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At least 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Chaotic behavior and fluid dynamics

It is shown that while fluids are very complicated systems having many degrees of freedom, the basic mechanism underlying the observed chaotic behavior of fluid turbulence may not require the consideration of many degrees of freedom. Simple dynamical systems display erratic and chaotic behavior reminiscent of turbulence, the key to which is the 'sensitivity to initial conditions' introduced by Ruelle (1978). Simple models which are sensitive to initial data and have permitted workers to study chaotic behavior are described, with attention to the Lorenz equations, Landau's idea of a continuous transition to turbulence via an infinite cascade of bifurcations, and one-dimensional maps.

Yorke, J. A.↗
NASA NTRS1981

Alignment of fluid molecules in an EHD contact

Dichroic infrared emission spectra have been obtained from an operating elastohydrodynamic contact under conditions showing unequivocally that the molecules of the fluid are aligned under shear flow in the bulk of the fluid and that the extent of the alignment is increased by the presence of an additive in a small concentration. This work applied particularly to polyphenyl ether and to 1,1,2-trichloroethane as the additive, but similar results have been obtained with polycyclohexyls and the same additive. The observation of two separate glass transitions for the polycyclohexyl solution is an indication of the occurrence of a phase separation in the Hertzian inlet zone. A model has been developed to explain the effect of these phenomena and their relation to traction.

Lauer, J. L.↗
NASA NTRS1982

Low-gravity fluid flows

The behavior of fluids in micro-gravity conditions is examined, with particular regard to applications in the growth of single crystals. The effects of gravity on fluid behavior are reviewed, and the advent of Shuttle flights are noted to offer extended time for experimentation and processing in a null-gravity environment, with accelerations resulting solely from maneuvering rockets. Buoyancy driven flows are considered for the cases stable-, unstable-, and mixed-mode convection. Further discussion is presented on g-jitter, surface-tension gradient, thermoacoustic, and phase-change convection. All the flows are present in both gravity and null gravity conditions, although the effects of buoyancy and g-jitter convection usually overshadow the other effects while in a gravity field. Further work is recommended on critical-state and sedimentation processes in microgravity conditions.

Ostrach, S.↗
NASA NTRS1981

International Conference on Numerical Methods in Fluid Dynamics, 7th, Stanford University, Stanford and Moffett Field, CA, June 23-27, 1980, Proceedings

Topics discussed include polygon transformations in fluid mechanics, computation of three-dimensional horseshoe vortex flow using the Navier-Stokes equations, an improved surface velocity method for transonic finite-volume solutions, transonic flow calculations with higher order finite elements, the numerical calculation of transonic axial turbomachinery flows, and the simultaneous solutions of inviscid flow and boundary layer at transonic speeds. Also considered are analytical solutions for the reflection of unsteady shock waves and relevant numerical tests, reformulation of the method of characteristics for multidimensional flows, direct numerical simulations of turbulent shear flows, the stability and separation of freely interacting boundary layers, computational models of convective motions at fluid interfaces, viscous transonic flow over airfoils, and mixed spectral/finite difference approximations for slightly viscous flows.

Reynolds, W. C.↗
NASA NTRS1982

Computational fluid dynamics - The coming revolution

The development of aerodynamic theory is traced from the days of Aristotle to the present, with the next stage in computational fluid dynamics dependent on superspeed computers for flow calculations. Additional attention is given to the history of numerical methods inherent in writing computer codes applicable to viscous and inviscid analyses for complex configurations. The advent of the superconducting Josephson junction is noted to place configurational demands on computer design to avoid limitations imposed by the speed of light, and a Japanese projection of a computer capable of several hundred billion operations/sec is mentioned. The NASA Numerical Aerodynamic Simulator is described, showing capabilities of a billion operations/sec with a memory of 240 million words using existing technology. Near-term advances in fluid dynamics are discussed.

Graves, R. A., Jr.↗
NASA NTRS1982

Evidence for the three-stage cooling history of olivine-porphyritic fluid droplet chondrules

A three-stage model for the cooling of olivine-porphyritic fluid droplet chondrules found in ordinary chondrites is proposed, in light of an experimental examination of three haplochondritic melts to determine thermal parameters in a pre-accretionary chondrule environment. The model encompasses: (1) initial continuous cooling from at least liquidus temperatures, at 300-4000 C/hour, to about 1300 C, over approximately 5-60 min; (2) interruption of the initial cooling by a short-duration isothermal event at about 1300 C; and (3) quenching. This thermal model, in which the entire history of fluid droplet chondrules is only a brief process in the early history of the solar system, suggests a specific and restricted physical origin for chondrules which is not likely to have been achieved by such repetitive, small-scale events as planetary surface impact splattering or volcanism. A single, large-scale event is postulated.

Planner, H. N.↗
NASA NTRS1982

Numerical solutions for the spin-up of a stratified fluid

The model of Warn-Varnas et al. (1978) is used to numerically examine the spin-up flow of a thermally stratified fluid in a cylinder with an insulating side wall, and comparison of the results with the laser-Doppler measurements of Lee (1975) shows excellent agreement. It is shown that flow gradients are created in the interior of the fluid during the meridional circulation spin-up phase, and that the azimuthal flow decayed faster than has been predicted by Wallin (1969). It is established that viscous diffusion in the interior, arising from the interior-flow gradients, is the cause of the discrepancy with Wallin's theory.

Hyun, J. M.↗
NASA NTRS1982

A mathematical model of post-instability in fluid mechanics

Postinstability of fluids is eliminated in numerical models by introducing multivalued velocity fields after discarding the principle of impenetrability. Smooth functions are shown to be incapable of keeping the derivatives from going towards infinity when iterating solutions for the governing equations such as those defined by Navier-Stokes. Enlarging the class of functions is shown to be necessary to eliminate the appearance of imaginary characteristic roots in the systems of arbitrary partial differential equations, a condition which leads to physically impossible motions. The enlarging is demonstrated to be achievable by allowing several individual particles with different velocities to appear at the same point of space, and the subsequent multivaluedness of the solutions is purely a mathematical concern, rather than one of actual physical existence. Applications are provided for an inviscid fluid and for turbulence.

Zak, M. A.↗
NASA NTRS1982

Cryogenic fluid transfer - orbital transfer vehicle

Fluid transfer requirements are presented for the orbital transfer vehicle (OTV) issues such as OTV configuration, hardware design and size are taken into consideration. Tank chilldown, tank fill and thermodynamic properties are all evaluated in relationship to fluid transfer needs.

Hastings, L. J.↗
NASA NTRS1982

Solution of axisymmetric fluid structure interaction problems with NASTRAN

The solution of axisymmetric acoustic fluid structure interaction problems, employing the NASTRAN computer program is presented. A previously developed 3-D Cartesian Coordinates pressure element formulation is adapted especially for axisymmetric elements. Analogous to the 3-D Cartesian Coordinate predecessor, the fluid portion of the problem is modeled with finite elements wherein one of the displacement components serves as a dummy variable for the pressure unknowns. Two alternatives for implementation of the analogy are presented: (1) an approximate method by which dummy values of G, and nu are used to approximately invoke the analogy wherein the accuracy of the approximation is made as close as desired to the proper analogy within an arbitrary small parameter epsiton; (2) an exact method whereby the NASTRAN FORTRAN coding is slightly changed to invoke the analogy exactly. Comparison of the finite element solution to the exact solution to the same problem is given.

Kalinowski, A. J.↗
NASA NTRS1982

Data use investigation for the magnetic field satellite (MAGSAT) mission: Geomagnetic field forecasting and fluid dynamics of the core

MAGSAT data were used to construct a variety of spherical harmonic models of the main geomagnetic field emanating from Earth's liquid core at poch 1980. These models were used to: (1) accurately determine the radius of Earth's core by a magnetic method, (2) calculate estimates, of the long-term ange of variation of geomagnetic Gauss coefficients; (3) establish a preferred truncation level for current spherical harmonic models of the main geomagnetic field from the core; (4) evaluate a method for taking account of electrical conduction in the mantle when the magnetic field is downward continued to the core-mantle boundary; and (5) establish that upwelling and downwelling of fluid motion at the top of the core is probably detectable, observationally. A fluid dynamics forecast model was not produced because of insufficient data.

Benton, E. R.↗
NASA NTRS1983

Traction calculations and design data for two traction fluids

The rheological properties of the fluid under these certain conditions which precludes the use of most of the conventional instruments for steady state measurement were studied. The only suitable type of instrument is a disk machine where most of the conditions are the same of similar to those in traction drives. From the resulting traction tests, certain models are inferred. To the designer of traction drives, the traction behavior of the fluid under the severe conditions is of utmost importance because of the direct influence that it has on the efficiency, size, and life of a given drive.

Tevaarwerk, J. L.↗
NASA NTRS1983

Dual laser optical system and method for studying fluid flow

A dual laser optical system and method is disclosed for visualization of phenomena in transport substances which induce refractive index gradients such as fluid flow and pressure and temperature gradients in fluids and gases. Two images representing mutually perpendicular components of refractive index gradients may be viewed simultaneously on screen. Two lasers having wave lengths in the visible range but separated by about 1000 angstroms are utilized to provide beams which are collimated into a beam containing components of the different wave lengths. The collimated beam is passed through a test volume of the transparent substance. The collimated beam is then separated into components of the different wave lengths and focused onto a pair of knife edges arranged mutually perpendicular to produce and project images onto the screen.

Owen, R. B.↗
NASA NTRS1982

Investigation of the effects of initial fluid film profile on pumping ring operation

The effect of the initial fluid film profile on the pumping capacity of a pumping ring shaft seal has been investigated numerically. Linear, concave, convex and compound film shapes were considered. It was found that initial film shape has a pronounced effect on both the amount of fluid pumped and on the character of the flow pattern and pressure distribution within the film.

Smith, P. J.↗
NASA NTRS1982

Perfect fluids in the Einstein-Cartan theory

It is pointed out that whereas most of the discussion of the Einstein-Cartan (EC) theory involves the relationship between gravitation and elementary particles, it is possible that the theory, if correct, may be important in certain extreme astrophysical and cosmological problems. The latter would include something like the collapse of a spinning star or an early universe with spin. A set of equations that describe a macroscopic perfect fluid in the EC theory is derived and examined. The equations are derived starting from the fundamental variational principle for a perfect fluid in general relativity. A brief review of the study by Ray (1972) is included, and the results for the EC theory are presented.

Ray, J. R.↗
NASA NTRS1983

Fluid mechanics in crystal growth - The 1982 Freeman scholar lecture

An attempt is made to unify the current state of knowledge in crystal growth techniques and fluid mechanics. After identifying important fluid dynamic problems for such representative crystal growth processes as closed tube vapor transport, open reactor vapor deposition, and the Czochralski and floating zone melt growth techniques, research results obtained to date are presented. It is noted that the major effort to date has been directed to the description of the nature and extent of bulk transport under realistic conditions, where bulk flow determines the heat and solute transport which strongly influence the temperature and concentration fields in the vicinity of the growth interface. Proper treatment of near field, or interface, problems cannot be given until the far field, or global flow, involved in a given crystal growth technique has been adequately described.

Ostrach, S.↗
NASA NTRS1982

Thresholds for the onset of fluid and magnetofluid turbulence

Linear stability calculations conducted in plasma physics are based on the theory of hydrodynamic stability of neutral fluids. The present investigation is concerned with the validity of procedures based on linear stability analysis in six much-studied situations. All have the property that the fluid goes from laminar to turbulent at critical values of some dimensionless number, such as the Reynolds number or the Rayleigh number. The question is, at what threshold values of the dimensionless number do the unstable motions set in, and can these thresholds be predicted by a linear analysis of the stability of the laminar state as the threshold is approached from the stable side. In three cases linear stability analysis clearly seems to fail. These cases include Plane Poiseuille Flow, Plane Couette Flow, and Cylindrical Pipe Flow (Hagen-Poiseuille Flow). Situations in which predictions provided by linear stability analysis are correct are related to Rotating Couette Flow, Thermally-Driven Convection, and Instability of Laminar Boundary Layers.

Montgomery, D.↗
NASA NTRS1983

Spinning fluids in the Einstein-Cartan theory

An Eulerian variational principle for a spinning fluid in the Einstein-Cartan metric-torsion theory is presented. The variational principle yields the complete set of field equations for the system. The symmetric energy-momentum tensor is a sum of a perfect-fluid term and a spin term.

Ray, J. R.↗