brightness temperatures at wavelength of 21 cm
A simulation model is applied to reproduce some observed brightness temperatures at a wavelength of 21 cm. The simulated results calculated with two different soil textures are compared directly with observations measured over fields in Arizona and South Dakota. It is found that good agreement is possible by properly adjusting the surface roughness parameter. Correlation analysis and linear regression of the brightness temperatures versus soil moistures are also carried out.
Mo, T.↗
Turbulent structures in wall-bonded shear flows observed via three-dimensional numerical simulations
(Previously announced in STAR as N80-29622)
Leonard, A.↗
A numerical simulation of soil temperature and moisture variations for a bare field
The diurnal variations of soil temperature and moisture content were simulated for a bare agricultural field in the San Joaquin Valley in California. The simulation pertained to the first 72 hours of drying, from saturation, of a sandy, clay loam soil. The results were compared with measurements of soil temperature and moisture content made at the field. Calculated and measured values of soil temperature trends agreed in general, but model results of moisture trends did not replicate observed diurnal effects evident at depths 4 centimeters or more below the surface.
Schieldge, J. P.↗
Numerical simulation of steady supersonic flow over spinning bodies of revolution
A recently reported parabolized Navier-Stokes code has been employed to compute the supersonic flowfield about a spinning cone and spinning and nonspinning ogive cylinder and boattailed bodies of revolution at moderate incidence. The computations were performed for flow conditions where extensive measurements for wall pressure, boundary-layer velocity profiles, and Magnus force had been obtained. Comparisons between the computational results and experiment indicate excellent agreement for angles of attack up to 6 deg. At angles greater than 6 deg discrepancies are noted which are tentatively attributed to turbulence modeling errors. The comparisons for Magnus effects show that the code accurately predicts the effects of body shape for the selected models.
Sturek, W. B.↗
Numerical simulations of the decay of satellite galaxy orbits
A multiple three-body technique is used to study the orbital evolution of satellite galaxies which is similar to the N-body method but neglects two-body forces between stars in the halo of the parent galaxy. It is found that, for satellites orbiting within the halo, Chandrasekhar's (1960) dynamical friction formula accurately describes the orbital decay rate, including its variation with satellite mass and size and with the number density and mass of halo stars. Significant frictional forces are present even outside the halo, and the orbital decay rate, instead of depending on the procedure used to place the satellite in its orbit, is determined only by the current orbital parameters. This semirestricted N-body method is sufficiently fast to have permitted the running of 200 simulations to date, many more than would have been possible by means of the conventional N-body technique.
Lin, D. N. C.↗