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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 1,261 records · Page 70
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Ultrasonic testing of plates containing edge cracks

The stress wave factor (SWF) signal is utilized for the nondestructive evaluation of plates containing perpendicular edge cracks. The effects of the existence lateral location and depth of the crack on the magnitude spectra of individual reflections in the SWF signal are studied. If the reflections in the SWF signal are not overlapped the short time Fourier analysis is applied. If the reflections are overlapped the short time homomorphic analysis (cepstrum analysis) is applied. Several reflections which have average resonant frequencies approximately at 0.9, 1.3, and 1.7 MHz are analyzed. It is observed that the magnitude ratios evaluated at average resonant frequencies decrease more with increasing d/h if the crack is located between the transducers, where h is plate thickness and d is crack depth. Moreover, for the plates, crack geometries, reflections, and frequencies considered, the average decibel drop depends mainly on the dimensionless parameter d/h and it is approximately -1 dB per 0.07 d/h. Changes in the average resonant frequencies of the magnitude spectra are also observed due to changes in the location of the crack.

Williams, J. H., Jr.↗
NASA NTRS1985

On the application of a hairpin vortex model of wall turbulence to trailing edge noise prediction

The goal is to develop a technique via a hairpin vortex model of the turbulent boundary layer, which would lead to the estimation of the aerodynamic input for use in trailing edge noise prediction theories. The work described represents an initial step in reaching this goal. The hairpin vortex is considered as the underlying structure of the wall turbulence and the turbulent boundary layer is viewed as an ensemble of typical hairpin vortices of different sizes. A synthesis technique is examined which links the mean flow and various turbulence quantities via these typical vortices. The distribution of turbulence quantities among vortices of different scales follows directly from the probability distribution needed to give the measured mean flow vorticity. The main features of individual representative hairpin vortices are discussed in detail and a preliminary assessment of the synthesis approach is made.

Liu, N. S.↗
NASA NTRS1985

Evidence for a dynamical halo around the edge-on galaxy NGC 4631

Radio continuum observations at five frequencies between 327 MHz and 10.7 GHz of the edge on galaxy NGC 4631 confirm the prediction concerning the frequency dependence of the halo extent and the spatial variations of the radio spectral indices in the dynamical halo model made by Lerche and Schlickeiser. The measurements are presented, and a detailed comparison with theoretical predictions is made.

Lerche, I.↗
NASA NTRS1984

Airfoil trailing edge flow measurements and comparison with theory, incorporating open wind tunnel corrections

Trailing edge data for boundary layer-near wake thickness parameters are given for airfoils and flat plates. Reynolds number effects are examined as a function of model size, velocity and boundary layer tripping. These data expand that presented previously by the authors particularly for airfoil non-zero angles of attack. Comparisons are made here with boundary layer calculations using potential flow modeling and a well documented two-dimensional finite-difference method for laminar and turbulent boundary layers. Open wind tunnel corrections to angle of attack and camber are developed and are incorporated in the potential flow modeling to assure correct comparisons for non-zero angles of attack. It was found that although the open tunnel flow turbulence affected boundary layer transition for the higher velocities the theory successfully 'brackets' the data. Comparisons demonstrate the degree of accuracy one might expect for the prediction of boundary layer thickness parameters when given only geometry and nominal flow conditions as input to boundary layer codes.

Brooks, T. F.↗
NASA NTRS1983

Determination of interlaminar fracture toughness and fracture mode dependence of composites using the edge delamination test

Edge delamination testing has been conducted in order to determine the mixed mode interlaminar fracture toughness of unnotched (+, -35/0/90)s and (0/+, -35/90)s laminates with graphite fibers and epoxy matrices, with or without elastomer additives. Although the two stacking sequences were chosen so that the total strain energy release rates were equal, the percentages of crack opening and shear mode energy release rates were found to vary widely between the layups. Plots of interlaminar fracture toughness as a function of crack opening energy release rate percentage have been drawn to generate delamination failure criteria which reflect the observed fracture mode dependence.

Obrien, T. K.↗
NASA NTRS1984

Sharp edges in solar microwave spectra - Neutral current sheets or cyclotron lines?

Two solar active regions have been mapped using the VLA at three closely spaced frequencies (4496, 4716, and 4996 MHz) in an attempt to determine the origin of the steep spectra (index gamma equal to about -5 to -8) sometimes observed with large single telescopes. One of the regions observed indeed shows an anomalously large slope (gamma equal to about -6) compared to the usual (gamma equal to about -2 to -2.5). The other region shows a similar slope (gamma equal to about -5) but with a larger range of statistical error. Two possible explanations for such steep edges in solar spectra are (1) transmission effects of neutral current sheets, and (2) the appearance of cyclotron lines. The internal evidence of the microwave maps and simultaneous optical observations favor an explanation in terms of cyclotron lines.

Schmahl, E. J.↗
NASA NTRS1984

Analysis of airfoil leading-edge separation bubbles

A local inviscid-viscous interaction technique was developed for the analysis of low speed airfoil leading edge transitional separation bubbles. In this analysis an inverse boundary layer finite difference analysis is solved iteratively with a Cauchy integral representation of the inviscid flow which is assumed to be a linear perturbation to a known global viscous airfoil analysis. Favorable comparisons with data indicate the overall validity of the present localized interaction approach. In addition numerical tests were performed to test the sensitivity of the computed results to the mesh size, limits on the Cauchy integral, and the location of the transition region.

Vatsa, V. N.↗
NASA NTRS1984

Approximate analysis for resonance of an incompressible shear layer plus edges

A method for approximately analyzing the feedback between downstream and upstream edges in incompressible shear flow is described. The shear flow is modeled by a vortex sheet. Equations for resonance eigenvalues are derived. After the reduction of growth rate by finite shear layer thickness is allowed for, agreement is found between calculated resonances and those that have been observed experimentally.

Durbin, P. A.↗
NASA NTRS1985

A theory for the core of a three-dimensional leading-edge vortex

A theory is presented for the flow in the core of a separation-induced leading-edge vortex. The theory is based on matching inner and outer representations of the vortex. The inner representation models continuously distributed vorticity and includes an asymptotic viscous subcore. The outer representation models concentrated spiral sheets of vorticity and is fully three dimensional. A parameter is identified which closely tracks the vortex breakdown stability boundary for delta, arrow, and diamond wings.

Luckring, J. M.↗
NASA NTRS1985

An attached flow design of a noninterfering leading edge extension to a thick delta wing

The analytical procedure presented for leading edge extension (LEE) determination, in keeping with such design criteria as noninterference at the wing design point, is applied to thick delta wings. The LEE device thus defined is to be mounted on a wing along a dividing stream surface that is associated with an attached flow design lift coefficient greater than zero. The delta wing in question is of twisted and cambered type. It is demonstrated that span reductions for the candidate LEEs has the most detrimental effect on overall aerodynamic efficiency, irrespective of area or shape.

Ghaffari, F.↗
NASA NTRS1985

Wavy edges suggest moonlet in Encke's gap

Voyager images have revealed radial undulations of the inner and outer edges of the 325 km wide Encke gap in Saturn's A ring. These waves are present at some, but not all, longitudes. Their locations and wavelengths provide strong indirect evidence for the presence of at least one dominant moonlet of about 10 km radius orbiting near the center of the gap. Implications for 'shepherding' theory are discussed.

Cuzzi, J. N.↗
NASA NTRS1985

A comparison of finite-difference and finite-element methods for calculating free edge stresses in composites

It is pointed out that edge delamination is a serious failure mechanism for laminated composite materials. Various numerical methods have been utilized in attempts to calculate the interlaminar stress components which precede delamination in a laminate. There are, however, discrepancies regarding the results provided by different methods, taking into account a finite-difference procedure, a perturbation procedure, and finite element approaches. The present investigation has the objective to assess the capacity of a finite difference method to predict the character and magnitude of the interlaminar stress distributions near an interface corner. A second purpose of the investigation is to determine if predictions by finite element method in-plane, interlaminar stress components near an interface corner represent actual laminate behavior.

Bauld, N. R., Jr.↗
NASA NTRS1985

Massive separation and dynamic stall on a cusped trailing-edge airfoil

The cross-over from a predominantly attached two-dimensional flow to the bluff body form of separation is modeled via the interacting boundary layer approximation. The initial breakdown of the predominantly attached flow on a cusped trailing edge airfoil is examined using the Hilbert integral form of the unsteady interacting boundary layer equations. In addition, an interacting boundary layer technique is developed for calculating bluff body separation. This new model eliminates the severe scaling problems associated with bluff body separation through the use of a realistic inviscid eddy model, based on the infinite eddy Kirchhoff free-streamline description of separation. Brief consideration is given to the cross-over from bluff body separation to a predominantly attached flow, the extension to finite eddies and cascade flows, and the possible coupling with full, or parabolized, Navier-Stokes calculations.

Rothmayer, A. P.↗
NASA NTRS1986

Hermetic Edge Seals for Photovoltaic Modules

Corrosive atmospheric agents excluded to prolong cell life. Combination of two sealing techniques makes possible to protect solar cells from water vapor, oxygen, and other corrosive atmospheric constituents. Using three-step process, glass-to-metal hermetic seal formed around edge of solar-cell module. Elastomer seals used previously not as effective because they are permeable to water vapor and atmospheric gases.

Nowlan, M. J.↗
NASA NTRS1986

Faster Edge-Define Silicon-Ribbon Growth

End-cooling allows faster growth and yields single-crystal ribbons. Improvement in edge-defined film-fed process for growing silicon ribbons increases speed of growth and improves quality of silicon product. Also produces silicon sheets, webs, or boules. Cold shoes cool melt at ends of emerging sheet. Since solidification at ends now occurs before end menisci reach maximum height, ribbon drawn substantially faster.

Richter, R.↗
NASA NTRS1986

Apparatus for edge etching of semiconductor wafers

A device for use in the production of semiconductors, characterized by etching in a rapidly rotating etching bath is described. The fast rotation causes the surface of the etching bath to assume the form of a paraboloid of revolution, so that the semiconductor wafer adjusted at a given height above the resting bath surface is only attacked by etchant at the edges.

Casajus, A.↗
NASA NTRS1986

Leading-edge vortex research: Some nonplanar concepts and current challenges

Some background information is provided for the Vortex Flow Aerodynamics Conference and that current slender wing airplanes do not use variable leading edge geometry to improve transonic drag polar is shown. Highlights of some of the initial studies combining wing camber, or flaps, with vortex flow are presented. Current vortex flap studies were reviewed to show that there is a large subsonic data base and that transonic and supersonic generic studies have begun. There is a need for validated flow field solvers to calculate vortex/shock interactions at transonic and supersonic speeds. Many important research opportunities exist for fundamental vortex flow investigations and for designing advanced fighter concepts.

Campbell, J. F.↗
NASA NTRS1986

An Euler aerodynamic method for leading-edge vortex flow simulation

The current capabilities and the future plans for a three dimensional Euler Aerodynamic Method are described. The basic solution algorithm is based on the finite volume, Runge-Kutta pseudo-time-stepping scheme of FLO-57. Several modifications to improve accuracy and computational efficiency were incorporated and others are being investigated. The computer code is used to analyze a cropped delta wing at 0.6 Mach number and an arrow wing at 0.85 Mach number. Computed aerodynamic parameters are compared with experimental data. In all cases, the configuration is impulsively started and no Kutta condition is applied at sharp edges. The results indicate that with additional development and validation, the present method will be a useful tool for engineering analysis of high speed aircraft.

Raj, P.↗