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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 757 records · Page 42
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Flux vector splitting of the inviscid gasdynamic equations with application to finite-difference methods

The conservation-law form of the inviscid gasdynamic equations has the remarkable property that the nonlinear flux vectors are homogeneous functions of degree one. This property readily permits the splitting of flux vectors into subvectors by similarity transformations so that each subvector has associated with it a specified eigenvalue spectrum. As a consequence of flux vector splitting, new explicit and implicit dissipative finite-difference schemes are developed for first-order hyperbolic systems of equations. Appropriate one-sided spatial differences for each split flux vector are used throughout the computational field even if the flow is locally subsonic. The results of some preliminary numerical computations are included.

Steger, J. L.↗
NASA NTRS1981

Stable boundary approximations for a class of implicit schemes for the one-dimensional inviscid equations of gas dynamics

The applicability to practical calculations of recent theoretical developments in the stability analysis of difference approximations for initial-boundary-value problems of the hyperbolic type. For the numerical experiments, select the one-dimensional inviscid gas-dynamic equations in conservation-law form is selected. A class of implicit schemes based on linear multistep methods for ordinary differential equations is chosen and the use of space or space-time extrapolations as implicit or explicit boundary schemes is emphasized. Some numerical examples with various inflow-outflow conditions highlight the commonly discussed issues: explicit versus implicit boundary schemes, unconditionally stable schemes, and underspecification or overspecification of boundary conditions.

Yee, H. C.↗
NASA NTRS1981

Interplanetary trajectory optimization

A procedure for minimizing total impulsive Delta-V for constrained multiple-flyby trajectories, which was originally developed for application to satellite tours, has been modified for application to interplanetary trajectories. The modification includes adding to the cost function the Delta-V required to escape from a parking orbit about the launch planet and the Delta-V required for insertion into orbit about the arrival planet. The hyperbolic excess velocity vector with respect to the launch planet and the launch date have been added to the set of independent variables for the optimization. Each trajectory originates at departure from the parking orbit rather than at a fixed position in space, as is the case for the satellite tour application. The multi-conic trajectory propagation techniques and the Newton optimization algorithm of the original method have been retained. Examples of the application of this new method are given for several types of Galileo interplanetary trajectory options, including Mars powered flyby, broken plane, VEGA, and Delta VEGA trajectories.

Damario, L. A.↗
NASA NTRS1981

Secondary and compound concentrators for parabolic dish solar thermal power systems

A secondary optical element may be added to a parabolic dish solar concentrator to increase the geometric concentration ratio attainable at a given intercept factor. This secondary may be a Fresnel lens or a mirror, such as a compound elliptic concentrator or a hyperbolic trumpet. At a fixed intercept factor, higher overall geometric concentration may be obtainable with a long focal length primary and a suitable secondary matched to it. Use of a secondary to increase the geometric concentration ratio is more likely to e worthwhile if the receiver temperature is high and if errors in the primary are large. Folding the optical path with a secondary may reduce cost by locating the receiver and power conversion equipment closer to the ground and by eliminating the heavy structure needed to support this equipment at the primary focus. Promising folded-path configurations include the Ritchey-Chretien and perhaps some three element geometries. Folding the optical path may be most useful in systems that provide process heat.

Jaffe, L. D.↗
NASA NTRS1982

Prediction of sound radiation from different practical jet engine inlets

The computer codes necessary for this study were developed and checked against exact solutions generated by the point source method using the NASA Lewis QCSEE inlet geometry. These computer codes were used to predict the acoustic properties of the following five inlet configurations: the NASA Langley Bellmouth, the NASA Lewis JT15D-1 Ground Test Nacelle, and three finite hyperbolic inlets of 50, 70 and 90 degrees. Thirty-five computer runs were done for the NASA Langley Bellmouth. For each of these computer runs, the reflection coefficient at the duct exit plane was calculated as was the far field radiation pattern. These results are presented in both graphical and tabular form with many of the results cross plotted so that trends in the results verses cut-off ratio (wave number) and tangential mode number may be easily identified.

Zinn, B. T.↗
NASA NTRS1982

LORAN-C, an overview

LORAN-C a highly accurate radio navigation positioning system which operates at an assigned frequency of 10 kHz, and provides phase-coded pulses to develop hyperbolic time-difference lines-of-position (LOP's) was evaluated. LORAN-C provides precise time and time interval to within plus or minus 5 microseconds of UTC. The steps taken to plan, install, operate, and maintain the LORAN-C system up to the year 2000 are discussed. Topics included in the discussion were: theory of operation, timing, chain lanning, group repetition interval, coding delay versus emission delay, chain calibration, chart verification, system accuracy, signal reliability, and future developments.

Thrall, W. J.↗
NASA NTRS1982

On the application and extension of Harten's high resolution scheme

Extensions of a second order high resolution explicit method for the numerical computation of weak solutions of one dimensonal hyperbolic conservation laws are discussed. The main objectives were (1) to examine the shock resoluton of Harten's method for a two dimensional shock reflection problem, (2) to study the use of a high resolution scheme as a post-processor to an approximate steady state solution, and (3) to construct an implicit in the delta-form using Harten's scheme for the explicit operator and a simplified iteration matrix for the implicit operator.

Yee, H. C.↗
NASA NTRS1982

Calculation of the flow field including boundary layer effects for supersonic mixed compression inlets at angles of attack

The flow field in supersonic mixed compression aircraft inlets at angle of attack is calculated. A zonal modeling technique is employed to obtain the solution which divides the flow field into different computational regions. The computational regions consist of a supersonic core flow, boundary layer flows adjacent to both the forebody/centerbody and cowl contours, and flow in the shock wave boundary layer interaction regions. The zonal modeling analysis is described and some computational results are presented. The governing equations for the supersonic core flow form a hyperbolic system of partial differential equations. The equations for the characteristic surfaces and the compatibility equations applicable along these surfaces are derived. The characteristic surfaces are the stream surfaces, which are surfaces composed of streamlines, and the wave surfaces, which are surfaces tangent to a Mach conoid. The compatibility equations are expressed as directional derivatives along streamlines and bicharacteristics, which are the lines of tangency between a wave surface and a Mach conoid.

Vadyak, J.↗
NASA NTRS1982

Multidomain approach for calculating compressible flows

A multidomain approach for calculating compressible flows by using unsteady or pseudo-unsteady methods is presented. This approach is based on a general technique of connecting together two domains in which hyperbolic systems (that may differ) are solved with the aid of compatibility relations associated with these systems. Some examples of this approach's application to calculating transonic flows in ideal fluids are shown, particularly the adjustment of shock waves. The approach is then applied to treating a shock/boundary layer interaction problem in a transonic channel.

Cambier, L.↗
NASA NTRS1981

Secondary concentrators for parabolic dish solar thermal power systems

A variety of different concepts are currently being studied with the objective to lower the cost of parabolic mirrors and to provide alternatives. One of the considered approaches involves the use of compound concentrators. A compound solar concentrator is a concentrator in which the sunlight is reflected or refracted more than once. It consists of a primary mirror or lens, whose aperture determines the amount of sunlight gathered, and a smaller secondary mirror or lens. Additional small optical elements may also be incorporated. The possibilities and problems regarding a use of compound concentrators in parabolic dish systems are discussed. Attention is given to concentrating secondary lenses, secondary imaging and concentrating mirrors, conical secondary mirrors, compound elliptic secondary concentrating mirrors, and hyperbolic trumpet secondary concentrating mirrors.

Jaffe, L. D.↗
NASA NTRS1981

Fresnel zone structure in planetary occultations

The structures of the Fresnel zones of an occulting body with a substantial atmosphere are analyzed. The first Fresnel zone is defined as the set of all contiguous points connected to the transmitter and receiver via paths with a combined length within one half wavelength of the stationary value, and calculated by the application of the Huygens-Fresnel principle to a wave front frozen in time as it traverses the region of interest, taking into account wave front curvature of waves undergoing refraction. Calculations of the Fresnel zones of a planet determined by the meeting of wave fronts represented as tori reveal that the zone along the propagation path traversing the nearest portion of the limb to the transmitter has a shape similar to an ellipse, while that of the far zone resembles the letter X. The phase delay along the farside path is found to be a stationary point rather than a minimum, since delay is distributed in the form of a hyperbolic paraboloid near the ray and in the form of a torus intersection for greater separations. Examples are presented for S band propagation deep in the atmospheres of Venus and Jupiter.

Croft, T. A.↗
NASA NTRS1981

Surface geometry of circular cut spiral bevel gears

An analysis of the surface geometry of spiral bevel gears formed by a circular cutter is presented. The emphasis is upon determining the tooth surface principal radii of curvature of crown (flat) gears. Specific results are presented for involute, straight, and hyperbolic cutter profiles. It is shown that the geometry of circular cut spiral bevel gears is somewhat simpler than a theoretical logarithmic spiral bevel gear.

Huston, R. L.↗
NASA NTRS1982

Mode characteristics of nonplanar double-heterojunction and large-optical-cavity laser structures

Mode behavior of nonplanar double-heterojunction (DH) and large-optical-cavity (LOC) lasers is investigated using the effective index method to model the lateral field distribution. The thickness variations of various layers for the devices discussed are correlated with the growth characteristics of liquid-phase epitaxy over topographical features (channels, mesas) etched into the substrate. The effective dielectric profiles of constricted double-heterojunction (CDH)-LOC lasers show a strong influence on transverse mode operation: the fundamental transverse mode (i.e., in the plane perpendicular to the junction) may be laterally index-guided, while the first (high)-order mode is laterally index-antiguided. The analytical model developed uses a smoothly varying hyperbolic cosine distribution to characterize lateral index variations. The waveguide model is applied to several lasers to illustrate conditions necessary to convert leaky modes to trapped ones via the active-region gain distribution. Theoretical radiation patterns are calculated using model parameters, and matched to an experimental far-field pattern.

Butler, J. K.↗
NASA NTRS1982

An efficient full potential implicit method based on characteristics for analysis of supersonic flows

A nonlinear aerodynamic prediction technique based on the full potential equation in conservation form has been developed for the treatment of supersonic flows. The method uses the theory of characteristic signal propagation to accurately simulate the flow structure, which includes shock waves and mixed elliptic-hyperbolic crossflow. An implicit approximate factorization scheme is employed to solve the finite-differenced equation. The necessary body-fitted grid system in every marching plane is generated numerically, using an elliptic grid solver. Results are shown for conical and nonconical wing-body combinations and compared with experimental data and Euler calculations. The method demonstrates an enormous savings in execution time and memory requirements over Euler methods.

Shankar, V.↗
NASA NTRS1982

Two dimensional stagnation point flow of a dusty gas near an oscillating plate

Necessary improvements to a paper on the flow of a dusty gas by Datta and Mishra (1980) are presented. Particular attention is given to the importance of particle phase compressibility and the hyperbolic nature of the particle momentum conservation equation which prohibits downstream (wall) boundary conditions for the solid phase. Fundamental differences between particulate and ordinary flow boundary layers are discussed, and the correct conservation equations are written.

Fernandez De La Mora, J.↗
NASA NTRS1982

The path and surviving tail of a comet that fell into the sun

A satisfactory orbital solution for Comet Howard-Koomen-Michels 1979 XI is found on the assumption that the comet's line of apsides coincided with that of the Kreutz sungrazing comet group. The derived perihelion distance then shows that this is the first known case of a comet falling into the sun. A dust tail that survived the comet is studied as a particle flow phenomenon controlled by no force other than solar gravity and solar radiation pressure. The tail's outline is interpreted in terms of an onset of dust production, a peak repulsive force on the particles, and a circumsolar dustfree zone due to particle sublimation. It is shown that the surviving debris consisted mostly of absorbing, submicron size particles in hyperbolic trajectories convex to the sun and curving toward the earth. The tail width may be a product of the interaction of charged dust in the tail with a complicated structure of the coronal magnetic field.

Sekanina, Z.↗
NASA NTRS1982

Aerocapture - Guidance, navigation, and control

Aerocapture is a concept for inserting a spacecraft into orbit about a target planet. The energy required for orbit insertion is obtained from natural resources present at or near the target body, thereby reducing the amount of propellant which must be carried onboard. Specifically, the transfer from a hyperbolic flyby trajectory to a desired bound orbit is effected by aerodynamic lift and drag forces acting on the spacecraft during controlled flight through the atmosphere of either the target planet or a nearby satellite. A survey is provided of the trajectory guidance, navigation, and control aspects of aerocapture, and a summary is given of the results of a number of preliminary studies concerning certain of these aspects. The investigation has additional significance in connection with the current interest in aeroassisted orbital transfer vehicles, which may be used in conjunction with the Space Shuttle.

Mease, K. D.↗
NASA NTRS1982

Analysis of aerothermodynamic environment of a Titan aerocapture vehicle

The feasibility of an aerocapture vehicle mission has been emphasized recently for inner and outer planetary missions. Aerocapture involves a system concept which utilizes aerodynamic drag to acquire the velocity reduction necessary to obtain a closed planetary orbit from a hyperbolic flyby trajectory. It has been proposed to use the atmosphere of Titan for braking into a Saturn orbit. This approach for a Saturn orbital mission is expected to cut the interplanetary cruise travel time to Saturn from 8 to 3.5 years. In connection with the preparation of such a mission, it will be necessary to provide a complete analysis of the aerodynamic environment of the Titan aerocapture vehicle. The main objective of the present investigation is, therefore, to determine the extent of convective and radiative heating for the aerocapture vehicle under different entry conditions. This can be essentially accomplished by assessing the heating rates in the stagnation and windward regions of an equivalent body.

Tiwari, S. N.↗