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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

A study of viscous flow in stator and rotor passages

A numerical technique to predict the viscous behavior in the three-dimensional domain of rotating and stationary blade passages is presented. The analysis is based upon the numerical integration of the incompressible Navier-Stokes equations. An approach is taken to combine the three momentum equations and the continuity equation into two sets of vorticity transport-stream function equations. These equations are expressed along families of arbitrarily defined orthogonally intersecting surfaces placed within the blade passage. Unlike the stream surfaces, the arbitrary surfaces allow fluid to flow across. The numerical code employs a nonorthogonal body fitted coordinate system on each of the intersecting surfaces. The solution process involves the iterative combination of the solutions on the two families of intersecting surfaces for a complete solution. The results of flow in thin blade stationary and rotating polar ducts is presented.

Sheoran, Y.↗
NASA NTRS1991

Algebraic grid generation for complex geometries

An efficient computer program called GRID2D/3D has been developed to generate single and composite grid systems within geometrically complex two- and three-dimensional (2D and 3D) spatial domains that can deform with time. GRID2D/3D generates single grid systems by using algebraic grid generation methods based on transfinite interpolation. The distribution of grid points within the spatial domain is controlled by stretching functions and grid lines can intersect boundaries of the spatial domain orthogonally. GRID2D/3D generates composite grid systems by patching together two or more single grid systems. The patching can be discontinuous or continuous. For 2D spatial domains the boundary curves are constructed by using either cubic or tension spline interpolation. For 3D spatial domains the boundary surfaces are constructed by using a new technique, developed in this study, referred to as 3D bidirectional Hermite interpolation.

Shih, T. I.-P.↗
NASA NTRS1994

On determining the spectrum of primordial inhomogeneity from the COBE DMR sky maps: Method

The natural approach to a spectral analysis of data distributed on the sky employs spherical harmonic decomposition. A common problem encountered in practical astronomy is the lack of full sky coverage in the available data. For example, the removal of the Galactic plane data from the Cosmic Background Explorer (COBE) Differential Microwave Radiometer (DMR) sky maps compromises Fourier analysis of the cosmic microwave background (CMB) temperature distribution due to the loss of orthogonality of the spherical harmonics. An explicit method for constructing orthonormal functions on an incomplete (e.g., Galaxy-cut) sphere is presented. These functions should be used in the proper Fourier analysis of the COBE DMR sky maps to provide the correct input for the determination of the spectrum of primordial inhomogeneity. The results of such an analysis are presented in an accompanying Letter. A similar algebraic construction of appropriate functions can be devised for other astronomical applications.

Gorski, Krzysztof M.↗
NASA NTRS2022

Characterization of Rochon Prisms for Bi-Directional Imaging Applications

Polarizing prisms are often used in applications where light is split into two separate beams of orthogonal polarization, or to isolate a beam with a preferred polarization state. These prisms are typically used with lasers, but there are applications of their use with imaging systems. One such example is that of a recently developed focusing schlieren system, where light must be transmitted through a Rochon prism in both the forward and backward directions. Three Rochon prisms were characterized in this study in terms of their transmitted intensity and polarization state: a quartz/quartz prism, a glass/quartz prism, and a MgF2/MgF2 prism. Laser testing at four wavelengths was performed, along with full clear aperture collimated LED light testing at a single wavelength. The glass/quartz and MgF2/MgF2 prisms operated in the same manner when light was transmitted in either the forward or backward direction. The quartz/quartz prism, however, exhibited differences between operation in the forward and backward direction. In the forward orientation for input plane polarized light, the transmitted intensity varied sinusoidally as a function of height of incidence through the prism, while the polarization of the unrefracted and refracted beams were uniform and orthogonally polarized. In the backward orientation, the intensity for both unrefracted and refracted beams was uniform, but the azimuthal orientation of the output plane polarized light varied sinusoidally as a function of height of incidence through the prism, while remaining orthogonally polarized between the two beams at each position.

Joshua M Weisberger↗
NASA NTRS1978

Modal content of noise generated by a coaxial jet in a pipe

Noise generated by air flow through a coaxial obstruction in a long, straight pipe was investigated with concentration on the modal characteristics of the noise field inside the pipe and downstream of the restriction. Two measurement techniques were developed for separation of the noise into the acoustic duct modes. The instantaneous mode separation technique uses four microphones, equally spaced in the circumferential direction, at the same axial location. The time-averaged mode separation technique uses three microphones mounted at the same axial location. A matrix operation on time-averaged data produces the modal pressure levels. This technique requires the restrictive assumption that the acoustic modes are uncorrelated with each other. The measured modal pressure spectra were converted to modal power spectra and integrated over the frequency range 200-6000 Hz. The acoustic efficiency levels (acoustic power normalized by jet kinetic energy flow), when plotted vs. jet Mach number, showed a strong dependence on the ratio of restriction diameter to pipe diameter. The acoustic energy flow analyses based on the thermodynamic energy equation and on the results of Mohring both resulted in orthogonality properties for the eigenfunctions of the radial mode shape equation. These orthogonality relationships involve the eigenvalues and derivatives of the radial mode shape functions.

Kerschen, E. J.↗
NASA NTRS1985

Objectives and design of the Echo 6 electron beam experiment - Large ionospheric perturbations and energetic particle patterns

The data from the March 30, 1983 launching of Echo 6 are presented. Echo 6 contained duplex accelerators and a system of four throw away detectors to detect and analyze conjugate electron echoes. The model used to calculate the proper trajectory of the rocket and the reason for not detecting echoes are discussed. The components of the plasma diagnostic package which was used to study the electron beam interactions with the ionospheric plasma, and the functions of the two controllable electron guns and the two sets of orthogonal electric probes are described. The signal-mode potentials between each probe and the plasma diagnostic payload are investigated. The signals produced by the gun pulses are analyzed and the interpretation of the electric field probe response is examined.

Winckler, J. R.↗
NASA NTRS1992

Characteristics of obliquely propagating, nonlinear Alfven waves

Consideration is given to properties of obliquely propagating (with respect to the large-scale magnetic field) nonlinear Alfven and fast magnetosonic waves as described by the derivative nonlinear Schroedinger equation. The focus is on those waves which in the parallel-propagating limit are circularly polarized, exact solutions to the MHD equations. Results are presented of a study of the changes in the structure of these waves as the propagation angle is increased. Attention is also given to the evolution of initial conditions which do not correspond to stationary wave propagations. It is found that, as the propagation angle with respect to the mean field increases, the functional forms of the wave magnetic field components in the two directions orthogonal to the propagation direction become increasingly dissimilar. The angle about the mean field within which stationary waves resemble parallel-propagating, circularly polarized waves becomes smaller as the wavelength increases. If the 'initial condition' wave train is close to parallel-propagating, then there is little subsequent evolution in its form.

Spangler, Steven R.↗
NASA NTRS2005

Identification of Cyclically Symmetric Resonance in Experimental Data for Engine Failure Analysis

Many structural components are rotationally symmetric. For a perfectly manufactured structure, the modal wave shapes are exactly sinusoidal. These structures can be excited by similarly-shaped forcing functions such as those found frequently in or near turbomachinery. Due to orthogonality, resonance occurs only when the integer wave number of the structure equals the integer wave number of the excitation as well as when the excitation frequency is close to the natural frequency of the mode. This resonance can lead to high-cycle fatigue (HCF) cracking of the structure. To help understand this phenomenon, it is desirable to determine the modal composition of the response and excitation. Once the modal composition is known, either the excitation or the structure can be modified to reduce the response and therefore prevent HCF cracking.

Medley, Steve↗
NASA NTRS1993

Hierarchical structure analysis of interstellar clouds using nonorthogonal wavelets

We introduce the use of Laplacian pyramid transforms, a form of nonorthogonal wavelets, to analyze the structure of interstellar clouds. These transforms are generally better suited for analyzing structure than orthogonal wavelets because they provide more flexibility in the structure of the encoding functions - here circularly symmetric bandpass filters. This technique is applied to CO maps of Barnard 5. In the (C-13)O maps, for example, we identify 60 different fragments and clumps, as well as several cavities, or bubbles. Many features show evidence of hierarchical structure, with most of the power in the largest wavelengths. The clumps have a more chaotic structure at small wavelengths than expected for Kolmogorov turbulence, and a mass distribution proportional to M exp -5/3. The structure analysis is consistent with a picture where gravity, energy injection, compressible turbulence, and coalescence play an important role in the dynamics of B5.

Langer, William D.↗
NASA NTRS1975

Spatially multiplexed infrared camera

A spatially multiplexed infrared camera is described. The camera records an image by measuring the coefficients of an orthogonal series expansion of the two-dimensional radiance distribution. By choice of appropriate functions, significant gains in the picture signal-to-noise ratio can be realized. We have constructed a camera utilizing this multiplexing principle to record images of astronomical objects at infrared wavelengths, where conventional scanning systems perform badly because of low signal levels. Test results verify that the camera exhibits the increase of efficiency expected of a multiplexing system, allowing exposure times two orders of magnitude shorter than necessary for comparable scanning systems.

Davies, D. W.↗
NASA NTRS1987

Statistics of Sxy estimates

The statistics of Sxy estimates derived from orthogonal-component measurements are examined. Based on results of Goodman (1957), the probability density function (pdf) for Sxy(f) estimates is derived, and a closed-form solution for arbitrary moments of the distribution is obtained. Characteristic functions are used to derive the exact pdf of Sxy(tot). In practice, a simple Gaussian approximation is found to be highly accurate even for relatively few degrees of freedom. Implications for experiment design are discussed, and a maximum-likelihood estimator for a posterior estimation is outlined.

Freilich, M. H.↗
NASA NTRS2019

Meshless Local Petrov-Galerkin (MLPG) Method with Orthogonal Polynomials for Euler-Bernoulli Beam Problems

In this paper, the feasibility of orthogonal polynomials in the meshless local Petrov Galerkin method (MLPG) method is studied. The orthogonal polynomials, Chebyshev and Legendre polynomials, are used in this MLPG method as trial functions. The test functions used were power functions with smooth derivatives at their ends. The performance of these methods is studied by applying these methods to Euler-Bernoulli beam problems. The MLPG-Galerkin and Legendre methods passed all the patch tests for simple beam problems. Next the formulations are tested on complex beam problems such as beams with partial loadings and continuous beam problems. Problems with load discontinuities and additional supports require special attention. Near discontinuities, judicious choice of number of nodes and nodal placements are needed to obtain accurate deflections, slopes, moments and shear forces. As polynomial functions are used, the large number of nodes can create a transformation matrix that is ill-conditioned, resulting in problems with the inversion of the matrix. The conditioning worsens as the number of nodes are increased beyond 20. Quadruple precision was needed for models to obtain accurate solutions. Even with quadruple precision the accuracy of the method suffers as the number of nodes is increased beyond 20. This appears to be a drawback of the MLPG-Chebyshev and MLPG-Legendre methods.

Raju, Ivatury S.↗
NASA NTRS1983

Natural instability of free shear layers

Under controlled small-amplitude excitation, an initially laminar free shear layer experiences maximum growth rate at a Strouhal number St(theta) of 0.017 (consistent with theory) and maximum growth at St(theta) = 0.011, while the natural instability frequency St(theta-n) (of an unexcited shear layer) is found to have an intermediate value. Investigations in both axisymmetric and plane shear layers in a number of independent facilities reveal that the St(theta-n) value falls in the range 0.0125-0.0155, depending on the exit boundary-layer fluctuation level and the spanwise radius of curvature. The St(theta-n) value decreases with increasing jet diameter or exit boundary-layer fluctuation level, but is not a direct function of the exit momentum thickness Reynolds number. For a given facility, the instability details are found to be independent of whether the entrainment at the lip is parallel to the stream or orthogonal (due to the addition of an end plate). The steamwise evolutions of the amplitudes at the fundamental frequency and its harmonics and subharmonics are unique functions of the downstream distance nondimensionalized by the exit momentum thickness, but their details remain functions of the flow geometry (i.e., axisymmetric or plane).

Husain, Z. D.↗
NASA NTRS1970

Design problems of small turbomachinery

Advanced design and testing techniques developed at NASA Lewis to achieve high efficiency in small turbomachines are described. Small radial and axial turbines and compressors were built for space power systems and associated studies at the Lewis Research Center. A six stage axial compressor of 3.5 inches diameter and axial turbines of 5 and 8.5 inches diameter were included. Radial turbines and compressors ranged from 3.5 to 6 inches. Topics discussed include maximum efficiency as a function of speed, the effect of compressibility on passage size, the use of quasi-orthogonals to calculate cross-channel velocity gradients, a design point velocity diagram study for axial turbines, and estimating off-design performance. Special turbine instruments and calibration procedures were developed to test compressors and turbines, to determine Reynolds and size number effects clearance, specific speed effects, and compressor performance. Laboratory tests conducted to study system operation and shaft and bearing motions are also reviewed.

Rohlik, H. E.↗
NASA NTRS1994

Propagation velocities of laser-produced plasmas from copper wire targets and water droplets

Experiments were performed to determine the plasma propagation velocities resulting from KrF laser irradiation of copper wire target (75 microns diameter) and water droplets (75 microns diameter) at irradiance levels ranging from 25 to 150 GW/sq cm. Plasma propagation velocities were measured using a streak camera system oriented orthogonally to the high-energy laser propagation axis. Plasma velocities were studied as a function of position in the focused beam. Results show that both the shape of the plasma formation and material removal from the copper wire are different and depend on whether the targets are focused or slightly defocused (approximately = 0.5 mm movement in the beam axis). Plasma formation and its position relative to the target is an important factor in determining the practical focal point during high-energy laser interaction with materials. At irradiance of 100 GW/sq cm, the air plasma has two weak-velocity components which propagate toward and away from the incident laser while a strong-velocity component propagates away from the laser beam as a detonation wave. Comparison of the measured breakdown velocities (in the range of 2.22-2.27 x 10(exp 5) m/s) for air and the value calculated by the nonlinear breakdown wave theory at irradiance of 100 GW/sq cm showed a quantitative agreement within approximately 50% while the linear theory and Gaussian pulse theory failed. The detonation wave velocities of plasma generated from water droplets and copper wire targets for different focused cases were measured and analyzed theoretically. The propagation velocities of laser-induced plasma liquid droplets obtained by previous research are compared with current work.

Song, Kyo-Dong↗
NASA NTRS1998

Potential and Limitations of the Modal Characterization of a Spacecraft Bus Structure by Means of Active Structure Elements

Theoretical and experimental studies have been performed to investigate the potential and limitations of the modal characterization of a typical spacecraft bus structure by means of active structure elements. The aim of these studies has been test and advance tools for performing an accurate on-orbit modal identification which may be characterized by the availability of a generally very limited test instrumentation, autonomous excitation capabilities by active structure elements and a zero-g environment. The NASA LARC CSI Evolutionary Testbed provided an excellent object for the experimental part of this study program. The main subjects of investigation were: (1) the selection of optimum excitation and measurement to unambiguously identify modes of interest; (2) the applicability of different types of excitation means with focus on active structure elements; and (3) the assessment of the modal identification potential of different types of excitation functions and modal analysis tools. Conventional as well as dedicated modal analysis tools were applied to determine modal parameters and mode shapes. The results will be presented and discussed based on orthogonality checks as well as on suitable indicators for the quality of the acquired modes with respect to modal purity. In particular, the suitability for modal analysis of the acquired frequency response functions as obtained by excitation with active structure elements will be demonstrated with the help of reciprocity checks. Finally, the results will be summarized in a procedure to perform an on-orbit modal identification, including an indication of limitation to be observed.

Grillenbeck, Anton M.↗