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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 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Least-Squares Spectral Element Solutions to the CAA Workshop Benchmark Problems

This paper presents computed results for some of the CAA benchmark problems via the acoustic solver developed at Rocketdyne CFD Technology Center under the corporate agreement between Boeing North American, Inc. and NASA for the Aerospace Industry Technology Program. The calculations are considered as benchmark testing of the functionality, accuracy, and performance of the solver. Results of these computations demonstrate that the solver is capable of solving the propagation of aeroacoustic signals. Testing of sound generation and on more realistic problems is now pursued for the industrial applications of this solver. Numerical calculations were performed for the second problem of Category 1 of the current workshop problems for an acoustic pulse scattered from a rigid circular cylinder, and for two of the first CAA workshop problems, i. e., the first problem of Category 1 for the propagation of a linear wave and the first problem of Category 4 for an acoustic pulse reflected from a rigid wall in a uniform flow of Mach 0.5. The aim for including the last two problems in this workshop is to test the effectiveness of some boundary conditions set up in the solver. Numerical results of the last two benchmark problems have been compared with their corresponding exact solutions and the comparisons are excellent. This demonstrates the high fidelity of the solver in handling wave propagation problems. This feature lends the method quite attractive in developing a computational acoustic solver for calculating the aero/hydrodynamic noise in a violent flow environment.

Lin, Wen H.↗
NASA NTRS2017

Pisgah Lava Cave Communication Test: Science Case Study for the Networked Constellations Initiative

As part of the science case study for the Networked Constellations initiative, a team of JPL scientists explore the possibility of a mission to study the lava caves on Mars. Natural caves on Mars and the Moon present a unique opportunity to learn about the planetary geology and to provide a shelter for human explorers. Due to power and communication challenges, a network of assets has significant advantages over a single asset sent inside a cave. However, communication between the assets and the data downlink present significant difficulties due to the presence of rough walls, boulders, and other obstacles with unknown dielectric constant inside a typical cave, disturbing the propagation of the radio waves. A detailed study is needed to establish the limitations of the current communication technologies and to develop requirements for the new communication technology applicable to the cave environment. On May 4 of 2017, Konstantin Belov, Doug Ellison, and Abby Fraeman visited a lava cave in Pisgah, CA. The purpose of the visit was to build a 3D map of the cave, which could be used to create a model of radio wave propagation, and to conduct a series of communication tests using off-the-shelf equipment to verify the in-cave communication challenges. This experiment should be considered as a simple 'proof of concept' and is the subject of this report.

Belov, K.↗
NASA NTRS1986

Whistler-mode radiation from the Spacelab 2 electron beam

During the Spacelab 2 mission the Plasma Diagnostics Package (PDP) performed a fly-around of the Shuttle at distances of up to 300 meters while an electron beam was being ejected from the Shuttle. A magnetic conjunction of the Shuttle and the PDP while the electron gun was operating in a steady (DC) mode is discussed. During this conjunction, the PDP detected a clear funnel-shaped emission that is believed to be caused by whistler-mode emission from the beam. Ray-path calculations show that the shape of the funnel can be accounted for by whistler-mode waves propagating near the resonance cone. Because the beam and waves are propagating in the same direction, the radiation must be produced by a Landau interaction with the beam. Other types of waves generated by the beam are also described.

Gurnett, D. A.↗
NASA NTRS1993

The Generation of Oblique Magnetosonic Waves

One of the outstanding issues regarding the excitation of magnetosonic waves has been the observational evidence that obliquely propagating waves are dominant at comets and planetary foreshocks despite the predictions of linear theory that maximum growth occurs at parallel propagation. To address this issue, we have conducted a detailed linear theory using a beam-ring distribution function. The results have shown that such distribution functions are associated with four separate instabilities. Two of these instabilities are similar to the right hand resonant ion/ion and the non-resonant instabilities which are also present in the case of a field aligned beam. The other two instabilities are associated with the presence of ring part of the distribution function. One of these instabilities excites magnetosonic waves with maximum growth in the oblique directions. The other excites Alfven waves with maximum growth in the oblique directions. The importance of the former instability is that it may explain the oblique nature of the magnetosonic waves observed at planetary foreshocks and comets. In order to understand the nonlinear properties of these various instabilities, we have also conducted 2-D hybrid (particle ions, fluid electrons) simulations. We have found that when the beam density is sufficiently large so that the non-resonant instability has the largest growth rate, these waves dominate the initial wave power in the system. At later times, however, the obliquely propagating magnetosonic waves become dominant. Another important finding was that when the two instabilities which excite magnetosonic waves have the largest growth rates, the system is dominated by the obliquely propagating magnetosonic waves. This is despite the fact that the largest growth rate for one of the instabilities occurs in the parallel direction. The exact cause of this is not currently understood and is under investigation.

Source record↗
NASA NTRS1992

Results of a zonally truncated three-dimensional model of the Venus middle atmosphere

Although the equatorial rotational speed of the solid surface of Venus is only 4 m s(exp-1), the atmospheric rotational speed reaches a maximum of approximately 100 m s(exp-1) near the equatorial cloud top level (65 to 70 km). This phenomenon, known as superrotation, is the central dynamical problem of the Venus atmosphere. We report here the results of numerical simulations aimed at clarifying the mechanism for maintaining the equatorial cloud top rotation. Maintenance of an equatorial rotational speed maximum above the surface requires waves or eddies that systematically transport angular momentum against its zonal mean gradient. The zonally symmetric Hadley circulation is driven thermally and acts to reduce the rotational speed at the equatorial cloud top level; thus wave or eddy transport must counter this tendency as well as friction. Planetary waves arising from horizontal shear instability of the zonal flow (barotropic instability) could maintain the equatorial rotation by transporting angular momentum horizontally from midlatitudes toward the equator. Alternatively, vertically propagating waves could provide the required momentum source. The relative motion between the rotating atmosphere and the pattern of solar heating, which as a maximum where solar radiation is absorbed near the cloud tops, drives diurnal and semidiurnal thermal tides that propagate vertically away from the cloud top level. The effect of this wave propagation is to transport momentum toward the cloud top level at low latitudes and accelerate the mean zonal flow there. We employ a semispectral primitive equation model with a zonal mean flow and zonal wavenumbers 1 and 2. These waves correspond to the diurnal and semidiurnal tides, but they can also be excited by barotropic or baroclinic instability. Waves of higher wavenumbers and interactions between the waves are neglected. Symmetry about the equator is assumed, so the model applies to one hemisphere and covers the altitude range 30 to 110 km. Horizontal resolution is 1.5 deg latitude, and vertical resolution is 1.5 km. Solar and thermal infrared heating, based on Venus observations and calculations drive the model flow. Dissipation is accomplished mainly by Rayleigh friction, chosen to produce strong dissipation above 85 km in order to absorb upward propagating waves and limit extreme flow velocities there, yet to give very weak Rayleigh friction below 70 km; results in the cloud layer do not appear to be sensitive to the Rayleigh friction. The model also has weak vertical diffusion, and very weak horizontal diffusion, which has a smoothing effect on the flow only at the two grid points nearest the pole.

Newman, M.↗
NASA NTRS2016

MAVEN Observation of an Obliquely Propagating Low-Frequency Wave Upstream of Mars

We report Mars Atmosphere and Volatile EvolutioN (MAVEN) mission observations of a large amplitude low-frequency plasma wave that propagated oblique to the ambient magnetic field upstream of Mars along with a non-solar-wind plasma component that had a flow velocity perpendicular to the magnetic field. We consider nine possibilities for this wave that include various combinations of its propagation direction, polarization in the solar wind frame, and ion source responsible for its generation. Using the observed wave parameters and the measured plasma parameters as constraints, we uniquely identify the wave by systematically discarding these possibilities. We determine that the wave is a right-hand polarized wave that propagated upstream in the solar wind frame. We find two possibilities for the ion source that can be responsible for this wave generation. They are either newly born pickup protons or reflected solar wind protons from the bow shock.We determine that the observed non-solar-wind component is not responsible for the wave generation, and it is likely that the non-solar-wind component was merely perturbed by the passage of the wave.

low frequency wave↗
NASA NTRS1967

Experiments in low energy plasmas

Electron energy loss in afterglow plasmas, plasma transport and stability and electromagnetic wave propagation through magnetoplasmas

MAGNETOPLASMA↗