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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Particle and fluid simulations of resistive current-driven electrostatic ion cyclotron waves

The results from 1-D numerical simulations of electrostatic ion cyclotron waves (EIC) are presented for a model in which the electrons are a resistive (collisional) fluid. Simulations of both the kinetic and fluid descriptions are performed and compared in order to assess the fundamental limitations of fluid theory for EIC waves. The effect of ion-neutral collisions is also included using a simple Monte Carlo technique. It is found that a small ion-neutral collision frequency destroys the frequency harmonic coupling of kinetic EIC waves and tends to validate the fluid description. The saturation amplitude of the current-driven EIC instability is in agreement with recent laboratory experiments. The coherent nature (extremely narrow spectral width) and phase velocity agree with ground based (coherent backscatter radars) and in situ observations of current-driven EIC waves in the high latitude ionosphere.

Seyler, Charles E.↗
NASA NTRS1986

A two-fluid solar wind model with Alfven waves - Parameter study and application to observations

The effects of Alfven waves from the inner corona on the solar wind density profile, flow velocity and on the random motion of protons are studied. Different base densities, temperatures, and wave velocity amplitudes, as well as different flow geometries, are considered. The model calculations are compared to simultaneous observations of the electron density profile and the resonantly scattered Lyman alpha line. Present observations, out to 4 solar radii, can be used to place limits on the coronal base density and temperature, and put an upper limit on the wave amplitude. It is pointed out that future observations of the electron density and the Lyman alpha line, out to larger heliocentric distances, and of lines from heavier elements, should be used to place more stringent constraints on the amplitudes of MHD waves in the corona.

Esser, R.↗
NASA NTRS1985

Nonlinear shock acceleration. III - Finite wave velocity, wave pressure, and entropy generation via wave damping

The nonlinear theory of shock acceleration developed in earlier papers, which treated the waves as being completely frozen into the fluid, is generalized to include wave dynamics. In the limit where damping keeps the wave amplitude small, it is found that a finite phase velocity (V sub ph) of the scattering waves through the background fluid, tempers the acceleration generated by high Mach number shocks. Asymptotic spectra proportional to 1/E sq are possible only when the ratio of wave velocity to shock velocity is less than 0.13. For a given asymptotic spectrum, the efficiency of relativistic particle production is found to be practically independent of the value of V sub ph, so that earlier results concerning its value remain valid for finite V sub ph. In the limit where there is no wave damping, it is shown that for modest Alfven Mach numbers, approximately greater than 4 and less than 6, the magnetic field is amplified by the energetic particles to the point of being in rough equipartition with them, as models of synchrotron emission frequently take the field to be. In this case, the disordering and amplification of field energy may play a major role in the shock transition.

Eichler, D.↗
NASA NTRS1966

Fluid transmission line dynamics

Computer model of fluid transmission line using digital technique to simulate transport delay associated with pressure wave propagation along fluid line

DIGITAL SIMULATION↗
DOE OSTI2022

Ocean Energy Sandia TEAMER WEC Simulation Results

Computational fluid simulations for wave energy converters and supporting materials from Ocean Energy's WEC Buoy TEAMER project in collaboration with Sandia National Laboratories. Each file includes images and video of simulation along with the simulation files for the case. The videos and images include air and water simulations of the buoy in 2D and 3D views. Data spreadsheets of the simulation outputs are also included in the files. The data are represented as different cases in which the wave height(Hs) and peak period(Tp) were different.

16 TIDAL AND WAVE POWER↗
NASA NTRS1988

Cosmic-ray transport in accelerating flows

The quasi-linear transport equation of energetic charged particles is derived, including scattering by Alfven waves propagating parallel and antiparallel to a uniform magnetic field, losses by synchrotron radiation, and acceleration of the cold background fluid supporting the waves. As in the comoving frame equations of radiative transfer, scattering, and loss terms are evaluated in the frame in which the fluid is locally at rest. The diffusion approximation is applied to the resulting equation, yielding a transport equation for the isotropic part of the distribution function and a first-order approximation to the anisotropy. The conditions under which this approximation may be applied are discussed. In the nonrelativistic regime, the standard equation of the diffusion approximation is recovered. As contributions previously investigated, new effects appear from the spatial and temporal variations of the fluid velocity as well as the synchrotron radiation terms. These are discussed in detail.

Kirk, John G.↗
DOE OSTI2020

Cold-hot coupled waves in a flowing magnetized plasma

Abstract Nonlinear coupling of cold and hot waves in a flowing magnetized plasma is analyzed with the Vlasov equation. An analytical solution is obtained for cold waves of a small amplitude (weak flow) and a long wavelength. The distribution function is obtained by integrating the kinetic equation along a perturbed phase-space trajectory for a time-varying plasma flow. The kinetic description presents a generalized dispersion relation that involves resonances depending on cold and hot wave dispersions. Coherent fluid motion leads to radiation peaks in addition to the cyclotron harmonics, where the wavenumber of the cold wave determines the peak frequencies. The peaks appear narrow when the wave propagates perpendicular to the time-averaged flow while they become broad due to the Doppler effect when the wave propagates parallel to the flow. Fully kinetic particle-in-cell simulations corroborate the theoretical predictions. The dispersion relation and resulting wave spectra provide information about plasma parameters and flow properties.

Physics↗
NASA NTRS2012

High-Speed Transport of Fluid Drops and Solid Particles via Surface Acoustic Waves

A compact sampling tool mechanism that can operate at various temperatures, and transport and sieve particle sizes of powdered cuttings and soil grains with no moving parts, has been created using traveling surface acoustic waves (SAWs) that are emitted by an inter-digital transducer (IDT). The generated waves are driven at about 10 MHz, and it causes powder to move towards the IDT at high speed with different speeds for different sizes of particles, which enables these particles to be sieved. This design is based on the use of SAWs and their propelling effect on powder particles and fluids along the path of the waves. Generally, SAWs are elastic waves propagating in a shallow layer of about one wavelength beneath the surface of a solid substrate. To generate SAWs, a piezoelectric plate is used that is made of LiNbO3 crystal cut along the x-axis with rotation of 127.8 along the y-axis. On this plate are printed pairs of fingerlike electrodes in the form of a grating that are activated by subjecting the gap between the electrodes to electric field. This configuration of a surface wave transmitter is called IDT. The IDT that was used consists of 20 pairs of fingers with 0.4-mm spacing, a total length of 12.5 mm. The surface wave is produced by the nature of piezoelectric material to contract or expand when subjected to an electric field. Driving the IDT to generate wave at high amplitudes provides an actuation mechanism where the surface particles move elliptically, pulling powder particles on the surface toward the wavesource and pushing liquids in the opposite direction. This behavior allows the innovation to separate large particles and fluids that are mixed. Fluids are removed at speed (7.5 to 15 cm/s), enabling this innovation of acting as a bladeless wiper for raindrops. For the windshield design, the electrodes could be made transparent so that they do not disturb the driver or pilot. Multiple IDTs can be synchronized to transport water or powder over larger distances. To demonstrate the transporting action, a video camera was used to record the movement. The speed of particles was measured from the video images.

Bar-Cohen, Yoseph↗
NASA NTRS1987

Nonlinear magnetohydrodynamic waves in a steady zonal circulation for a shallow fluid shell on the surface of a rotating sphere

This paper considers two-dimensional nonlinear MHD waves of large horizontal spatial scales for a thin magnetofluid layer on the surface of a rotating sphere. The 'shallow fluid' hydrodynamic equations are generalized to include the effects of magnetic fields, and it is shown that the resulting MHD equations can be reduced to a single scalar equation for a stream function involving several free functions. For special choices of these free functions, two kinds of finite-amplitude MHD waves are obtained, propagating in the azimuthal direction relative to the uniformly rotating background atmosphere in the presence of a background zonal magnetic field and a steady differential zonal flow. These two kinds of MHD waves are fundamentally due to the joint effects of the uniform rotation of the background atmosphere and background magnetic field; the first is an inertial wave of the Rossby (1939) and Haurwitz (1940) type, modified by the presence of the background zonal magnetic field, while the second is a magnetic Alfven-like wave which is modified by the uniform rotation of the background atmosphere.

Lou, Y. Q.↗
NASA NTRS1989

Kinetic effects of Alfven wave nonlinearity. I - Ponderomotive density fluctuations

The Vlasov theory is used to study kinetic corrections to fluid descriptions of Alfven wave nonlinearity. The method is to obtain an expression for the second-order perturbed distribution function produced by a nonlinear Alfven wave. From this distribution function a kinetically correct expression is obtained for the plasma density perturbation associated with an envelope-modulated Alfven wave. This kinetic theory result differs substantially from the fluid expression when the plasma beta is greater than about 1, and the electron and ion temperatures are approximately equal. This result is of interest because density fluctuations are an observationally accessible indicator of wave nonlinearity in solar system Alfven waves. It also will assist in the determination of properties of Alfven waves in the interstellar medium. Finally, this analysis also yields a kinetically correct expression for u, the magnetic field-aligned component of the plasma fluid velocity.

Spangler, Steven R.↗
DOE OSTI2024

Shock tube experiments on the three-layer Richtmyer–Meshkov instability

Here, a vertical shock tube is used for experiments on the three-layer Richtmyer–Meshkov instability. Two closely spaced membrane-less interfaces are formed by the flow of two different sects of three gases: one with air above CO 2 above SF 6 and the other with helium above air above SF 6 . The lightest of the three gases enters the shock tube at the top of the driven section and flows downward. Conversely, the heaviest gas enters at the bottom of the shock tube and flows upward while the intermediate density gas enters at the middle through porous plates. All three gases are allowed to escape through holes at the layer location, leaving an approximately 30-mm layer of intermediate-density gas suspended between the lightest gas from above and the heaviest gas from below. A single-mode, two-dimensional initial perturbation is then imposed on the lower interface by oscillating the shock tube in the horizontal direction. The flow is visualized by seeding the intermediate gas with particles and illuminating it with a pulsed laser. Image sequences are then captured using high-speed video cameras. Perturbation amplitude measurements are made from the three-layer system and compared with measurements from 2, two-layer systems. It is observed that the presence of the upper, initially flat interface produces a decrease in growth of instability amplitude in the nonlinear phase over an equivalent single-interface configuration.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2008

Magnetofluid Turbulence in the Solar Wind

The solar wind shows striking characteristics that suggest that it is a turbulent magnetofluid, but the picture is not altogether simple. From the earliest observations, a strong correlation between magnetic fluctuations and plasma velocity fluctuations was noted. The high corrections suggest that the fluctuations are Alfven waves. In addition, the power spectrum of the magnetic fluctuation showed evidence of an inertial range that resembled that seen in fully-developed fluid turbulence. Alfven waves, however, are exact solutions of the equations of incompressible magnetohydrodynamics. Thus, there was a puzzle: how can a magnetofluid consisting of Alfven waves be turbulent? The answer lay in the role of velocity shears in the solar wind that could drive turbulent evolution. Puzzles remain: for example, the power spectrum of the velocity fluctuations is less steep than the slope of the magnetic fluctuations, nor do we understand even now why the solar wind appears to be nearly incompressible with a -5/3 power-spectral index.

Goldstein, Melvyn L.↗