Results for “Paste” — Page 3

NASA NTRS1987

Steady flow past sudden expansions at large Reynolds number. II - Navier-Stokes solutions for the cascade expansion

The equations of motion in the steady laminar flow past a sudden expansion at large Reynolds number, R, reduce to the boundary layer equations as R tends to the freestream valve, when the longitudinal length scale of the separated eddy increases linearly and indefinitely with R. A global Newton method is presently used to obtain finite difference solutions to the steady Navier-Stokes equations up to R of 1000 for a uniform inflow past a cascade of sudden expansions. For large expansion ratio values, the eddy length increases linearly with R; for smaller values, however, where boundary layer equation solutions could not be found, the steady solutions to the Navier-Stokes equations approach the limit of an inviscid eddy in length with increasing R.

Milos, Frank S.↗

NASA NTRS1986

Statistics of the geomagnetic secular variation for the past 5Ma

A new statistical model is proposed for the geomagnetic secular variation over the past 5Ma. Unlike previous models, the model makes use of statistical characteristics of the present day geomagnetic field. The spatial power spectrum of the non-dipole field is consistent with a white source near the core-mantle boundary with Gaussian distribution. After a suitable scaling, the spherical harmonic coefficients may be regarded as statistical samples from a single giant Gaussian process; this is the model of the non-dipole field. The model can be combined with an arbitrary statistical description of the dipole and probability density functions and cumulative distribution functions can be computed for declination and inclination that would be observed at any site on Earth's surface. Global paleomagnetic data spanning the past 5Ma are used to constrain the statistics of the dipole part of the field. A simple model is found to be consistent with the available data. An advantage of specifying the model in terms of the spherical harmonic coefficients is that it is a complete statistical description of the geomagnetic field, enabling us to test specific properties for a general description. Both intensity and directional data distributions may be tested to see if they satisfy the expected model distributions.

Constable, C. G.↗

NASA NTRS1987

Simulation of separated flow past a bluff body using Navier-Stokes equations

Two-dimensional flow past a bluff body is presently simulated on the basis of an analysis that employs the incompressible, unsteady Navier-Stokes equations in terms of vorticity and stream function. The fully implicit, time-marching, alternating-direction, implicit-block Gaussian elimination used is a direct method with second-order spatial accuracy; this allows it to avoid the introduction of any artificial viscosity. Attention is given to the simulation of flow past a circular cylinder with and without symmetry, requiring the use of either the half or the full cylinder, respectively.

Ghia, K. N.↗

NASA NTRS1988

Statistics of the geomagnetic secular variation for the past 5 m.y

A new statistical model is proposed for the geomagnetic secular variation over the past 5Ma. Unlike previous models, the model makes use of statistical characteristics of the present day geomagnetic field. The spatial power spectrum of the non-dipole field is consistent with a white source near the core-mantle boundary with Gaussian distribution. After a suitable scaling, the spherical harmonic coefficients may be regarded as statistical samples from a single giant Gaussian process; this is the model of the non-dipole field. The model can be combined with an arbitrary statistical description of the dipole and probability density functions and cumulative distribution functions can be computed for declination and inclination that would be observed at any site on Earth's surface. Global paleomagnetic data spanning the past 5Ma are used to constrain the statistics of the dipole part of the field. A simple model is found to be consistent with the available data. An advantage of specifying the model in terms of the spherical harmonic coefficients is that it is a complete statistical description of the geomagnetic field, enabling us to test specific properties for a general description. Both intensity and directional data distributions may be tested to see if they satisfy the expected model distributions.

Constable, C. G.↗

NASA NTRS1989

Analysis of high-incidence separated flow past airfoils

An unsteady Navier-Stokes (NS) analysis is developed and used to carefully examine high-incidence aerodynamic separated flows past airfoils. Clustered conformal C-grids are employed for the 12 percent thick symmetric Joukowski airfoil as well as for the NACA 0012 airfoil with a sharp trailing edge. The clustering is controlled by appropriate one-dimensional stretching transformations. An attempt is made to resolve many of the dominant scales of an unsteady flow with massive separation, while maintaining the transformation metrics to be smooth and continuous in the entire flow field. A fully implicit time-marching alternating-direction implicit-block Gaussian elimination (ADI-BGE) method is employed, in which no use is made of any explicit artificial dissipation. Detailed results are obtained for massively separated, unsteady flow past symmetric Joukowski and NACA 0012 airfoils.

Chia, K. N.↗

NASA NTRS1989

Satellite cloud retrieval - Past, present, future

Satellite cloud observation is reviewed, including past accomplishments, current problems, and possible future developments. Past and current cloud retrieval algorithms are discussed, noting efforts to overcome various problems associated with cloud retrieval. The Hybrid Bispectral Threshold Method (Minnis and Harrison, 1984), the CO2 slicing algorithm (Chahine, 1974) and the ISCCEP algorithm (Rossow et al., 1985) are considered. An error analysis is presented for the determination of reference cloud fraction from Landsat TM data. The implications of the preliminary results from the First ISCCP Regional Experiment are examined and plans for future research projects are given.

Wielicki, Bruce A.↗

NASA NTRS1991

Turbulent separated flow past a backward-facing step: A critical evaluation of two-equation turbulence models

The ability of two-equation models to accurately predict separated flows is analyzed from a combined theoretical and computational standpoint. Turbulent flow past a backward facing step is chosen as a test case in an effort to resolve the variety of conflicting results that were published during the past decade concerning the performance of two-equation models. It is found that the errors in the reported predictions of the k-epsilon model have two major origins: (1) numerical problems arising from inadequate resolution, and (2) inaccurate predictions for normal Reynolds stress differences arising from the use of an isotropic eddy viscosity. Inadequacies in near wall modelling play a substantially smaller role. Detailed calculations are presented which strongly indicate the standard k-epsilon model - when modified with an independently calibrated anisotropic eddy viscosity - can yield surprisingly good predictions for the backstep problem.

Thangam, S.↗

NASA NTRS1991

Molecular dynamics computations of two dimensional supersonic rarefied gas flow past blunt bodies

This paper presents results of molecular dynamics computations of supersonic flow past a circular cylinder and past a flat plate perpendicular to a supersonic stream. The results are for Mach numbers of approximately 5 and 10, for several Knudsen numbers and several ratios of surface to free stream temperatures. A special feature of the computations is the use of relatively small numbers of particles in the molecular dynamics simulation, and an examination of the adequacy of using small numbers of particles to obtain physically useful results.

Greber, Isaac↗

NASA NTRS1992

Turbulent flow past a backward-facing step - A critical evaluation of two-equation models

The ability of two-equation models to accurately predict separated flows is analyzed from a combined theoretical and computational standpoint. Turbulent flow past a backward facing step is chosen as a test case in an effort to resolve the variety of conflicting results that were published during the past decade concerning the performance of two-equation models. It is found that the errors in the reported predictions of the k-epsilon model have two major origins: (1) numerical problems arising from inadequate resolution, and (2) inaccurate predictions for normal Reynolds stress differences arising from the use of an isotropic eddy viscosity. Inadequacies in near wall modelling play a substantially smaller role. Detailed calculations are presented which strongly indicate the standard k-epsilon model - when modified with an independently calibrated anisotropic eddy viscosity - can yield surprisingly good predictions for the backstep problem.

Thangam, S.↗

NASA NTRS1992

The possibility of life on Mars during a water-rich past

Geomorphological evidence for past liquid water on Mars implies an early, warmer, epoch. In this review we compare this early warm environment to the first Gyr of Earth's history, the time within which we know life originated. We consider the key question about early Mars from the biological standpoint. How long was liquid water present? The range of answers encompasses the time interval for the origin of life on Earth. We use studies of early life on Earth as a guide, albeit a limited one, to the possible forms of evidence for past life on Mars. Presumptive evidence for microbial life on early Earth are stromatolites, layered deposits produced by microorganisms binding and trapping sediment. A search for fossils might be fruitful at sites on Mars that contained standing bodies of water over long periods of time. The ice-covered lakes of the dry valleys of Antarctica may provide analogs to the ultimate lakes on Mars as the surface pressure fell with a concomitant decrease in surface temperatures.

Mckay, C. P.↗

NASA NTRS1990

Transition in supersonic flow past axisymmetric bodies

The paper reviews some recent work on the stability of supersonic flow past axisymmetric bodies. Results indicate that tranverse curvature effect can both be stabilizing or destabilizing depending upon the particular instability modes involved. Small nose bluntness is found to have a stabilizing influence on the flow past a cone. The relevance of these results to supersonic boundary-layer transition is brought out and comparison with the experimental data is made where possible.

Malik, M. R.↗

NASA NTRS1993

A numerical study of the effect of geometry variation, turbulence models, and dissipation on the flow past control surfaces

The steady 3D viscous flow past the ONERA M6 wing and a slender delta wing-body with trailing edge control surfaces has been computed. A cell-centered finite-volume Navier-Stokes patched zonal method has been used for the numerical simulation. Both diagonalized and LUSGS schemes have been implemented. Besides the standard nonplanar zonal interfacing techniques, a new virtual zone capability has been employed. For code validation, the transonic flow past the ONERA M5 wing is calculated for angles-of-attack of 3.06 deg and 5.06 deg and compared with the available experiments. The wing-body computational results are compared with experimental data for both trailing-edge flaps deflected. The experimental flow conditions are M subinfinity = 0.4, a turbulent Reynolds number of 5.41 million based on a mean aerodynamic chord of 25.959 inches, adiabatic wall, and angles-of-attack varying from 0 deg to 23.85 deg. The computational results are presented for the 23.85 deg angle-of-attack case. The effects of the base flow due to a model sting, the varying second and fourth order numerical dissipation, and the turbulence model are all considered.

Chaussee, Denny S.↗

NASA NTRS1940

The flow of a compressible fluid past a sphere

The flow of a compressible fluid past a sphere fixed in a uniform stream is calculated to the third order of approximation by means of the Janzen-Rayleigh method. The velocity and the pressure distribution over the surface of the sphere are computed and the terms involving the fourth power of the Mach number, neglected in Rayleigh's calculation, are shown to be of considerable importance as the local velocity of sound is approached on the sphere. The critical Mach number, that is, the value of the Mach number at which the maximum velocity of the fluid past the sphere is just equal to the local velocity of sound, is calculated for both the second and the third approximation and is found to be, respectively, Mcr=0.587 and Mcr=0.573.

Kaplan, Carl↗

NASA NTRS1952

Effect of Compressibility on the Flow past a Two-dimensional Bump

An investigation has been conducted to determine experimentally the effects of compressibility on the flow past a bump and to compare the experimentally determined results with theory. Pressure measurements and Schlieren photographs were made of the flow past two bumps having thickness-chord ratios of 0.10 and 0.30 at Mach numbers between 0.20 and 0.84

FLOW, SUBSONIC↗

NASA NTRS1952

On a solution of the nonlinear differential equation for transonic flow past a wave-shaped wall

The Prandtl-Busemann small-perturbation method is utilized to obtain the flow of a compressible fluid past an infinitely long wave-shaped wall. When the essential assumption for transonic flow (that all Mach numbers in the region of flow are nearly unity) is introduced, the expression for the velocity potential takes the form of a power series in the transonic similarity parameter. On the basis of this form of the solution, an attempt is made to solve the nonlinear differential equation for transonic flow past the wavy wall. The analysis utilized exhibits clearly the difficulties inherent in nonlinear-flow problems.

Kaplan, Carl↗

NASA NTRS1953

On transonic flow past a wave-shaped wall

This report is an extension of a previous investigation (described in NACA rep. 1069) concerned with the solution of the nonlinear differential equation for transonic flow past a wavy wall. In the present work several new notions are introduced which permit the solution of the recursion formulas arising from the method of integration in series. In addition, a novel numerical tests of convergence, applied to the power series (in transonic similarity parameter) representing the local Mach number distribution at the boundary, indicates that smooth symmetrical potential flow past the wavy wall is no longer possible once the critical value of the stream Mach number has been exceeded.

Kaplan, Carl↗

NASA NTRS1994

Hand-Controlled Brazing-Paste Dispenser

Hand control proven superior to foot control. Hand-operated switch added to hand-held brazing-alloy-paste dispenser yields improved, more consistent brazing-alloy beads. Dispenser used to apply paste between adjacent tubes in heat exchanger. Switch reliable and safe, and removed and reattached easily.

Gilbert, Jeffrey L.↗

NASA NTRS1994

An automatic 14-day paste diet feeder for animals

During a centrifuge experiment, any interruption that requires stopping the centrifuge may influence the results. Centrifuges often must be stopped for animal maintenance (food, water and waste removal), especially in cases of timed feedings. To eliminate the need for stopping the centrifuge while still providing timed feeding, an automatic paste diet feeder was developed. The feeder is based on a constant volume concept and can deliver a predetermined amount of paste diet at specified time intervals. This unit was supported by water delivery and waste collection systems. The entire system performed reliably and maintained the animals well for a continuous centrifugation experiment of 14 days.

Vasques, Marilyn↗