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NASA NTRS1993

Photometry and spectroscopy in the open cluster Alpha Persei, 2

Results from a combination of new spectroscopic and photometric observations in the lower main-sequence and pre-main sequence of the open cluster alpha Persei are presented. New echelle spectroscopy has provided radial and rotational velocity information for thirteen candidate members, three of which are nonmembers based on radial velocity, absence of a Li 6707A feature, and absence of H-alpha emission. A set of revised rotational velocity estimates for several slowly rotating candidates identified earlier is given, yielding rotational velocities as low as 7 km/s for two apparent cluster members. VRI photometry for several pre-main sequence members is given; the new (V,V-I(sub K)) photometry yields a more clearly defined pre-main sequence. A list of approximately 43 new faint candidate members based on the (V,V-I(sub K)) CCD photometry is presented in an effort to identify additional cluster members at very low masses. Low-dispersion spectra obtained for several of these candidates provide in some cases supporting evidence for cluster membership. The single brown dwarf candidate in this cluster is for the first time placed in a color-magnitude diagram with other cluster members, providing a better means for establishing its true status. Stars from among the list of new photometric candidates may provide the means for establishing a sequence of cluster members down to very faint magnitudes (V approximately 21) and consequently very low masses. New coordinate determinations for previous candidate members and finding charts for the new photometric candidates are provided in appendices.

Prosser, Charles F.↗

NASA NTRS1994

Photometry and spectroscopy in the open cluster alpha Persei, 2.

Results from a combination of new spectroscopic and photometric observations in the lower main sequence and pre-main sequence of the open cluster alpha Persei are presented. New echelle spectroscopy has provided radial and rotational velocity information for thirteen candidate members, three of which are nonmembers based on radial velocity, absence of a Li 6707 A feature, and absence of H alpha emission. A set of revised rotational velocity estimates for several slowly rotating candidates identified earlier is given, yielding rotational velocities as low as 7 km/s for two apparent cluster members. VI photometry for several pre-main-sequence members is given; the new (V, V-I(sub K) photometry yields a more clearly defined pre-main sequence. A list of approximately 30 new faint candidate members based on the (V, V-I(sub K)), charge coupled device (CCD) photometry is presented in an effort to identify additional cluster members at very low masses. Low-dispersion spectra obtained for several of these candidates provide in some cases supporting evidence for cluster membership. The single brown dwarf candidate in this cluster is for the first time placed in a color-magnitude diagram with other cluster members, providing a better means for establishing its true status. Stars from among the list of new photometric candidates may provide the means for establishing a sequence of cluster members down to very faint magnitudes (V approximately 21) and consequently very low masses. New coordinate determinations for previous candidate members and finding charts for the new photometric candidates are provided in Appendices.

Prosser, Charles F.↗

NASA NTRS1974

Radial gradient of solar wind velocity from 1 to 5 AU

Solar wind velocities have been measured on a daily basis from data obtained by the Ames Research Center plasma analyzers on both Pioneer 10 and Pioneer 11. A comparison between the time profiles of the solar wind velocities observed at the two spacecraft shows that the solar wind has the same major features, such as high velocity streams, out to at least 5 astronomical units (AU) from the sun. Major features in the velocity time profile observed first at Pioneer 11 are seen later at Pioneer 10 with a delay consistent with the respective heliocentric longitudes of the two spacecraft, their radial distances from the sun, and the solar wind velocity. A more detailed comparison between the velocity measurements made at Pioneer 10 and Pioneer 11 shows that the range of solar wind velocities decreases with increasing radial distance from the sun. Although the average value of the solar wind velocity as measured over a sufficiently long period is approximately the same at both spacecraft, the deviations to higher and lower velocities are less at a greater radial distance from the sun.

Collard, H. R.↗

NASA NTRS1988

Laser Anemometer For Turbine Research

Three velocity components measured through one port. Laser anemometer combines conventional interference-fringe anemometer configuration with Fabry-Perot interferometer to enable simultaneous measurement of radial and transverse velocities. Transverse-velocity axis rotated, enabling measurement of both transverse-velocity components. Does not require large optical-access port for measurement of radial velocity.

Seasholtz, Richard G.↗

NASA NTRS1997

Direct Numerical Simulation of Incompressible Pipe Flow Using a B-Spline Spectral Method

A numerical method based on b-spline polynomials was developed to study incompressible flows in cylindrical geometries. A b-spline method has the advantages of possessing spectral accuracy and the flexibility of standard finite element methods. Using this method it was possible to ensure regularity of the solution near the origin, i.e. smoothness and boundedness. Because b-splines have compact support, it is also possible to remove b-splines near the center to alleviate the constraint placed on the time step by an overly fine grid. Using the natural periodicity in the azimuthal direction and approximating the streamwise direction as periodic, so-called time evolving flow, greatly reduced the cost and complexity of the computations. A direct numerical simulation of pipe flow was carried out using the method described above at a Reynolds number of 5600 based on diameter and bulk velocity. General knowledge of pipe flow and the availability of experimental measurements make pipe flow the ideal test case with which to validate the numerical method. Results indicated that high flatness levels of the radial component of velocity in the near wall region are physical; regions of high radial velocity were detected and appear to be related to high speed streaks in the boundary layer. Budgets of Reynolds stress transport equations showed close similarity with those of channel flow. However contrary to channel flow, the log layer of pipe flow is not homogeneous for the present Reynolds number. A topological method based on a classification of the invariants of the velocity gradient tensor was used. Plotting iso-surfaces of the discriminant of the invariants proved to be a good method for identifying vortical eddies in the flow field.

Loulou, Patrick↗

NASA NTRS1977

An empirical model for the solar wind velocity

An analytic expression for the average radial component of the Solar Wind velocity between 1 solar radius and 1 AU is developed. The model is constructed by assuming the conservation of particle flow in the Solar Wind and application of a twelve-year average measured value of the Solar Wind radial velocity at 1 AU.

Berman, A. L.↗

NASA NTRS1972

Turbulent boundary layer on a rotating helical blade.

Investigation of the boundary-layer characteristics on a helical blade of large chord length, enclosed in an annulus and rotating in a fluid otherwise at rest. The three-dimensional form of momentum integral equations is derived, and is used to predict the boundary-layer growth and limiting streamline angles on the blade surface. The measurements are in general agreement with the predictions. The wall shear stress correlation, which includes both Reynolds number and rotation parameters, valid for a rotating blade operating at zero pressure gradient, is derived. Radial and tangential velocity profiles, the tangential component of turbulence intensity, and blade static pressures are measured at several locations on the blade surface. The nature of flow near the blade tip is discussed. An expression for the radial velocity profile, valid in the outer region of the boundary layer, is derived theoretically.

Lakshminarayana, B.↗

NASA NTRS1989

Numerical studies of the effects of jet-induced mixing on liquid-vapor interface condensation

Numerical solutions of jet-induced mixing in a partially full cryogenic tank are presented. An axisymmetric laminar jet is discharged from the central part of the tank bottom toward the liquid-vapor interface. Liquid is withdrawn at the same volume flow rate from the outer part of the tank. The jet is at a temperature lower than the interface, which is maintained at a certain saturation temperature. The interface is assumed to be flat and shear-free and the condensation-induced velocity is assumed to be negligibly small compared with radial interface velocity. Finite-difference method is used to solve the nondimensional form of steady state continuity, momentum, and energy equations. Calculations are conducted for jet Reynolds numbers ranging from 150 to 600 and Prandtl numbers ranging from 0.85 to 2.65. The effects of above stated parameters on the condensation Nusselt and Stanton numbers which characterize the steady-state interface condensation process are investigated. Detailed analysis to gain a better understanding of the fundamentals of fluid mixing and interface condensation is performed.

Lin, Chin-Shun↗

NASA NTRS1989

Recovering the full velocity and density fields from large-scale redshift-distance samples

A new method for extracting the large-scale three-dimensional velocity and mass density fields from measurements of the radial peculiar velocities is presented. Galaxies are assumed to trace the velocity field rather than the mass. The key assumption made is that the Lagrangian velocity field has negligible vorticity, as might be expected from perturbations that grew by gravitational instability. By applying the method to cosmological N-body simulations, it is demonstrated that it accurately reconstructs the velocity field. This technique promises a direct determination of the mass density field and the initial conditions for the formation of large-scale structure from galaxy peculiar velocity surveys.

Bertschinger, Edmund↗

NASA NTRS1989

Numerical studies of the effects of jet-induced mixing on liquid-vapor interface condensation

Lin, Chin-Shun↗

NASA NTRS1991

Vapor condensation at the free surface of an axisymmetric liquid mixed by a laminar jet

This paper presents numerical solutions of jet-induced mixing in a partially full cryogenic tank. An axisymmetric laminar jet is discharged from the central part of the tank bottom toward the liquid-vapor interface. Liquid is withdrawn at the same volume flow rate from the outer part of the tank. The jet is at a temperature lower than the interface, which is maintained at a certain saturation temperature. The interface is assumed to be flat and shear free and the condensation-induced velocity is assumed to be negligibly small compared with radial interface velocity. Finite-difference method is used to slove the nondimensional form of steady-state continuity, momentum, and energy equations. Calculations are conducted for jet Reynolds numbers ranging from 150 to 600 and Prandtl numbers ranging from 0.85 to 2.65. The effects of previously stated parameters on the condensation Nusselt and Stanton numbers that characterize the steady-state interface condensation process are investigated. Detailed analysis is performed to gain a better understanding of the fundamentals of fluid mixing and interface condensation.

Lin, Chin-Shun↗

NASA NTRS1985

Seyfert galaxy narrow-line regions. II - Kinematic models

A class of kinematic models for the narrow-line regions of active galactic nuclei is presented. The models incorporate continuity-constrained radial flow of emitting material in a bounded, spherical geometry. They are designed to represent the narrow-line regions in as simple a manner as is consistent with current knowledge. The systematic comparison of line profiles arising from the models to the spectra in the forbidden O III lambda 5007 emission line which have been described in Paper I of this series is used as a probe of the line-emitting region kinematics: the model parameter areas of interest are identified and tested for consistency with the data. The results indicate heterogeneous kinematic conditions; the most common pattern is outflow of emitting material in a radially decelerating velocity field in the presence of distributed obscuration. However, some observed line profiles can be fitted by several model profiles from very different kinematic conditions, indicating that the information in a spatially unresolved line profile is insufficient to constrain uniquely the geometry and kinematics of the line-emitting region. Although the specific conclusions are model dependent, a predominantly radial pattern of velocities and a distribution of obscuring material are probably essential features of any successful kinematic model of the narrow-line regions.

Vrtilek, J. M.↗

NASA NTRS1986

Influence of large-scale motion on turbulent transport for confined coaxial jets. Volume 2: Navier-Stokes calculations of swirling and nonswirling confined coaxial jets

The existence of large scale coherent structures in turbulent shear flows has been well documented. Discrepancies between experimental and computational data suggest a necessity to understand the roles they play in mass and momentum transport. Using conditional sampling and averaging on coincident two-component velocity and concentration velocity experimental data for swirling and nonswirling coaxial jets, triggers for identifying the structures were examined. Concentration fluctuation was found to be an adequate trigger or indicator for the concentration-velocity data, but no suitable detector was located for the two-component velocity data. The large scale structures are found in the region where the largest discrepancies exist between model and experiment. The traditional gradient transport model does not fit in this region as a result of these structures. The large scale motion was found to be responsible for a large percentage of the axial mass transport. The large scale structures were found to convect downstream at approximately the mean velocity of the overall flow in the axial direction. The radial mean velocity of the structures was found to be substantially greater than that of the overall flow.

Weinberg, B. C.↗

NASA NTRS1986

Influence of large-scale motion on turbulent transport for confined coaxial jets. Volume 1: Analytical analysis of the experimental data using conditional sampling

The existence of large scale coherent structures in turbulent shear flows has been well documented. Discrepancies between experimental and computational data suggest a necessity to understand the roles they play in mass and momentum transport. Using conditional sampling and averaging on coincident two component velocity and concentration velocity experimental data for swirling and nonswirling coaxial jets, triggers for identifying the structures were examined. Concentration fluctuation was found to be an adequate trigger or indicator for the concentration-velocity data, but no suitable detector was located for the two component velocity data. The large scale structures are found in the region where the largest discrepancies exist between model and experiment. The traditional gradient transport model does not fit in this region as a result of these structures. The large scale motion was found to be responsible for a large percentage downstream at approximately the mean velocity of the overall flow in the axial direction. The radial mean velocity of the structures was found to be substantially greater than that of the overall flow.

Brondum, D. C.↗

NASA NTRS1978

Boundary-value problem for a counterrotating electrical discharge in an axial magnetic field

An electrical discharge between two ring electrodes embedded in the mantle of a cylindrical chamber is considered, in which the plasma in the anode and cathode regions rotates in opposite directions under the influence of an external axial magnetic field. The associated boundary-value problem for the coupled partial differential equations describing the azimuthal velocity and radial current-density fields is solved in closed form. The velocity, current density, induced magnetic induction, and electric fields are presented for typical Hartmann numbers, magnetic Reynolds numbers, and geometry parameters. The discharge is shown to produce anodic and cathodic plasma sections rotating at speeds of the order 1,000,000 cm/sec for conventional magnetic field intensities. Possible application of the magnetoactive discharge as a plasma centrifuge for isotope separation is discussed.

Hong, S. H.↗

NASA NTRS1994

A Combined Experimental/Computational Study of Flow in Turbine Blade Cooling Passage

Laser velocimetry was utilized to map the velocity field in a serpentine turbine blade cooling passage at Reynolds and Rotation numbers of up to 25.000 and 0.48. These results were used to assess the combined influence of passage curvature and Coriolis force on the secondary velocity field generated. A Navier-Stokes code (NASTAR) was validated against incompressible test data and then used to simulate the effect of buoyancy. The measurements show a net convection from the low pressure surface to high pressure surface. The interaction of the secondary flows induced by the turns and rotation produces swirl at the turns, which persisted beyond 2 hydraulic diameters downstream of the turns. The incompressible flow field predictions agree well with the measured velocities. With radially outward flow, the buoyancy force causes a further increase in velocity on the high pressure surface and a reduction on the low pressure surface. The results were analyzed in relation to the heat transfer measurements of Wagner et al. (1991). Predicted heat transfer is enhanced on the high pressure surfaces and in turns. The incompressible flow simulation underpredicts heat transfer in these locations. Improvements observed in compressible flow simulation indicate that the buoyancy force may be important.

Tse, D. G. N.↗

NASA NTRS1990

Stellar kinematics of elliptical galaxies in pairs

In both galaxy pairs Arp 166 and 3C 278 the authors find radially increasing velocity dispersions indicating a perturbed, non-equilibrium state of the galaxies after the tidal interaction. In all galaxies, the increase is most pronounced in the regions which correspond to the centers of the outer isophotes. The authors suggest a scenario in which the galaxies are strongly decelerated on their orbits during the encounter. The deceleration depends on the radial position in the perturbed galaxy and vanishes in the center of the perturbed galaxy (Spitzer, 1958). In addition, the crossing time of the stars near the center is very short, implying that the tidal perturbations can be averaged over several orbital periods (e.g., Binney and Tremaine, 1987). In consequence, the central parts are not affected by the tidal interaction while the outer parts are strongly decelerated. This leads to a displacement of the central parts of the galaxies with respect to their envelopes in an anti-symmetrical way for the two components of each galaxy pair. The motions of the central parts subsequently are opposed by dynamical friction with the surrounding envelopes. Due to dynamical friction, the density of the stars increases in the wakes of the moving central parts (Mulder, 1983). The overdensity of stars in the wakes of the moving central parts efficiently decelerates the motions of the central parts. The reaction of the stars in the overdensity regions leads to an increase of the velocity dispersion mainly along the orbits of the moving central parts. The presented observations, especially the asymmetrical luminosity profiles and the radially increasing velocity dispersions support consistently the above scenario of tidal interaction between galaxies. Further spectroscopic observations are necessary in order to investigate the degree of anisotropy in the kinematically perturbed regions.

Madejsky, Rainer↗

NASA NTRS1972

Velocity of the solar wind as determined from interplanetary scintillations.

The method of smooth perturbations is used to derive the equations for interplanetary scintillation in a (statistically) spherically symmetric solar wind with constant wind velocity. The expressions, valid in the limit of small scintillation index, are used to discuss the relation between the radial wind velocity and the observed projected velocity of the scintillation pattern. It is found that the pattern velocity is systematically less than the wind velocity by a substantial fraction, depending on the radial variation of the density fluctuations. If the fluctuations fall off as 1/r-squared the correction is 18 percent, whereas if the fluctuations are proportional to 1/r the correction is 57 percent. The effects may be even more severe if the solar wind is not spherically symmetric.

Jokipii, J. R.↗