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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 577 records · Page 32

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NASA NTRS1973

Turbulence in electrostatic ion-acoustic shocks

Three types of collisionless electrostatic ion-acoustic shocks are investigated using the University of California, Los Angeles, double plasma device: (1) laminar shocks; (2) small amplitude turbulent shocks in which the turbulence is confined to be upstream of the shock potential jump; and (3) large amplitude turbulent shocks in which the wave turbulence occurs throughout the shock transition. The wave turbulence is generated by ions which are reflected from the shock potential; linear theory spatial growth increments agree with experimental values. The experimental relationship between the shock Mach number and the shock potential is shown to be inconsistent with theoretical shock models which assume that the electrons are isothermal. Theoretical calculations which assume a trapped electron equation of a state and a turbulently flattened velocity distribution function for the reflected ions yields a Mach number vs potential relationship in agreement with experiment.

Means, R. W.↗

NASA NTRS1976

Analysis of experimental results of the inlet for the NASA hypersonic research engine aerothermodynamic integration model

An aerodynamic engine inlet analysis was performed on the experimental results obtained at nominal Mach numbers of 5, 6, and 7 from the NASA Hypersonic Research Engine (HRE) Aerothermodynamic Integration Model (AIM). Incorporation on the AIM of the mixed-compression inlet design represented the final phase of an inlet development program of the HRE Project. The purpose of this analysis was to compare the AIM inlet experimental results with theoretical results. Experimental performance was based on measured surface pressures used in a one-dimensional force-momentum theorem. Results of the analysis indicate that surface static-pressure measurements agree reasonably well with theoretical predictions except in the regions where the theory predicts large pressure discontinuities. Experimental and theoretical results both based on the one-dimensional force-momentum theorem yielded inlet performance parameters as functions of Mach number that exhibited reasonable agreement. Previous predictions of inlet unstart that resulted from pressure disturbances created by fuel injection and combustion appeared to be pessimistic.

Andrews, E. H., Jr.↗

NASA NTRS1975

A three-parameter analytic phase function for multiple scattering calculations

A very simple procedure has been developed to fit the first three moments of an actual phase function with a three-parameter analytic phase function. The exact Legendre polynomial decomposition of this function is known which makes it quite suitable for multiple scattering calculations. The use of this function can be expected to yield excellent flux values at all depths within a medium. Since it is capable of reproducing the glory, it can be used in synthetic spectra computations from planetary atmospheres. Accurate asymptotic radiance values can also be achieved as long as the single scattering albedo is not less than 0.9.

Kattawar, G. W.↗

NASA NTRS1977

A model for microwave intensity propagation in an inhomogeneous medium

A combined analytic and phenomenological approach, utilizing Maxwell's equations in the Born approximation with radiative transfer theory, is used to describe the propagation of microwave intensity in a scattering medium characterized by three-dimensional random fluctuations in refractive index, as well as nonrandom variations in permittivity, temperature, and loss. This approach yields microwave intensities as a function of polarization, direction, and position. Numerical techniques are presented to solve the transport equations, which include cases of spatially varying coefficients, and highly peaked phase functions. Some computed results illustrating the behavior of microwave intensity in various media are presented. Included are the angular and frequency spectra of thermal emission from semi-infinite media, and the diffuse transmission and reflection response of a scattering layer. The effects of scatterer geometry and scale sizes; correlation function; and gradients in temperature, loss, and scattering parameters are also demonstrated. This model should be particularly useful in interpreting active and passive remote sensing data.

Fisher, A. D.↗

NASA NTRS1980

Relating viscosity to polymer concentration

Equation developed by VanDijk and first applied to viscosity of Newtonian suspension of rigid particles by Eilers is rearranged to yield intrinsic viscosity as explicit function of polymer concentration in polymer solvent system. Experiments have shown relationship valid for polymer solutions having relative viscosities ranging from 1 to 100.

Fedors, R. F.↗

NASA NTRS1979

Effect of variable energy input on nitrogen fixation in instantaneous linear discharges

The reported analysis implies that the number of molecules of NO produced per joule of discharge varies with input energy. The calculations assume a cylindrical symmetry but the results are consistent with equivalent calculations using spherical symmetry. If NO yield does vary with input energy, extrapolation of laboratory experiments using small sparks is not as straightforward as has previously been assumed. Calculated curves for the yield of NO as a function of discharge energy are presented and are compared with experimental values and other theoretical values.

Chameides, W. L.↗

NASA NTRS1978

Thorium concentrations in the lunar surface. II - Deconvolution modeling and its application to the regions of Aristarchus and Mare Smythii

The broad angular response which characterized the Apollo gamma ray spectrometer resulted in a loss of spatial resolution and some of the contrast in determining surface concentrations within lunar regions small compared to the field of view. A deconvolution technique has been developed which removes much of this instrumental effect, thereby improving both spatial resolution and accuracy at the cost of a loss in precision. Geometric models of regional thorium distribution are convoluted through the response function of the instrument to yield a predicted distribution which is compared with the observed data field for quality of fit. Application to areas which include Aristarchus and Mare Smythii confirm some geological relationships and fail to support others.

Haines, E. L.↗

NASA NTRS1981

Fuel spray measurements with an imaging-type spray analyzer

The application of an imaging-type, automated spray analysis system to measurements of fuel sprays requires consideration of a number of significant factors both in its use and in the interpretation of the data. These factors are reviewed and a procedure developed for one such instrument is described. The procedure involves optical scans along the optic axis of the system and an appropriate mathematical inversion scheme for interpretation of the results. The system is nominally capable of yielding the local size distribution function and the total number density at points along the optic axis for droplets from about 10 to 500 microns. No assumptions regarding the form of the size distribution function or the symmetry of the spray are required.

Skifstad, J. G.↗

NASA NTRS1983

Effect of particle presence on the incompressible inviscid flow through a two dimensional compressor cascade

A computational model for calculating the flow field, in the presence of solid particles, through a two dimensional compressor cascade is presented. The method treats the particle phase in the Lagrangian system and the fluid phase in the Eulerian system. The equations of momentum of the fluid phase are modified to account for the momentum exchange between the two phases. The resulting modified momentum and continuity equations are reduced to the conventional stream function-vorticity formulation. The analysis yields the change in the blade surface pressure distribution, the total pressure and velocity in the flow field. Based on this, it is possible to predict the decrease in compressor performance under the presence of particles.

Balan, C.↗

NASA NTRS1983

A note on the oxygen gradient in NGC 628

The Kitt Peak 2.1-m telescope and Intensified Image Dissector Scanner have been used to gather spectrophotometric data in the 3600-5200 A spectral region for five H II regions in the spiral galaxy NGC 628. The Pagel et al (1979) technique was then applied to determine the relative number abundances of O to H in each of the H II regions. An examination of the abundance values obtained as a function of the radial coordinate yields an O gradient of -0.05 + or - 0.03 dex/kpc.

Talent, D. L.↗

NASA NTRS1986

Collision strengths for the intercombination lines of S III

The collision strengths of intercombination lines of S III ions observed in the Io torus are calculated on the basis of data gathered by Voyager instruments, the IUE and the Faint Object Telescope. The doubly ionized ions are excited by electron impacts and move from the 3P2P(3) ground state to excited 3s3P3(1)PO, (1)DO, 3p3d(1)PO, and 3p4s(1)PO states. Excitational cross sections are calculated with a two-state close-coupling approximation for the energy range up to 1,000,000 K, with target states being represented by multiconfiguration interaction wave functions. The close-coupling approximation regarded as an accurate technique because of the dominance of the Coulomb factor in the ionized state. The wave function calculations are estimated to yield values accurate to within 30 percent. Further work is need to quantify the magnitude of error introduced by resonance contributions to the collision strengths.

Ho, Y. K.↗

NASA NTRS1990

A new approach to active vibration isolation for microgravity space experiments

A new method was developed to design an active vibration isolation system for microgravity space experiments. This method yields the required controller transfer functions for a specified transmissibility ratio. Hence, it is a straightforward task to guarantee that the desired vibration isolation performance is achieved at each frequency. The theory for such a controller design was presented by considering a single degree of freedom system. In addition, the magnitude of the input required by the new method has been found to be less than that used by a standard phase lead/lag compensator.

Sinha, Alok↗

NASA NTRS1989

Semidiscrete Galerkin modelling of compressible viscous flow past a circular cone at incidence

A numerical study of the laminar and compressible boundary layer, about a circular cone in a supersonic free stream, is presented. It is thought that if accurate and efficient numerical schemes can be produced to solve the boundary layer equations, they can be joined to numerical codes that solve the inviscid outer flow. The combination of these numerical codes is competitive with the accurate, but computationally expensive, Navier-Stokes schemes. The primary goal is to develop a finite element method for the calculation of 3-D compressible laminar boundary layer about a yawed cone. The proposed method can, in principle, be extended to apply to the 3-D boundary layer of pointed bodies of arbitrary cross section. The 3-D boundary layer equations governing supersonic free stream flow about a cone are examined. The 3-D partial differential equations are reduced to 2-D integral equations by applying the Howarth, Mangler, Crocco transformations, a linear relation between viscosity, and a Blasius-type of similarity variable. This is equivalent to a Dorodnitsyn-type formulation. The reduced equations are independent of density and curvature effects, and resemble the weak form of the 2-D incompressible boundary layer equations in Cartesian coordinates. In addition the coordinate normal to the wall has been stretched, which reduces the gradients across the layer and provides high resolution near the surface. Utilizing the parabolic nature of the boundary layer equations, a finite element method is applied to the Dorodnitsyn formulation. The formulation is presented in a Petrov-Galerkin finite element form and discretized across the layer using linear interpolation functions. The finite element discretization yields a system of ordinary differential equations in the circumferential direction. The circumferential derivatives are solved by an implicit and noniterative finite difference marching scheme. Solutions are presented for a 15 deg half angle cone at angles of attack of 5 and 10 deg. The numerical solutions assume a laminar boundary layer with free stream Mach number of 7. Results include circumferential distribution of skin friction and surface heat transfer, and cross flow velocity distributions across the layer.

Meade, Andrew James, Jr.↗

NASA NTRS1990

A new approach to controller design for microgravity isolation systems

A new method has been developed to design an active vibration isolation system for microgravity space experiments. This method yields the required controller transfer functions for a specified transmissibility. Hence, it is a straightforward task to guarantee that the desired vibration isolation performance is achieved at each frequency. The theory for such a controller design has been presented by considering a single degree of freedom system. The magnitude of the control force required by the new method has been found to be less than that used by a standard phase lead/lag compensator.

Sinha, A.↗

NASA NTRS1991

Plasma convection and ion beam generation in the plasma sheet boundary layer

Because of the dawn-dusk electric field E(dd), plasma in the magnetotail convects from the lobe toward the central plasma sheet (CPS). In the absence of space or velocity diffusion due to plasma turbulence, convection would yield a steady state distribution function f = V exp (-2/3) g(v exp 2 V exp 2/3), where V is the flux tube volume. Starting with such a distribution function and a plasma beta which varies from beta greater than 1 in the CPS to beta much smaller than 1 in the lobe, the evolution of the ion distribution function was studied considering the combined effects of ion diffusion by kinetic Alfven waves (KAW) in the ULF frequency range (1-10 mHz) and convection due to E(dd) x B drift in the plasma sheet boundary layer (PSBL) and outer central plasma sheet (OCPS). The results show that, during the early stages after launching the KAWs, a beamlike ion distribution forms in the PSBL and at the same time the plasma density and temperature decrease in the OCPS. Following this stage, ions in the beams convect toward the CPS resulting in an increase of the plasma temperature in the OCPS.

Moghaddam-Taaheri, E.↗

NASA NTRS1991

A numerical method for unsteady aerodynamics via acoustics

Formal solutions to the wave equation may be conveniently described within the framework of generalized function theory. A generalized function theory is used to yield a formulation and formal solution of a wave equation describing oscillation of a flat plate from which a numerical method may be derived.

Hodge, Steve↗

NASA NTRS1992

Klein-Gordon equation and reflection of Alfven waves in nonuniform media

A new analytical approach is presented for assessing the reflection of linear Alfven waves in smoothly nonuniform media. The general one-dimensional case in Cartesian coordinates is treated. It is shown that the wave equations, upon transformation into the form of the Klein-Gordon equation, display a local critical frequency for reflection. At any location in the medium, reflection becomes strong as the wave frequency descends past this characteristic frequency set by the local nonuniformity of the medium. This critical frequecy is given by the transformation as an explicit function of the Alfven velocity and its first and second derivatives, and hence as an explicit spatial function. The transformation thus directly yields, without solution of the wave equations, the location in the medium at which an Alfven wave of any given frequency becomes strongly reflected and has its propagation practically cut off.

Musielak, Z. E.↗

NASA NTRS1992

Comparison of measured and modeled solar EUV flux and its effect on the E-F1 region ionosphere

Two different photochemical schemes are used to investigate the response of the E-F1 region ionosphere to different solar EUV flux models, and the results are compared with incoherent scatter radar electron density measurements taken at Millstone Hill. The latest EUV flux model (Tobiska, 1991), which incorporates more recent measurements, has generally more flux at short wavelengths compared to the Hinteregger et al. (1981) flux model based on AE-E satellite data. This results in better agreement with the measurements in the E-F1 region and above. The Tobiska flux model gives a smaller E region peak density, due to the influence of low Ly-beta flux in the November 10, 1988 rocket measurements of Woods and Rottman (1990). The photoionization and photoabsorption cross sections of Conway (1988) give results in somewhat better agreement with observations than the cross sections of Torr et al. (1979). For the zenith angles considered (daytime conditions), the Chapman function method for calculating photoabsorption yields results in satisfactory agreement with a more rigorous calculation method using a formula from Rees (1989).

Buonsanto, M. J.↗