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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

On the generation of a bubbly universe - A quantitative assessment of the CfA slice

A first attempt is made to calculate the properties of the matter distribution in a universe filled with overlapping bubbles produced by multiple explosions. Each spherical shell follows the cosmological Sedov-Taylor solution until it encounters another shell. Thereafter, mergers are allowed to occur in pairs on the basis of N-body results. At the final epoch, the matrix of overlapping shells is populated with 'galaxies' and the properties of slices through the numerically constructed cube compare well with CfA survey results for specified initial conditions. A statistic is found which measures the distance distribution from uniformly distributed points to the nearest galaxies on the projected plane which appears to provide a good measure of the bubbly character of the galaxy distribution. In a quantitative analysis of the CfA 'slice of the universe', a very good match is found between simulation and the real data for final average bubble radii of (13.5 + or - 1.5)/h Mpc with formal filling factor 1.0-1.5 or actual filling factor of 65-80 percent.

Ostriker, J. P.↗
NASA NTRS1989

Cosmic structure from radiation-blown bubbles

Absorbing material in an expanding universe filled with sources of radiation is subject to an instability driven by radiation pressure. In the optically thick limit, this instability takes the form of rapidly growing cavities or bubbles in the absorbing material. No matter how small they are when they begin, such bubbles grow to approach a limiting size which depends only on the ratio of photon pressure to absorber inertia. For a nonprimordial submillimeter radiation background as strong as that recently detected by the Berkely-Nagoya group, the bubbles grow to a comoving radius of about 20 Mpc, comparable in scale to the voids seen in the large-scale galaxy distribution.

Hogan, Craig J.↗
NASA NTRS1989

Venous gas embolism - Time course of residual pulmonary intravascular bubbles

A study was carried out to determine the time course of residual pulmonary intravascular bubbles after embolization with known amounts of venous air, using an N2O challenge technique. Attention was also given to the length of time that the venous gas emboli remained as discrete bubbles in the lungs with 100 percent oxygen ventilation. The data indicate that venous gas emboli can remain in the pulmonary vasculature as discrete bubbles for periods lasting up to 43 + or - 10.8 min in dogs ventilated with oxygen and nitrogen. With 100 percent oxygen ventilation, these values are reduced significantly to 19 + or - 2.5 min.

Butler, B. D.↗
NASA NTRS1989

Analysis of low Reynolds number separation bubbles using semiempirical methods

The formation and growth of transitional separation bubbles can significantly affect boundary-layer development on airfoils operating at low chord Reynolds numbers. Of primary concern is the change in boundary-layer thickness between laminar separation and turbulent reattachment. This can be estimated using semiempirical methods, such as the one devised by Horton (1968), which are based on solutions to the integral forms of the boundary-layer equations. The applicability of these methods at low Reynolds numbers was investigated using hot-wire measurements of bubbles formed on an NACA 66(3)-018 airfoil at chord Reynolds numbers of 50,000-200,000. The momentum thickness growth between separation and transition was found to be similar to that predicted for a laminar half-jet and appears to be influenced by the momentum thickness Reynolds number at separation. This parameter also was found to have a noticeable effect on the Reynolds number based on the length of a bubble's laminar portion.

Schmidt, Gordon S.↗
NASA NTRS1990

A computational efficient modelling of laminar separation bubbles

In predicting the aerodynamic characteristics of airfoils operating at low Reynolds numbers, it is often important to account for the effects of laminar (transitional) separation bubbles. Previous approaches to the modelling of this viscous phenomenon range from fast but sometimes unreliable empirical correlations for the length of the bubble and the associated increase in momentum thickness, to more accurate but significantly slower displacement-thickness iteration methods employing inverse boundary-layer formulations in the separated regions. Since the penalty in computational time associated with the more general methods is unacceptable for airfoil design applications, use of an accurate yet computationally efficient model is highly desirable. To this end, a semi-empirical bubble model was developed and incorporated into the Eppler and Somers airfoil design and analysis program. The generality and the efficiency was achieved by successfully approximating the local viscous/inviscid interaction, the transition location, and the turbulent reattachment process within the framework of an integral boundary-layer method. Comparisons of the predicted aerodynamic characteristics with experimental measurements for several airfoils show excellent and consistent agreement for Reynolds numbers from 2,000,000 down to 100,000.

Dini, Paolo↗
NASA NTRS1989

Analytic theory for the determination of velocity and stability of bubbles in a Hele-Shaw cell. I - Velocity selection. II - Stability

An asymptotic theory is presented for the determination of velocity and linear stability of a steady symmetric bubble in a Hele-Shaw cell for small surface tension. First the bubble velocity relative to the fluid velocity at infinity is determined for small surface tension by means of a transcendentally small correction to the asymptotic series solution. In addition, a linear stability analysis shows that only the solution branch corresponding to the largest possible bubble velocity for given surface tension is stable, while all the others are unstable.

Tanveer, S.↗
NASA NTRS1989

Numerical simulation of thermocapillary bubble migration under microgravity for large Reynolds and Marangoni numbers

A numerical procedure in which the Navier-Stokes equations are discretized using tightly coupled discretizations of pressure derivatives and continuity equations is used here to extend the range of known terminal velocities of gaseous bubbles in liquids well beyond that in previous investigations. Computations performed for Reynolds numbers up to 2000 and Marangoni numbers up to 1000 show only a modest variation of the scaled bubble velocity between 0.16 and 0.5. The bubble velocity is influenced more by the Marangoni number than by the Reynolds number.

Balasubramaniam, R.↗
NASA NTRS1990

Measurements in a separation bubble on an airfoil using laser velocimetry

An experimental investigation was conducted to measure the reverse flow within the transitional separation bubble that forms on an airfoil at low Reynolds numbers. Measurements were used to determine the effect of the reverse flow on integrated boundary-layer parameters often used to model the bubble. Velocity profile data were obtained on an NACA 663-018 airfoil at angle of attack of 12 deg and a chord Reynolds number of 140,000 using laser Doppler and single-sensor hot-wire anemometry. A new correlation is proposed based on zero velocity position, since the Schmidt (1986) correlations fail in the turbulent portion of the bubble.

Fitzgerald, Edward J.↗
NASA NTRS1990

Co-operative oscillations of bubbles

A closed cryogenic storage tank in space may contain several bubbles. It is shown that these bubbles can oscillate in volume with n-1 resonant frequencies for n bubbles. The resonances can be excited by a sudden change in pressure, such as withdrawing fluid or venting, or by motion of the vehicle. In situations in which the ac accelerations dominate, such as in large space structures, the potential for harmful coupling of these oscillations to the spacecraft structure must be examined. Experimental data are presented which support the theoretical predictions.

Snyder, H. A.↗
NASA NTRS1991

Doppler detection of decompression bubbles with computer assisted digitization of ultrasonic signals

The use of an inexpensive, commercially available audio digitizer in conjunction with a PC to digitize Doppler bubble signals for visual and electronic evaluation is reported. This device can be operated simultaneously with Doppler audio monitoring. Precordial and arterial Doppler recordings of gas bubbles were obtained from anesthetized dogs after intravascular infusion or following decompression. Additional evaluations were conducted on Doppler bubble recordings obtained from human decompression studies. The device can be used in real-time or for later signal analysis. Accompanying menu-driven software provides for numerous signal modification options and visual displays. This device can provide a simultaneous visual display of Doppler signals normally available only for audio evaluation.

Butler, B. D.↗
NASA NTRS1993

Study Of Bubble-Count Measurement Of Surface Tension

Report presents study of bubble-count method of measurement of surface or interfacial tension of liquids. In method, gas or liquid pumped at known rate along capillary tube. One end of tube open and immersed in liquid that wets tube. Pumped gas or liquid forms bubbles, detaching themselves from immersed open end of tube, and one measures average period, Pi, for formation and detachment of bubbles.

Nishioka, Gary M.↗
NASA NTRS1993

Three-Dimensional Magnetic-Bubble Memory System

Proposed magnetic-bubble memory system includes stack of two-dimensional memory modules. Design enables overall storage density of system to be greater than prior magnetic-bubble memories. Provides nonvolatile storage, with readout access times in millisecond range. Has partly parallel input/output configuration supporting high-performance computing. Also relatively invulnerable to damage by ionizing radiation. Binary data, as represented by direction of magnetization of magnetic bubbles, reads out via Faraday effect.

Katti, Romney R.↗
NASA NTRS1994

Bubble dynamics, two-phase flow, and boiling heat transfer in a microgravity environment

The two-phase bubbly flow and boiling heat transfer in microgravity represents a substantial challenge to scientists and engineers and yet there is an urgent need to seek fundamental understanding in this area for future spacecraft design and space missions. At Washington State University, we have successfully designed, built and tested a 2.1 second drop tower with an innovation airbag deceleration system. Microgravity boiling experiments performed in our 0.6 second Drop Tower produced data flow visualizations that agree with published results and also provide some new understanding concerning flow boiling and microgravity bubble behavior. On the analytical and numerical work, the edge effects of finite divergent electrode plates on the forces experienced by bubbles were investigated. Boiling in a concentric cylinder microgravity and an electric field was numerically predicted. We also completed a feasibility study for microgravity boiling in an acoustic field.

Chung, Jacob N.↗
NASA NTRS1994

On the dynamics of a shock-bubble interaction

We present a detailed numerical study of the interaction of a weak shock wave with an isolated cylindrical gas inhomogenity. Such interactions have been studied experimentally in an attempt to elucidate the mechanisms whereby shock waves propagating through random media enhance mixing. Our study concentrates on the early phases of the interaction process which are dominated by repeated refractions of acoustic fronts at the bubble interface. Specifically, we have reproduced two of the experiments performed by Haas and Sturtevant : M(sub s) = 1.22 planar shock wave, moving through air, impinges on a cylindrical bubble which contains either helium or Refrigerant 22. These flows are modelled using the two-dimensional, compressible Euler equations for a two component fluid (air-helium or air-Refrigerant 22). Although simulations of shock wave phenomena are now fairly commonplace, they are mostly restricted to single component flows. Unfortunately, multi-component extensions of successful single component schemes often suffer from spurious oscillations which are generated at material interfaces. Here we avoid such problems by employing a novel, nonconservative shock-capturing scheme. In addition, we have utilized a sophisticated adaptive mesh refinement algorithm which enables extremely high resolution simulations to be performed relatively cheaply. Thus we have been able to reproduce numerically all the intricate mechanisms that were observed experimentally (e.g., transitions from regular to irregular refraction, cusp formation and shock wave focusing, multi-shock and Mach shock structures, jet formation, etc.), and we can now present an updated description for the dynamics of a shock-bubble interaction.

Quirk, James J.↗
NASA NTRS1995

Bubble-Free Containers For Liquids In Microgravity

Reports discuss entrainment of gas bubbles during handling of liquids in microgravity, and one report proposes containers filled with liquids in microgravity without entraining bubbles. Bubbles are troublesome in low-gravity experiments - particularly in biological experiments. Wire-mesh cage retains liquid contents without solid wall, because in microgravity, surface tension of liquid exerts sufficient confining force.

Kornfeld, Dale M.↗
NASA NTRS1996

Shape Oscillations of Gas Bubbles With Newtonian Interfacial Rheological Properties

The oscillation frequency and damping rate for small-amplitude axisymmetric shape modes of a gas bubble in an ideal liquid are obtained, in the limit when the bubble interface possesses Newtonian interfacial rheology with constant surface shear and dilatational viscosities. Such results permit the latter surface properties to be measured by analyzing experimental data on frequency shift and damping rate of specific shape modes of suspended bubbles in the presence of surfactants.

Nadim, Ali↗
NASA NTRS1998

Bubble, Drop and Particle Unit (BDPU)

This section of the Life and Microgravity Spacelab (LMS) publication includes the following articles entitled: (1) Oscillatory Thermocapillary Instability; (2) Thermocapillary Convection in Multilayer Systems; (3) Bubble and Drop Interaction with Solidification Front; (4) A Liquid Electrohydrodynamics Experiment; (5) Boiling on Small Plate Heaters under Microgravity and a Comparison with Earth Gravity; (6) Thermocapillary Migration and Interactions of Bubbles and Drops; and (7) Nonlinear Surface Tension Driven Bubble Migration

Source record↗
NASA NTRS2000

Cryoconite and Ice-bubble Microbial Ecosystems in Antarctica

During the Antarctica 2000 Expedition samples of rocks and ice bubbles entrained in ice were collected from the blue ice fields near the Moulton Escarpment of the Thiel Mountains (85S, 94W) and the Morris Moraine of the Patriot Hills (80S, 8 1 W) Ellsworth Mountains of Antarctica. Investigation of the microbiota of these cryoconite and ice bubble ecosystems are now being conducted to help refine chemical and morphological biomarkers of potential significance to Astrobiology. The Antarctica 2000 Expedition will be discussed and the preliminary results of the studies of the ice bubble and cryoconite microbial ecosystems discussed. Recent ESEM images of the Antarctic microbiota will be presented a the relevance of ice ecosystems to Astrobiology will be discussed.

Hoover, Richard B.↗