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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 1,027 records · Page 57
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

The production curve for agglutinates in planetary regoliths

Models for the production of agglutinates are developed that can be applied to the lunar surface or to any planetary or asteroidal body lacking an atmosphere. Models are developed using rate equations for progressively more complex situations and range from Model 1, which is a simple linear increase of agglutinate content with time, to Model 4, which includes provision for recycling of existing agglutinates and replenishment and burial of exposed soil. Model 4 has some aspects of a steady state because, depending on the rate constants, agglutinate content may be limited to an intermediate value, even for long exposure times. In an extreme case, agglutinate content may be limited to a value near zero. These models predict that agglutinates should be low in abundance in areas of thin regolith, such as the Lunokhod-2 site on the moon, and on asteroids. The models may also help explain the apparent low agglutinate abundances of lunar regolith breccias and meteorite regolith breccias.

Mckay, D. S.↗
NASA NTRS1984

Computation of viscous flow in curved ducts and comparison with experimental data

A three dimensional analysis for fully viscous subsonic internal flow is evaluated. The analysis, designated PEPSIG, solves an approximate form of the Navier-Stokes equations by an implicit spatial marching procedure. Results of calculations are presented for laminar flow through two different circular cross-sectioned 180 degree bends, and for laminar and turbulent flow through circular and square cross-sectioned 22.5 to 22.5 degree S-ducts. Quantitative comparisons with experimental data are shown for all cases. Special emphasis is placed on verifying the ability of the analysis to accurately predict the distored flow fields resulting from pressure-driven secondary flows. Previously announced in STAR as N84-13404

Towne, C. E.↗
NASA NTRS1984

Pressure-strain correlations in curved wall boundary layers

Pressure-strain correlations, which represent some part of production and dissipation of Reynolds stress in turbulent wall-bounded shear layers, have been determined for the cases of boundary layer flow past a convex, a concave and a flat wall, the latter also in the case when it follows a convex wall (relaxing flow). The Large Eddy Interaction Model utilized for prediction also permits determination of the contribution from different parts of the turbulence spectra to the correlations in different parts across the boundary layer. The relation between the anisotropic nature of the correlations and the spectra in the different flow cases provides a means of testing models for the correlations.

Hong, S. K.↗
NASA NTRS1985

Duplicating Curved Tile Surfaces for Pull Testing

Strength of adhesive bonds to fragile objects with complex shapes tested easily with vacuum chucks. In bond-strength test, contact surface of chuck pressed against matching surface of bonded tile. Vacuum line extending through fine bore in chuck creates vacuum at chuck-and-tile interface. Thus, when chuck pulled away, atmospheric pressure tends to push tile away with chuck. If adhesive resists predetermined pull exerted by chuck on tile, bond acceptable. Originally developed for vacuum chucks used on silica tiles attached to outer surface of Space Shuttle orbiter, used to custom-fabricate chuck for specific tile.

Sebenick, R. H.↗
NASA NTRS1985

Io: Precise Comparison of Voyager Spectral Curves with Laboratory Measurements

In order to derive more accurate normal reflectances of regions on Io, the near-opposition (alpha 10 deg) photometry of a set of regions on the 20 W face of the satellite, the face with the most complete near-opposition Voyager imaging coverage was analyzed. Sixty-eight regions were chosen for study, each approximately 120 km on a side, and divided into three coherent color classes: white, orange, and polar brown regions. Derived Minneart parameters, while generally consistent with previous limb darkening determinations, show that: (1) for the white regions, k rises linearly with increasing B(0), which is the trend to be expected for normal materials; (2) the white regions are slightly limb brightened (k 0.5) at low wavelengths (low values of B(0)); and (3) k appears to drop with rising B(0) for the orange regions, contrary to the trend expected for most materials. Despite similar reflectances, there is one group of orange regions with large opposition surges and a second group showing significantly lower surges, possibly indicating differences in surface texture (porosity and/or particle size).

Simonelli, D. P.↗
NASA NTRS1985

Deceleration of a supersonic flow behind a curved shock wave with isentropic precompression

Three-dimensional supersonic flows of an ideal fluid in the neighborhood of bodies formed by being cut out along the streamlines of an axisymmetric flow are investigated. The flow consists of a region of isoentropic compression and a region of vortex flow. An exact solution with variable entropy is used to describe the flow in the vortex region. In the continuous flow region an approximate solution is constructed by expanding the solution in a series in a small parameter. The effect of the shape of the excision and the vorticity of the flow on compression of the jet and and the total pressure loss coefficient is studied.

Dulov, V. G.↗
NASA NTRS1984

Computation and turbulence closure models for shear flows in rotating curved bodies

This paper is concerned with the effects of rotation and curvature on the turbulence closure model. The k-epsilon model that includes the effects of curvature has been modified to include the anisotropy in turbulence. A space-marching algorithm which solves the parabolized Navier-Stokes equations is coupled with the turbulence closure model to predict the turbulent shear flow over a rotating cylinder and inside a rotating channel. The agreement between the predictions and available data is good. The rotation and curvature effects are predicted well.

Pouagare, M.↗
NASA NTRS1983

Growth of Goertler vortices in compressible boundary layers along curved surfaces

An investigation of the growth of the three-dimensional, counter-rotating, longitudinal type vortices is considered in two-dimensional laminar compressible boundary-layer flow. The basic approximation of the disturbance equations that includes the terms due to boundary layer growth is considered and solved numerically. These terms are shown to have large local effects near the neutral stability region. The study shows that the instability of the boundary layer with respect to the three-dimensional vortices sets in at higher Goertler number as Mach number increases. Also the maximum amplitude ratio of the vortices is reduced by about 20 percent as Mach number increases from 0 to 5.

El-Hady, N. M.↗
NASA NTRS1984

Heat transfer and turbulence measurements of a film-cooled flow over a convexly curved surface

Heat transfer and hydrodynamic boundary layer measurements were made in a turbulent boundary layer on a convex surface with 13 rows of injection. Both full- and partial-coverage cases were tested for three blowing ratios: 0.2, 0.4, and 0.6. Heat transfer results are discussed in terms of Stanton number with injection air temperature equal to wall temperature. In the blown region, for both m (blowing ratio) = 0.2 and 0.4, the local response of the boundary layer is dominated by curvature, and m = 0.4 shows higher cooling effects than m = 0.2 or 0.6, as expected, based on flat-plate results. Hydrodynamic measurements with a triple-hot-wire suggest the existence of two streamwise lanes. Lanes containing injection holes are highly affected by injection and show a definite streamwise evolution. Lanes which do not contain holes are not affected much by injection and show little change in the streamwise direction.

Furuhama, K.↗
NASA NTRS1986

Fitting Polynomial Equations to Curves and Surfaces

FIT is computer program for interactively determining least-squares polynomial equations that fit user-supplied data. Finds leastsquares fits for functions of two independent variables. Interactive graphical and editing capabilities in FIT enables user to control polynomial equations to be fitted to data arising from most practical applications. FIT written in FORTRAN and COMPASS.

Arbuckle, P. D.↗
NASA NTRS1985

UBV photometry of the 1982-4 eclipse of Epsilon Aurigae: A discussion of the observed light curves

At least 29 observers in nine countries have contributed photometric measurements of Epsilon Aurigae during the recent observational campaign. The present discussion is limited to data submitted by J. L. Hopkins of the Hopkins Phoenix Observatory and S. I. Ingvarsson of the Tjornisland Astronomical Observatory. Both sources are on the UBV system, with no significant systematic differences. Combined, these two sources cover the entire eclipse, from pre-ingress up to the present (April 1985). It should be noted that this eclipse is the first to have complete photometric coverage in all three broadband filters U, B, and V.

Schmidtke, P. C.↗
NASA NTRS1985

Evolution of a curved vortex filament into a vortex ring

The deformation of a hairpin-shaped vortex filament under self-induction and in the presence of shear is studied numerically using the Biot-Savart law. It is shown that the tip region of an elongated hairpin vortex evolves into a vortex ring and that the presence of mean shear impedes the process. Evolution of a finite-thickness vortex sheet under self-induction is also investigated using the Navier-Stokes equations. The layer evolves into a hairpin vortex which in turn produces a vortex ring of high Reynolds stress content. These results indicate a mechanism for the generation of ring vortices in turbulent shear flows, and a link between the experimental and numerical observation of hairpin vortices and the observation of ring vortices in the outer regions of turbulent boundary layers.

Moin, P.↗
NASA NTRS1985

Vortex sheet modeling with higher order curved panels

A numerical technique is presented for modeling the vortex sheet with a deformable surface definition, along which a continuous vortex strength distribution in the spanwise direction is applied, so that by repeatedly modifying its shape, its true configuration is approached, in the proximity of its generating wing. Design problems requiring the inclusion of a realistic configuration of the vortex sheet are numerous. Examples discussed include: control effectiveness and stability derivatives, longitudinal stability, lateral stability, canards, propellers and helicopter rotors, and trailing vortex hazards.

Nagati, M. G.↗
NASA NTRS1985

An experimental investigation of the transverse pressure gradient associated with curved free jets in the proximity of solid boundaries

An experiment has been performed to determine the mass flow and thrust augmentation associated with the flow of a two-dimensional incompressible jet issued parallel to an adjacent offset wall. A theoretical analysis based on a linear static pressure profile across the jet exit reveals that thrust augmentation is possible only for a wall offset of less than one half of the nozzle exit width. Mass flow augmentation measurements are in reasonable agreement with the proposed theory. Augmented mass flow of over three percent is observed directly, while thrust augmentation in excess of three percent is predicted when measured values of the pressure difference across the exiting jet are supplied to the theory. Measurements of the separation cavity length are presented which complement those given by previous investigators by extending the range to small values of the ratio of the wall offset to the slot height. For large offset ratios it is found that the cavity length approaches 1.25 times the wall offset distance. The initial radius of curvature of the jet centerline is found to be substantially greater than the mean radius of curvature over the cavity length, thereby indicating that the trajectory of the jet does not follow the arc of a circle as has been previously assumed.

Lund, T. S.↗
NASA NTRS1986

Evolution of a curved vortex filament into a vortex ring

The deformation of a hairpin-shaped vortex filament under self-induction and in the presence of shear is studied numerically using the Biot-Savart law. It is shown that the tip region of an elongated hairpin vortex evolves into a vortex ring and that the presence of mean shear impedes the process. Evolution of a finite-thickness vortex sheet under self-induction is also investigated using the Navier-Stokes equations. The layer evolves into a hairpin vortex which in turn produces a vortex ring of high Reynolds stress content. These results indicate a mechanism for the generation of ring vortices in turbulent shear flows, and a link between the experimental and numerical observation of hairpin vortices and the observation of ring vortices in the outer regions of turbulent boundary layers.

Moin, P.↗