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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 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Surface tension and bubble shapes in a partially filled rotating cylinder under low gravity

A computer algorithm is developed to simulate the profile of a free liquid surface for a cylindrical container partially filled with a Newtonian fluid of constant density, rotating about its axis of symmetry. The equilibrium shape of the free surface is governed by a balance of capillary, centrifugal, and gravity forces. The results can be used to determine the profile of a bubble at various rotating speeds under the gravity environments from low gravity, microgravity to zero-gravity. The present paper discusses the further extension of the study of the determination of bubble shape in a higher rotating speed container developed by Hung and Leslie.

Hung, R. J.↗
NASA NTRS1988

Bow shocks and bubbles are seen around hot stars by IRAS

Examination of the IRAS all-sky imagery reveals extended, arcuate, and ringlike features associated with hot luminous stars. They fall into a number of classes: stellar wind bow shocks, stellar wind bubbles, dust shells, dust heated by isolated B stars, bright rims, and dust in H II regions. Here, some objects are discussed in which the star exercises structural control over the spatial distribution of dust: bow shocks, bubbles, and radiation pressure-driven shells. A list of the 15 most prominent objects is presented, a few prototypes are shown, and their characteristics are explained in terms of thermal emission processes and gasdynamics.

Van Buren, Dave↗
NASA NTRS1988

Microgravity bubble migration in rotating flows

The NASA KC-135 microgravity-environment aircraft was used to gather experimental data on the migration of bubbles in rotating liquid fields under reduced gravity conditions. The data thus obtained were compared to those of an analysis for the prediction of fluid particle trajectories in the presence of both gravitational and rotational fields at the limit of quasi-steady creeping flow. Reasonable agreement with experimental results was achieved, despite the large size of the bubbles, their close proximity to a bounding surface over significant portions of their migration time, and their rather nonspherical geometry.

Ruggles, J. S.↗
NASA NTRS1989

Non-Contact Temperature Requirements (NCTM) for drop and bubble physics

Many of the materials research experiments to be conducted in the Space Processing program require a non-contaminating method of manipulating and controlling weightless molten materials. In these experiments, the melt is positioned and formed within a container without physically contacting the container's wall. An acoustic method, which was developed by Professor Taylor G. Wang before coming to Vanderbilt University from the Jet Propulsion Laboratory, has demonstrated the capability of positioning and manipulating room temperature samples. This was accomplished in an earth-based laboratory with a zero-gravity environment of short duration. However, many important facets of high temperature containerless processing technology have not been established yet, nor can they be established from the room temperature studies, because the details of the interaction between an acoustic field an a molten sample are largely unknown. Drop dynamics, bubble dynamics, coalescence behavior of drops and bubbles, electromagnetic and acoustic levitation methods applied to molten metals, and thermal streaming are among the topics discussed.

Hmelo, Anthony B.↗
NASA NTRS1990

A large bubble around the Crab Nebula

IRAS and 21 cm observations of the interstellar medium around the Crab nebula show evidence of a large bubble surrounded by a partial shell. If located at the canonical 2 kpc distance of the Crab pulsar, the shell is estimated to have a radius of about 90 pc and to contain about 50,000 solar masses of swept-up gas. The way in which interior conditions of this bubble can have important implications for observations of the Crab are described, and the fashion in which presupernova evolution of the pulsar progenitor has affected its local environment is described.

Romani, Roger W.↗
NASA NTRS1990

The structure and dynamics of bubble-type vortex breakdown

A unique discrete form of the Navier-Stokes equations for unsteady, three-dimensional, incompressible flow has been used to study vortex breakdown numerically. A Burgers-type vortex was introduced along the central axis of the computational domain, and allowed to evolve in space and time. By varying the strength of the vortex and the free stream axial velocity distribution, using a previously developed Rossby number criterion as a guide, the location and size of the vortex breakdown region was controlled. While the boundaries of the vortex breakdown bubble appear to be nominally symmetric, the internal flow field is not. Consequently, the mechanisms for mixing and entrainment required to sustain the bubble region are different from those suggested by earlier axisymmetric models. Results presented in this study, for a Reynolds number of 200, are in good qualitative agreement with higher Reynolds number experimental observations, and a variety of plots have been presented to help illuminate the fluid physics.

Spall, R. E.↗
NASA NTRS1990

Stability and slosh wave for rotating bubble due to gravity-jitters under microgravity

Time-dependent fluid behaviors in microgravity environments are examined with particular attention given to the dynamics of bubble configurations. The initial bubble profiles, computed from the steady-state formulation, are used as the initial input for the time dependent computation. The parameters considered are liquid density and its kinematic viscosity, gas density and its kinematic viscosity, surface tension coefficient, angular velocity, and gravity environment. This computer algorithm can be used to simulate the fluid behavior in a microgravity environment, in particular the excitation of slosh waves due to different frequencies of gravity jitters. Results show that lower-frequency gravity jitters excite slosh waves with a higher ratio of maximum amplitude to wave length than that of the slosh waves generated by the higher frequency gravity jitters.

Hung, R. J.↗
NASA NTRS1990

Experiments on a separation bubble over an Eppler 387 airfoil at low Reynolds numbers using thin-film arrays

Experiments carried out at the NASA Langley Low-Turbulence Pressure Tunnel on an Eppler 387 airfoil at several angles of attack for Reynolds numbers of 100,000 to 300,000 are discussed. Cross-correlations and phase diagrams are used in calculating velocities, while spectra are used in checking for amplified frequencies, and coherence plots for causality. Hot-film measurements, oil-flow visualization, pressure measurements, and Drela code are compared for finding the leading and trailing edges of the bubble. It is observed that all methods agree in showing the beginning and end of the separation bubble, the velocity measurements agree in magnitude for the lower velocities, and wave packets appear in the cross-correlation.

Mousseux, Marc C.↗
NASA NTRS1992

Helium bubble flow visualization of the spanwise separation on a NACA 0012 with simulated glaze ice

Research was performed to experimentally visualize and document the flow separation due to simulated glaze ice accretion on a NACA 0012 semispan with 30 deg sweep using helium bubbles as flow tracers. Results are compared to Navier-Stokes computational simulations for different angles of attack. Prior to acquiring data for the semispan model, a two dimensional experiment was conducted to determine the accuracy of using the helium bubbles as flow tracers. Results from the three dimensional experiment compare well to the computational simulations.

Kerho, M.↗
NASA NTRS1992

Measuring the surface tension of soap bubbles

The objectives are for students to gain an understanding of surface tension, to see that pressure inside a small bubble is larger than that inside a large bubble. These concepts can be used to explain the behavior of liquid foams as well as precipitate coarsening and grain growth. Equipment, supplies, and procedures are explained.

Sorensen, Carl D.↗
NASA NTRS1992

Helium bubble flow visualization of the spanwise separation on a NACA 0012 with simulated glaze ice

Research has been performed to experimentally visualize and document the flow separation due to simulated glaze ice accretion on a NACA 0012 semispan with 30-deg sweep using helium bubbles as flow tracers. Results are compared to Navier-Stokes computational simulations for different angles of attack. Prior to acquiring data for the semispan model, a two-dimensional experiment was conducted to determine the accuracy of using the helium bubbles as flow tracers. Results from the 3D experiment compare well to the computational simulations.

Kerho, M.↗
NASA NTRS1992

Completing the evolution of supernova remnants and their bubbles

The filling fraction of hot gas in the ISM is reexamined with new calculations of the very long term evolution of SNRs and their fossil hot bubbles. Results are presented of a 1D numerical solution of the evolution of an SNR in a homogeneous medium with a nonthermal pressure corresponding to a 5-micro-G magnetic field and density of 0.2/cu cm. Comparison is made with a control simulation having no magnetic field pressure. It is found that the evolutions, once they have become radiative, differ in several significant ways, while both differ appreciably from qualitative pictures presented in the past. Over most of the evolution of either case, the hot bubble in the interior occupies only a small fraction of the shocked volume, the remainder in a thick shell of slightly compressed material. Column densities and radial distributions of O VI, N V, C IV, and Si IV as well as examples of absorption profiles for their strong UV lines are presented.

Slavin, Jonathan D.↗
NASA NTRS1992

The velocity-distance relation for galaxies on a bubble

The characteristic diameter of the most prominent void in the redshift survey of de Lapparent et al. (1986) is measured. Distances and peculiar velocities to individual galaxies are derived, and it is shown that the void is approximately a 'Hubble Bubble' in which the near and far edges are separating with the general expansion of the universe. At the 3 sigma level, infall toward the Coma cluster is detected for a portion of the bubble wall. Limits on the net outflow from the void and infall into Coma are used to estimate Omega.

Bothun, Gregory D.↗
NASA NTRS1992

Discrete-vortex simulation of pulsating flow on a turbulent leading-edge separation bubble

Studies are made of the turbulent separation bubble in a two-dimensional semi-infinite blunt plate aligned to a uniform free stream with a pulsating component. The discrete-vortex method is applied to simulate this flow situation because this approach is effective for representing the unsteady motions of the turbulent shear layer and the effect of viscosity near the solid surface. The numerical simulation provides reasonable predictions when compared with the experimental results. A particular frequency with a minimum reattachment is related to the drag reduction. The most effective frequency is dependent on the amplified shedding frequency. The turbulent flow structure is scrutinized. This includes the time-mean and fluctuations of the velocity and the surface pressure, together with correlations between the fluctuating components. A comparison between the pulsating flow and the non-pulsating flow at the particular frequency of the minimum reattachment length of the separation bubble suggests that the large-scale vortical structure is associated with the shedding frequency and the flow instabilities.

Sung, Hyung Jin↗
NASA NTRS1992

An axisymmetric magnetohydrodynamic model for the Crab pulsar wind bubble

We extend Kennel and Coroniti's (1984) spherical magnetohydrodynamic models for the Crab Nebula to include the pinching effect of the toroidal magnetic field. Since the bulk nebular flow is likely to be very submagnetosonic, a quasi-static treatment is possible. We show that the pinching effect can be responsible for the observed elongation of the pulsar wind bubble, as indicated by the surface brightness contours of optical synchrotron radiation. From the observed elongation we estimate a value for sigma, the ratio of Poynting flux to plasma kinetic energy flux in the free pulsar wind, which is consistent with previous results from spherical models. Using the inferred magnetic field configuration inside the pulsar wind bubble, combined with the observed dimensions of the X-ray nebula, we are able to constrain the particle distribution function. We conclude that, for a power-law injection function, the maximum energy has to be much larger in the pulsar equatorial region than in the polar region.

Begelman, Mitchell C.↗
NASA NTRS1992

Formation of the dark bays in the Crab optical synchrotron nebula - Is the Crab pulsar wind bubble interacting with its progenitor's wind?

Models are presented for the formation of the two dark bays in the Crab optical synchrotron nebula, from which the optical synchrotron-emitting particles seem to be excluded. It is proposed that the bays are formed by the advance of the Crab pulsar's wind bubble into an ambient medium possessing a stratified density distribution with higher density in the plane of the bays than in other directions. The ambient density and degree of stratification required to produce the bays depends on whether the medium consists of a general interstellar medium, a progenitor stellar wind, or fast-moving supernova ejecta. In the case of an interstellar medium, the bays would be expected to move apart much more slowly than observed, and the required density would have to be implausibly high. It is concluded that the pulsar wind bubble is probably interacting with the slow wind from its progenitor, and it is shown that bays formed in this way agree with the observations reasonably well.

Li, Zhi-Yun↗
NASA NTRS1993

The Geminga supernova as a possible cause of the Local Interstellar Bubble

It is proposed that the Local Bubble was caused by the SN that produced the Geminga pulsar. The pulsar's 300,000-year age is used in conjunction with the motion of a recently discovered optical counterpart to verify that the SN was well-positioned for production of the Local Bubble if the explosion occurred within 60 pc of the solar system.

Gehrels, Neil↗