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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 613 records · Page 34

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NASA NTRS1979

Correlation of data related to shock-induced trailing-edge separation and extrapolation to flight Reynolds number

Pressure data from a number of previous wind tunnel and flight investigations of high speed transport type wings were analyzed with the intent of developing a procedure for extrapolating low Reynolds number data to flight conditions. These analyses produced a correlation of the development of trailing-edge separation resulting from increases in Mach number and/or angle of attack and show that scale effects on this correlated separation development and the resulting shock location changes fall into a regular and apparently universal pattern. Further studies appear warranted to refine the correlation through a detailed consideration of boundary layer characteristics, and to evaluate scale effects on supercritical wings.

Cahill, J. F.↗

NASA NTRS1978

A design point correlation for losses due to part-span dampers on transonic rotors

The design-point losses caused by part-span dampers were correlated for 21 transonic axial-flow fan rotors that had tip speeds varying from 350 to 488 meters per second and design pressure ratios of 1.5 to 2.0. The additional loss attributable to the damper and the total region along the blade height influenced were correlated with selected aerodynamic and geometric parameters. The maximum damper loss correlated well with the mean inlet Mach number at the damper location, the geometric parameters of leading- and trailing-edge damper radius normalized by mean passage height and damper aerodynamic chord, respectively, and the aerodynamic loading parameter of the blade camber divided by the solidity at the damper location. The region of damper influence extended over a mean passage height of the order of 10 to 15 times the maximum damper thickness.

Roberts, W. B.↗

NASA NTRS1978

Correlation studies of four submicron OH airglow bands during Spacelab simulation

The (7-2), (8-3), (5-1) and (6-2) bands of OH were observed from NASA's CV-990 aircraft during the Spacelab Simulation Mission. Both the average intensity and the fluctuations in intensity of each band were found to be strongly correlated to those of all other bands observed, suggesting that the excitation mechanisms for these bands are not independent processes. No significant correlation was observed between airglow intensity and latitude, azimuth, or local time for the ranges accessible during these flights. An additional ground-based experiment revealed a comparable correlation between the (6-0) and (8-3) bands.

Kieffaber, L. M.↗

NASA NTRS1979

Optical correlation of surface displacement

A coherent optical correlation technique is used to measure surface displacements. In the event that the surface roughness of the test object is invariant during the object's translation, the correlation intensity peak remains constant. A simple relationship between the displacement of the surface and the displacement of the peak correlation signal is found and experimentally verified.

Owen, R. B.↗

NASA NTRS1978

A new color correlation method applied to XRF Al/Si ratios and other lunar remote sensing data

Orbital X-ray fluorescence Al/Si intensity ratios, corrected for variations in solar activity, are correlated with normal albedo, elevation measurements from laser altimetry data, and gamma ray data in the 2.75-8.60 MeV range. Each of these data sets is placed into a digital array consisting of 1/4 deg latitude by 1/4 deg longitude pixels. Information relative to the correlation of Al/Si ratios with each of the other data sets is presented in the following forms: (1) histograms are given for each data set to show the frequency distribution within the areas of common coverage; (2) density plots are produced from the plot of a two-dimensional array consisting of the Al/Si ratio vs the other parameter value for each pixel; and (3) color correlation maps are produced by placing the two-dimensional array into a 3 x 3 matrix consisting of nine equal subarrays containing an equal number of data points.

Clark, P. E.↗

NASA NTRS1980

Off-design correlation for losses due to part-span dampers on transonic rotors

Experimental data from 10 transonic fan rotors were used to correlate losses created by part-span dampers located near the midchord position on the rotor blades. The design tip speed of these rotors varied from 419 to 425 m/sec, and the design pressure ratio varied from 1.6 to 2.0. Additional loss caused by the dampers for operating conditions between 50 and 100 percent of design speed were correlated with relevant aerodynamic and geometric parameters. The resulting correlation predicts the variation of total-pressure-loss coefficient in the damper region to a good approximation.

Roberts, W. B.↗

NASA NTRS1979

A new approach to the correlation of boundary layer mass transfer rates with thermal diffusion and/or variable properties

A rational approach to the correlation of boundary layer mass transport rates, applicable to many commonly encountered laminar flow conditions with thermal diffusion and/or variable properties, is outlined. The correlation scheme builds upon already available constant property blowing/suction solutions by introducing appropriate correction factors to account for the additional ('pseudo' blowing and source) effects identified with variable properties and thermal diffusion. Applications of the scheme to the particular laminar boundary layer mass transfer problems considered herein (alkali and transition metal compound vapor transport) indicates satisfactory accuracy up to effective blowing factors equivalent to about one third of the 'blow off' value. As a useful by-product of the variable property correlation, we extend the heat-mass transfer analogy, for a wide range of Lewis numbers, to include variable property effects.

Srivastava, R.↗

NASA NTRS1979

Classification results using spacially correlated Landsat data

Tubbs and Coberly (1978) demonstrated that Landsat multispectral scanner data are not independent random observations, but, are in fact highly correlated. They also demonstrated that the correlation structure for the data is similar to that of a stationary autoregressive process of order one. This paper investigates the effect that serially correlated training data have upon both the estimation of parameters and the classification problem. Results are included for both the Bayesian and maximum likelihood classification procedures.

Tubbs, J. D.↗

NASA NTRS1980

Structural mapping from MSS-LANDSAT imagery: A proposed methodology for international geological correlation studies

A methodology is proposed for international geological correlation studies based on LANDSAT-MSS imagery, Bullard's model of continental fit and compatible structural trends between Northeast Brazil and the West African counterpart. Six extensive lineaments in the Brazilian study area are mapped and discussed according to their regional behavior and in relation to the adjacent continental margin. Among the first conclusions, correlations were found between the Sobral Pedro II Lineament and the megafaults that surround the West African craton; and the Pernambuco Lineament with the Ngaurandere Linemanet in Cameroon. Ongoing research to complete the methodological stages includes the mapping of the West African structural framework, reconstruction of the pre-drift puzzle, and an analysis of the counterpart correlations.

Dejesusparada, N.↗

NASA NTRS1980

The structure of correlation tensors in homogeneous anisotropic turbulence

The study of turbulence with spatially homogeneous but anisotropic statistical properties has applications in space physics and laboratory plasma physics. The first step in the systematic study of such fluctuations is the elucidation of the kinematic properties of the relevant statistical objects, which are the correlation tensors. The theory of isotropic tensors, developed by Robertson, Chandrasekhar and others, is reviewed and extended to cover the general case of turbulence with a pseudo-vector preferred direction, without assuming mirror reflection invariance. Attention is focused on two point correlation functions and it is shown that the form of the decomposition into proper and pseudo-tensor contributions is restricted by the homogeneity requirement. It is also shown that the vector and pseudo-vector preferred direction cases yield different results. An explicit form of the two point correlation tensor is presented which is appropriate for analyzing interplanetary magnetic fluctuations. A procedure for determining the magnetic helicity from experimental data is presented.

Matthaeus, W. H.↗

NASA NTRS1978

A correlation method to predict the surface pressure distribution on an infinite plate from which a jet is issuing

A correlation method to predict pressures induced on an infinite plate by a jet issuing from the plate into a subsonic free stream was developed. The complete method consists of an analytical method which models the blockage and entrainment properties of the jet and a correlation which accounts for the effects of separation. The method was developed for jet velocity ratios up to ten and for radial distances up to five diameters from the jet. Correlation curves and data comparisons are presented for jets issuing normally from a flat plate with velocity ratios one to twelve. Also, a list of references which deal with jets in a crossflow is presented.

Perkins, S. C., Jr.↗

NASA NTRS1981

Developing new architectures for the Block 2 VLBI correlator system

The overall LSI (large-scale integrated circuits) architecture design and current status of the VBLI (very long baseline interferometry) block 2 correlator is addressed. The VBLI correlator algorithms demand a computing system that provides a throughput of hundreds of millions of instructions per second to perform cross-correlation detection for six baselines. The LSI technology lights the way for the computation of complex parallel process and is raising the upper bound of computerization.

Peterson, J. C.↗

NASA NTRS1980

HOE/lensless matched spatial filter wavelength-scaling correlator

A scaling correlator optical pattern recognition system is described in which a lensless matched spatial filter (with the second Fourier transform lens and the matched spatial filter recorded on the same plate) is used with a first Fourier transform lens that is also an holographic optical element. The matched spatial filter is recorded at one wavelength and correlation is obtained at a second wavelength. Experimental demonstration and output correlation SNR data are reported, together with a comparison of the system's noise level using conventional optics and holographic elements.

Shen, M.↗

NASA NTRS1981

Asymptotic form of the longitudinal correlation function for isotropic homogeneous turbulence

An asymptotic form is derived for the longitudinal correlation function for isotropic homogeneous turbulence in an incompressible fluid governed by the Navier-Stokes equation. The result is obtained from an analysis of the algebraic-differential structure of the two-point correlation tensor contained in the complex-valued Fourier transform of the probability measure over the turbulence ensemble, which reveals that the Hopf characteristic functional (the complex-valued Fourier transform of the probability measure) satisfies the Fourier interference inequality. Consequences of the expression obtained, in which the correlation function is a positive definite function of the inverse cube of the spatial coordinate as it approaches infinity, are shown to include the nonexistence of the Loitsianskii invariant, and the solution is shown to be consistent with empirical formulas.

Rosen, G.↗

NASA NTRS1981

Buckling of composite cylinders under combined compression and torsion Theoretical/experimental correlation

Elastic buckling loads for laminated composite circular cylindrical shells under combined axial compression and torsion are plotted on a dimensionless load plane and determined experimentally from boron/epoxy and graphite/epoxy specimens with symmetric and asymmetric layups. Good correlation is achieved between the theoretical and experimental interaction curves. The theoretical buckling loads are obtained from Fluegge's cylindrical shell equations and for pure torsion there is good correlation, but for the pure axial compression the correlation is rather poor.

Herakovich, C. T.↗

NASA NTRS1981

Structure of correlation tensors in homogeneous anisotropic turbulence

The theory of isotropic tensors, developed by Robertson (1940), Batchelor (1946), and Chandrasekhar (1951), is extended to cover the general case of turbulence with a pseudo-vector-preferred direction, without assuming mirror-reflection invariance. Attention is focused on two-point-correlation functions, and it is shown that the form of the decomposition into proper and pseudo-tensor contributions is restricted by the homogeneity requirement. The somewhat unexpected result that the vector- and pseudo-vector-preferred-direction cases yield different results is presented: A pseudo-vector-preferred direction allows the correlation matrix one more functional degree of freedom than does the proper vector case. An explicit form of the two-point-correlation tensor in the presence of a uniform mean magnetic field is presented which may be appropriate for use in analysis of magnetic fluctuations in plasma containment devices or the interplanetary medium. A procedure for determining the magnetic helicity from experimental data is presented.

Matthaeus, W. H.↗

NASA NTRS1981

Interferometric surface-wave acousto-optic time-integrating correlators

A structure for a coherent-interferometric acousto-optic (AO) time-integrating correlator was implemented by using a single surface acoustic wave (SAW) device with tilted transducers to reduce intermodulation terms. The SAW device was fabricated on Y-Z LiNbO3 with a center frequency of 175 MHz, a bandwidth of 60 MHz, and a time aperture of about 10 micros. The density of the photodetector array, with a potential of 120 MHz. Typical integration times are 30 to 40 ms, providing processing gains in excess of 10 to the 6th power. Such a device is useful in providing fast synchronization of communication links and in demodulating to base band and simultaneously acting as a synchronization lock monitor for moderate data rates. Where processing may be limited by Doppler shifts, a two dimensional architecture was implemented to allow full processing gain. Two one-dimensional, SAW AO time-integrating correlators and a two dimensional correlator are evaluated.

Berg, N. J.↗

NASA NTRS1982

LIMS Instrument Package (LIP) balloon experiment: Nimbus 7 satellite correlative temperature, ozone, water vapor, and nitric acid measurements

The Limb Infrared Monitor of the Stratosphere (LIMS) LIP balloon experiment was used to obtain correlative temperature, ozone, water vapor, and nitric acid data at altitudes between 10 and 36 kilometers. The performance of the LIMS sensor flown on the Nimbus 7 Satellite was assessed. The LIP consists of the modified electrochemical concentration cell ozonesonde, the ultraviolet absorption photometric of ozone, the water vapor infrared radiometer sonde, the chemical absorption filter instrument for nitric acid vapor, and the infrared radiometer for nitric acid vapor. The limb instrument package (LIP), its correlative sensors, and the resulting data obtained from an engineering and four correlative flights are described.

Lee, R. B., III↗