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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Effect of initial tangential velocity distribution on the mean evolution of a swirling turbulent free jet

An existing cold jet facility at NASA-Lewis was modified to produce swirling flows with controllable initial tangential velocity distribution. Distinctly different swirl velocity profiles were produced, and their effects on jet mixing characteristics were measured downstream of an 11.43 cm diameter convergent nozzle. It was experimentally shown that in the near field of a swirling turbulent jet, the mean velocity field strongly depends on the initial swirl profile. Two extreme tangential velocity distributions were produced. The two jets shared approximately the same initial mass flow rate of 5.9 kg/s, mass averaged axial Mach number and swirl number. Mean centerline velocity decay characteristics of the solid body rotation jet flow exhibited classical decay features of a swirling jet with S = 0.48 reported in the literature. It is concluded that the integrated swirl effect, reflected in the swirl number, is inadequate in describing the mean swirling jet behavior in the near field.

Farokhi, S.↗
NASA NTRS1988

Effect of initial tangential velocity distribution on the mean evolution of a swirling turbulent free jet

An existing cold jet facility at NASA-Lewis was modified to produce swirling flows with controllable initial tangential velocity distribution. Distinctly different swirl velocity profiles were produced, and their effects on jet mixing characteristics were measured downstream of an 11.43 cm diameter convergent nozzle. It was experimentally shown that in the near field of a swirling turbulent jet, the mean velocity field strongly depends on the initial swirl profile. Two extreme tangential velocity distributions were produced. The two jets shared approximately the same initial mass flow rate of 5.9 kg/s, mass averaged axial Mach number and swirl number. Mean centerline velocity decay characteristics of the solid body rotation jet flow exhibited classical decay features of a swirling jet with S = 0.48 reported in the literature. It is concluded that the integrated swirl effect, reflected in the swirl number, is inadequate in describing the mean swirling jet behavior in the near field.

Farokhi, S.↗
NASA NTRS2010

Whistler Waves Driven by Anisotropic Strahl Velocity Distributions: Cluster Observations

Observed properties of the strahl using high resolution 3D electron velocity distribution data obtained from the Cluster/PEACE experiment are used to investigate its linear stability. An automated method to isolate the strahl is used to allow its moments to be computed independent of the solar wind core+halo. Results show that the strahl can have a high temperature anisotropy (T(perpindicular)/T(parallell) approximately > 2). This anisotropy is shown to be an important free energy source for the excitation of high frequency whistler waves. The analysis suggests that the resultant whistler waves are strong enough to regulate the electron velocity distributions in the solar wind through pitch-angle scattering

Vinas, A.F.↗
NASA NTRS1993

Velocity distributions of hydrogen atoms and hydroxyl radicals produced through solar photodissociation of water

The velocity distributions of H and OH fragments produced through solar photodissociation of gaseous H2O molecules under collisionless conditions are presented. The calculations are carried out using: the most recently available absolute partial cross sections for the production of H and OH through photodissociation of H2O from its absorption onset at 1860 A down to 500 A; the newly available vibrational and rotational energy distributions of both the excited and ground state OH photofragments; the calculated cross sections for the total dissociation processes; and the integrated solar flux in 10 A increments from 500 to 1860 A in the continuum regions and the specific wavelength and flux at the bright solar lines. The calculated results show that the H atoms and the OH radicals produced exhibit multiple velocity groups. Since most current cometary modeling uses a single velocity of 20 km/sec associated with the photodissociation of H2O, the present results may be useful in interpreting the many peaks observed in the velocity distributions of the H Lyman alpha and H alpha of comets.

Wu, C. Y. R.↗
NASA NTRS1947

Isolated and cascade airfoils with prescribed velocity distribution

An exact solution of the problem of designing an airfoil with a prescribed velocity distribution on the suction surface in a given uniform flow of an incompressible perfect fluid is obtained by replacing the boundary of the airfoil by vortices. By this device, a method of solution is developed that is applicable both to isolated airfoils and to airfoils in cascade. The conformal transformation of the designed airfoil into a circle can then be obtained and the velocity distribution at any angle of attack computed. Numerical illustrations of the method are given for the airfoil in cascade.

Goldstein, Arthur W↗
NASA NTRS1991

Initial drop size and velocity distributions for airblast coaxial atomizers

Phase Doppler measurements were used to determine initial drop size and velocity distributions after a complete disintegration of coaxial liquid jets. The Sauter mean diameter (SMD) distribution was found to be strongly affected by the structure and behavior of the preceding liquid intact jet. The axial measurement stations were determined from the photographs of the coaxial liquid jet at very short distances (1-2 mm) downstream of the observed break-up locations. Minimum droplet mean velocities were found at the center, and maximum velocities were near the spray boundary. Size-velocity correlations show that the velocity of larger drops did not change with drop size. Drop rms velocity distributions have double peaks whose radial positions coincide with the maximum mean velocity gradients.

Eroglu, H.↗
NASA NTRS1992

Velocity distribution of fragments of catastrophic impacts

Three dimensional velocities of fragments produced by laboratory impact experiments were measured for basalts and pyrophyllites. The velocity distribution of fragments obtained shows that the velocity range of the major fragments is rather narrow, at most within a factor of 3 and that no clear dependence of velocity on the fragment mass is observed. The NonDimensional Impact Stress (NDIS) defined by Mizutani et al. (1990) is found to be an appropriate scaling parameter to describe the overall fragment velocity as well as the antipodal velocity.

Takagi, Yasuhiko↗
NASA NTRS2004

Pickup Ion Velocity Distributions at Titan: Effects of Spatial Gradients

The principle source of pickup ions at Titan is its neutral exosphere, extending well above the ionopause into the magnetosphere of Saturn or the solar wind, depending on the moon's orbital position. Thermal and nonthermal processes in the thermosphere generate the distribution of neutral atoms and molecules in the exosphere. The combination of these processes and the range of mass numbers, 1 to over 28, contribute to an exospheric source structure that produces pickup ions with gyroradii that are much larger or smaller than the corresponding scale heights of their neutral sources. The resulting phase space distributions are dependent on the spatial structure of the exosphere as well as that of the magnetic field and background plasma. When the pickup ion gyroradius is less than the source gas scale height, the pickup ion velocity distribution is characterized by a sharp cutoff near the maximum speed, which is twice that of the ambient plasma times the sine of the angle between the magnetic field and the flow velocity. This was the case for pickup H(sup +) ions identified during the Voyager 1 flyby. In contrast, as the gyroradius becomes much larger than the scale height, the peak of the velocity distribution in the source region recedes from the maximum speed. Iri addition, the amplitude of the distribution near the maximum speed decreases. These more beam like distributions of heavy ions were not observed from Voyager 1 , but should be observable by more sensitive instruments on future spacecraft, including Cassini. The finite gyroradius effects in the pickup ion velocity distributions are studied by including in the analysis the possible range of spatial structures in the neutral exosphere and background plasma.

Hartle, R. E.↗
NASA NTRS1980

Anisotropic velocity distributions in M87 - Is a supermassive black hole necessary

A collisionless distribution of stars with an anisotropic velocity distribution is considered as a model for the cores of spherical galaxies. The first moment of the corresponding Boltzmann equation is integrated to give the resulting density and velocity dispersion profiles. These distributions plus a central point source of light give a good fit to the data from recent observations of M87 without requiring a supermassive central object. This model requires one less fitting parameter than published models incorporating a central black hole. The same model with no point source of light also provides a good fit to the normal E1 galaxy NGC 3379. The success of this model in describing the cores of both M87 and NGC 3379 suggests that a supermassive black hole is not necessary in either.

Duncan, M. J.↗
NASA NTRS1993

High-velocity tails on the velocity distribution of solar wind ions

Recent observations of the solar wind using the SWICS instrument on the Ulysses spacecraft have shown the presence of high-velocity 'tails' on the velocity distribution of protons. Similar features have also been observed on the velocity distributions of helium and oxygen ions. Of the order of 1 percent of the solar wind density is involved in these tails, which are approximately exponential in shape and persist to V = V(B) + 10V(th) or beyond, where VB is the bulk velocity and V(th) the thermal velocity of the solar wind. This paper contains a preliminary description of the phenomenon. It is clear that it is ultimately connected with the passage of interplanetary shocks past the spacecraft and that particle acceleration at oblique shocks is involved.

Ogilvie, K. W.↗
NASA NTRS1991

Deriving the velocity distribution of meteoroids from the measured meteoroid impact directionality on the various LDEF surfaces

Because of spacecraft motion, a much higher flux of meteoroids is expected to strike the leading (apex) surface of a spacecraft than is expected to strike the trailing (antapex) surface. The ratio of fluxes (apex to antapex) depends on the velocity distribution of meteoroids entering the Earth's atmosphere. The ratio ranges from 5.7 to 9.2 at constant meteoroid mass for the three velocity distributions examined. The velocity of impact is also greater, on average, on the apex surface than on the antapex surface, and the impacts tend to be more normal to the surface. This means that the meteoroids that make a crater of a given diameter are less massive than those that strike the antapex surface. These effects further increase the apex-antapex abundance ratio at constant crater diameter compared to that at constant mass. For craters 100 microns in diameter on 6061 T6 aluminum on the Long Duration Exposure Facility, the ratios obtained on various surfaces are given in tabular form.

Zook, Herbert A.↗
NASA NTRS1978

Measurement of non-Maxwellian electron velocity distributions in a reflex discharge

The results of a ruby laser Thomson scattering study of the space and time-resolved electron velocity distributions in a pulsed Penning discharge in hydrogen are presented. Electron densities were to the order of 10 to the 13th/cu cm and temperatures were roughly 3 eV. This point is just prior to the cessation of the discharge ohmic heating pulse. For magnetic strengths less than 200 G, Maxwellian distributions were found over an energy range six times thermal energy. Temperatures agreed with Langmuir probe data. For fields of 450 G, chaotic plasma potentials were observed to be unstable and the Thomson scattering showed that the electron velocity distributions had central temperatures of 2 eV and wing temperatures of 15-12 eV.

Phipps, C. R., Jr.↗
NASA NTRS1988

On the persistence of unstable bump-on-tail electron velocity distributions in the earth's foreshock

This paper presents further evidence for the persistence of bump-on-tail unstable reduced velocity distributions in the earth's electron foreshock, which contradicts the understanding of quasi-linear saturation of the bump-on-tail instability. A modified theory for the saturation of the bump-on-tail instability in the earth's foreshock is proposed to explain the mechanism of this persistence, and the predictions are compared to the results of a numerical simulation of the electron plasma in the foreshock. The results support the thesis that quasi-linear saturation of the bump-on-tail instability is modified in the foreshock, due to the driven nature of the region, so that at saturation the stabilized velocity distribution still appears bump-on-tail unstable to linear plasma analysis.

Klimas, Alexander J.↗
NASA NTRS1981

On the velocity distribution of ion jets during substorm recovery

The velocity distribution of earthward jetting ions that are observed principally during substorm recovery by satellites at approximately 15-35 earth radii in the magnetotail is quantitatively compared with two different theoretical models - the 'adiabatic deformation' of an initially flowing Maxwellian moving into higher magnetic field strength (model A) and the field-aligned electrostatic acceleration of an initially nonflowing isotropic Maxwellian including adiabatic deformation effects (model B). The assumption is made that the ions are protons or, more generally, that they consist of only one species. It is found that both models can explain the often observed concave-convex shape of isodensity contours of the distribution function.

Birn, J.↗
NASA NTRS1990

Stimulated emission of AKR in regions of a weakly unstable electron velocity distribution

While, according to the cyclotron maser theory, auroral kilometric radiation generates auroral zone instability whose consequent radiation is in many respects consistent with observations, in situ velocity distribution measurements by satellites show only moderate positive gradients which would be only marginally unstable, implying a low radiation level. Numerical simulations are conducted alternatively using an observed electron-velocity distribution and an idealized loss-cone distribution. The expected amplification of X-mode radiation, as well as effects which go beyond the behavior of a simple amplifying medium, emerge in the results.

Kainer, S.↗
NASA NTRS1948

Velocity distributions on two-dimensional wing-duct inlets by conformal mapping

The conformal-mapping method of the Cartesian mapping function is applied to the determination of the velocity distribution on arbitrary two-dimensional duct-inlet shapes such as are used in wing installations. An idealized form of the actual wing-duct inlet is analyzed. The effects of leading edge stagger, inlet-velocity ratio, and section lift coefficients on the velocity distribution are included in the analysis. Numerical examples are given and, in part, compared with experimental data.

Perl, W↗