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At least 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
NASA NTRS1963

Lunar Flight Study Series: Volume 6. A Study of Geometrical and Terminal Characteristics of Earth-Moon Transits Embedded in the Earth-Moon Plane

This report represents the results of a study of coplanar earth-moon transits. The study was initiated to provide information concerning coplanar geometrical characteristics of earth-moon trnasits. The geometrical aspects of transit behavior are related to variations injection conditions. The model of the earth-moon system used in this investigation is the Jacobian model of the restricted three body problem. All transits considered in this study are restricted to the moon-earth plane (MEP).

TRAJECTORY MEASURING SYSTEM↗
NASA NTRS1971

Radioactive transitions in the helium isoelectronic sequence

The principles of the atomic spectrum theory are used to quantitatively analyze radiation transitions in two-electron helium-like atomic systems. Quantum theoretical methods, describing absorption and emission of a single photon in a radiative transition between two stationary states of an atomic system, reproduced the energy level diagram for the low lying states of helium. Reliable values are obtained from accurate variationally determined two-electron nonrelativistic wave functions for radiative transition probabilities of 2 3p states in the helium isoelectric sequence, and for the 2 1s and 2 3s1 states of the helium sequence.

Dalgarno, A.↗
NASA NTRS1972

Medium-to-medium transition radiation and the detection of ultrarelativistic charged particles

The use of X-ray transition radiation to distinguish between protons and positrons of equal rigidity was investigated. A formula for the transition radiation spectrum from a medium-to-medium boundary was derived. The formation zone effect was found to limit the detection of transition radiation from ultrarelativistic particles. Curves showing the results of the spectrum calculations are presented.

Robbins, D. E.↗
NASA NTRS1972

Investigation of low-Z Coster-Kronig transitions by means of Auger and photoelectron spectroscopy

Experimental intensity ratios of Auger transitions for Co, Ni, Cu, and Zn as well as the relative L sub 2 and L sub 3 level widths of Cu and Zn, derived from their photoelectron spectra, are presented. Evidence is presented that a great deal of vacancy reorganization took place following photoionization and prior to Auger emission. These reorganizations are assumed to be due to Coster-Kronig transitions f sub 23. These results are compared with theoretical calculations and agree with predicted discontinuity at Z = 30 where f sub 23 transitions become energetically impossible.

Yin, L. I.↗
NASA NTRS1972

Effects of wall cooling and angle of attack on boundary layer transition on sharp cones at free stream Mach 7.4

Tests were conducted on 5 deg and 15 deg half-angle sharp cones at wall-to-total-temperature ratios of 0.08 to 0.4, and angles of attack from 0 deg to 20 deg. The results indicate that (1) transition Reynolds numbers decrease with decreasing temperature ratio, (2) local transition Reynolds numbers decrease from the windward to the leeward side of the model, and (3) transition data on the windward ray of cones can be correlated in terms of the crossflow velocity gradient, momentum thickness Reynolds number, local Mach number, and cone half-angle.

Mateer, G. G.↗
NASA NTRS1971

Hypersonic boundary-layer transition in the presence of wind-tunnel noise.

Description of additional results indicating that a unique relationship exists between rms sound pressure level and transition Reynolds number, provided all other parameters are held nearly invariant. The results illustrate the different levels of the transition Reynolds numbers obtained in six facilities with nearly invariant laminar boundary layers on the different models (at the same local unit Reynolds number) and indicate that some facility characteristic has a strong influence on the transition Reynolds numbers.

Stainback, P. C.↗
NASA NTRS1972

Effect of mass-addition distribution and injectant on heat transfer and transition criteria.

Surface pressures, heat-transfer rates, and transition locations for a sharp cone (whose semivertex angle is 12 deg) were obtained in a hypervelocity wind tunnel at a free-stream Mach number of 12 and a free-stream Re/ft range of 3,000,000 to 6,000,000. The effects of injecting either methane, nitrogen, or Freon-22 (at rates up to 2.1% of free-stream rate) were studied for a uniform injection-distribution and for a variable injection-distribution. Gaseous injection had little effect on the surface pressure measurements. For a given mass injection distribution, the laminar region heat-transfer decreases as the injection rate increases or as the molecular weight of the injectant decreases. For a given mass-injection rate (integrated over the surface of the entire cone), the transition location and heat-transfer rates were sensitive to the injection distribution. The transition Reynolds numbers were significantly greater when the local injection rate was constant over the surface of the cone.

Bertin, J. J.↗
NASA NTRS1971

Semiclassical vibration-rotation transition probabilities for motion in molecular state averaged potentials.

Collision-induced vibration-rotation transition probabilities are calculated from a semiclassical three-dimensional model, in which the collision trajectory is determined by the classical motion in the interaction potential that is averaged over the molecular rotational state, and compared with those for which the motion is governed by a spherically averaged potential. For molecules that are in highly excited rotational states, thus dominating the vibrational relaxation rate at high temperature, it is found that the transition probability for rotational state averaging is smaller than that for spherical averaging. For typical collisions, the transition cross section is decreased by a factor of about 1.5 to 2.

Stallcop, J. R.↗
NASA NTRS1972

Power series evaluation of transition and covariance matrices.

Reexamination power series solutions to the matrix covariance differential equation and the transition differential equation. Truncation error bounds are derived which are computationally attractive and which extend previous results. Polynomial approximations are obtained by exploiting the functional equations satisfied by the transition and covariance matrices. The series-functional equation propagation technique represents a fast and accurate alternative to the numerical integration of the time-invariant transition and covariance equations.

Bierman, G. J.↗
NASA NTRS1972

Anisotropic ultrahigh gain emission observed in rotational transitions in optically pumped HF gas.

Gain and laser oscillations are obtained on rotational transitions of the first excited vibrational state of HF gas at room temperature, resonantly pumped by the 2.7-micron lines of a pulsed HF laser. Pumping the P-branch transitions connecting the ground and first excited vibrational states produces gain at the coupled rotational transitions at 36, 42, 51, 63, 84, and 126 microns. The gain exhibits directional properties characteristic of a unidirectional amplifier predicted by a recent theory. The incremental gains of these lines are very large, in excess of 1/cm, and the lines oscillate easily without mirrors (superradiance).

Skribanowitz, N.↗
NASA NTRS1972

Transition radiation as a source of cosmic X-rays.

It is shown that transition radiation generated during the passage of relativistic charged particles through interstellar grains can be an important source of cosmic X-rays. In order to account for recent X-ray observations below 300 eV by transition radiation, an energy density in interstellar space of about 10 eV per cu cm in 10 MeV electrons is required. This seems to rule out transition radiation as an important source of diffuse cosmic X-rays in any energy region.

Ramaty, R.↗
NASA NTRS1972

Cone transitional boundary-layer structure at Me = 14.

Experimental results suggest that the boundary-layer mean profiles in hypersonic flows may be highly transitional in the outer part of the boundary layer before the transition process is detected at the surface. Means of determining the initial location where the transition process begins in the outer part of the boundary layer are considered.

Fischer, M. C.↗
NASA NTRS1972

Transition in compressible free shear layers.

The transition Reynolds number for shear layers produced by interactions between weak and strong shock waves is determined on the basis of experiments performed in a 20-in. (Mach 6) and an 11-in. (Mach 6.9) hypersonic tunnel. A variable angle wedge was used to generate a planar shock wave which interacted with the bow wave of a blunt body. An average value of the transition length (defined as the length along the shear layer from the shock interaction to the point where turbulence became visible on schlieren photographs) was used to determine the transition Reynolds number.

Birch, S. F.↗
NASA NTRS1972

Free flight determination of boundary layer transition on small scale cones in the presence of surface ablation

To assess the possibility of achieving extensive laminar flow on conical vehicles during hyperbolic entry, the Ames Research Center has had an ongoing program to study boundary-layer transition on ablating cones. Boundary layer transition results are presented from ballistic range experiments with models that ablated at dimensionless mass transfer rates comparable to those expected for full scale flight at speeds up to 17 km/sec. It was found possible to measure the surface recession and hence more accurately identify regions of laminar, transitional, and turbulent flow along generators of the recovered cones. Some preliminary results using this technique are presented.

Wilkins, M. E.↗
NASA NTRS1973

Calculation of transitional boundary-layer flows.

The results of a finite-difference calculation of hypersonic transitional boundary-layer flow are presented. Precursor-transition and low Reynolds number turbulence effects are included. These calculation results are compared with data from a source where profiles are available at the beginning, middle and end of the hypersonic transitional flow. The results indicate that the low Reynolds number effect is the most important.

Bushnell, D. M.↗
NASA NTRS1974

An experimental investigation of wall boundary layer transition Reynolds numbers in an expansion tube

Experimental measurements of boundary-layer transition in an expansion-tube test-gas flow are presented along with radial distributions of pitot pressure. An integral method for calculating constant Reynolds number lines for an expansion-tube flow is introduced. Comparison of experimental data and constant Reynolds number calculations has shown that for given conditions, wall boundary-layer transition occurs at a constant Reynolds number in an expansion-tube flow. Operating conditions in the expansion tube were chosen so that the effects of test-gas nonequilibrium on boundary-layer transition could be studied.

Weilmuenster, K. J.↗
NASA NTRS1974

Wind tunnel experiments relating to supersonic and hypersonic boundary layer transition

Hot-wire anemometry is used to study the origin and growth of 'natural' fluctuations in zero pressure gradient boundary layers and the location of transition to turbulence for several Mach numbers between 1.6 and 8.5. The importance to transition of certain physical mechanisms is examined through comparison of the fluctuation growth with the sound-forcing and stability theories of Mack. The mechanisms are shown to assume varying importance in low supersonic, high supersonic and hypersonic regimes. The effect on transition of cone angle of attack, tip heating, and model vibration is mentioned.

Kendall, J. M.↗
NASA NTRS1974

Aluminum oxide in stellar spectra - An infrared electronic transition

Review of recent research on the possibility of detecting the infrared electronic transition of aluminum oxide in the spectra of cool stars. It is shown that this transition may be of considerable significance for the study of Mira-type variables. Specific targets of further laboratory investigation of the transition are pointed out.

Luck, R. E.↗