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At least 1,225 records · Page 68
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Calculation procedures for potential and viscous flow solutions for engine inlets

The method and basic elements of computer solutions for both potential flow and viscous flow calculations for engine inlets are described. The procedure is applicable to subsonic conventional (CTOL), short-haul (STOL), and vertical takeoff (VTOL) aircraft engine nacelles operating in a compressible viscous flow. The calculated results compare well with measured surface pressure distributions for a number of model inlets. The paper discusses the uses of the program in both the design and analysis of engine inlets, with several examples given for VTOL lift fans, acoustic splitters, and for STOL engine nacelles. Several test support applications are also given.

Albers, J. A.↗
NASA NTRS1972

Deformed Brueckner-Hartree-Fock calculations.

The renormalized Brueckner-Hartree-Fock (RBHF) theory for many-body nuclear systems has been generalized to permit calculations for intrinsic states having permanent deformation. Both Hartree-Fock and Brueckner self-consistencies are satisfied, and details of the numerical techniques are discussed. The Hamada-Johnston interaction is used in a study of deformations, binding, size, and separation energies for several nuclei. Electromagnetic transition rates, moments, and electron scattering form factors are calculated using nuclear wave functions obtained by angular momentum projection. Comparison is made to experiment as well as to predictions of ordinary and density-dependent Hartree-Fock theory.

Ford, W. F.↗
NASA NTRS1972

Population inversion calculations using near resonant charge exchange as a pumping mechanism.

A theoretical study is conducted to investigate the possibility of obtaining inversions in a plasma of metals such as Mg, Ca, Sr, or Ba by charge exchange with inert gas ions. The gases considered include He, Ne, Xe, Ar, or N. The analysis uses rate equations to calculate the density of the various ion levels and an energy equation to calculate the electron temperature. Both charge exchange and electron collisional excitation of the various ion levels are considered.

Chubb, D. L.↗
NASA NTRS1972

Calculation of 5250.216 A line profiles in sunspots.

It is shown that spectral line profiles, used in the calibration and interpretation of magnetograph results, cannot be considered as reliable when they are calculated under the assumption of pure absorption and local thermodynamic equilibrium, frequently employed. Because of this assumption, the line-to-continuous absorption ratio becomes very large at the top of the sunspot model, causing the emergent intensity to originate at a very shallow depth in the sunspot. This is illustrated by calculations of the Fe I 5250.2 A line for three sunspot models.

Dunn, A. R.↗
NASA NTRS1973

Precise calculation of the magnetosphere surface for a tilted dipole.

The shape of the magnetosphere has been calculated self-consistently for inclinations of the earth's magnetic dipole from perpendicular to the solar wind. Inclination angles of 0-35 deg have been chosen in steps of 5 deg and various smooth trends in the surface characteristics with increasing inclination angle noted. The surface points and the complete field at the surface points have been calculated for the entire surfaces. The neutral point region has been given precise study in one degree steps and is found to be tangent to the solar wind velocity and to have a smooth continuous curvature.

Choe, J. Y.↗
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 NTRS1973

A biased model for calculating the evolution in solar absorptance.

A biased model is proposed to account for the smooth curve type of degradation experienced by spacecraft environmental interfacing materials. Because the space environment is nondestructive, the solar absorptance (alpha) must reach its maximum value in finite time, monotonically, without inflection points and be single valued, viz., alpha equals alpha-zero plus (Bt - D) exp (-At). A simple procedure is also included for the parametric calculation of A, B, and D with respect to solar intensity, particle flux, and temperature. The suitability of the model is discussed with regard to destructive testing, and a more general equation proposed. Use of the model for alpha calculations appropriate to the HELIOS missions is outlined.

Schutt, J. B.↗
NASA NTRS1973

Tektite ablation - Some confirming calculations.

The calculation of tektite ablation has been redone, taking into account transient effects, internal radiation, melting and nonequilibrium vaporization of the glass, and the drag effect of the flanges. It is found that the results confirm the earlier calculations of Chapman and his group and of Adams and his co-workers. The general trend of the results is not sensitive to reasonable changes of the physical parameters. The ablation is predominantly by melting rather than by vaporization at all velocities up to 11 km/sec; this is surprising in view of the lack of detectable melt flow in most tektites. Chemical effects have not been considered.

O'Keefe, J. A., III↗
NASA NTRS1973

Detailed balance as a check on impact parameter calculations.

It is demonstrated numerically that detailed balance indeed is well satisfied in the multi-state impact parameter formulation of proton-hydrogen atom collisions. It is also demonstrated numerically that detailed balance is a much more sensitive test of computational accuracy than is the charge conservation test usually employed in such impact parameter calculations. It is suggested that detailed balance be used as a check on all impact parameter calculations. That even agreement with detailed balance may not be a sufficient test for accuracy of the results is pointed out.

Tai, H.↗
NASA NTRS1973

A new method for calculating correction factors for near-field gain measurements.

A new method is demonstrated with which near-field antenna gain correction factors can be calculated directly from measured far-field pattern data by using a spherical wave expansion of the pattern. This eliminates the need for any assumptions regarding antenna aperture field distributions. For illustration, the method is applied to the case of a horn antenna. A comparison of the calculation results with direct measurement data shows an agreement within 0.03 dB. The method, when compared to the method used by Chu and Semplak (1965), is found to show similar agreement.

Ludwig, A. C.↗
NASA NTRS1973

A computer program to calculate zeroes, extrema, and interval integrals for the associated Legendre functions

A computer program is described for the calculation of the zeroes of the associated Legendre functions, Pnm, and their derivatives, for the calculation of the extrema of Pnm and also the integral between pairs of successive zeroes. The program has been run for all n,m from (0,0) to (20,20) and selected cases beyond that for n up to 40. Up to (20,20), the program (written in double precision) retains nearly full accuracy, and indications are that up to (40,40) there is still sufficient precision (4-5 decimal digits for a 54-bit mantissa) for estimation of various bounds and errors involved in geopotential modelling, the purpose for which the program was written.

Payne, M. H.↗
NASA NTRS1973

A computer program for calculating the perfect gas inviscid flow field about blunt axisymmetric bodies at an angle of attack of 0 deg

A method for the rapid calculation of the inviscid shock layer about blunt axisymmetric bodies at an angle of attack of 0 deg has been developed. The procedure is of an inverse nature, that is, a shock wave is assumed and calculations proceed along rays normal to the shock. The solution is iterated until the given body is computed. The flow field solution procedure is programed at the Langley Research Center for the Control Data 6600 computer. The geometries specified in the program are sphores, ellipsoids, paraboloids, and hyperboloids which may conical afterbodies. The normal momentum equation is replaced with an approximate algebraic expression. This simplification significantly reduces machine computation time. Comparisons of the present results with shock shapes and surface pressure distributions obtained by the more exact methods indicate that the program provides reasonably accurate results for smooth bodies in axisymmetric flow. However, further research is required to establish the proper approximate form of the normal momentum equation for the two-dimensional case.

Zoby, E. V.↗
NASA NTRS1973

Calculation of eddy viscosity in a compressible turbulent boundary layer with mass injection and chemical reaction, volume 2

As described in Vol. 1, the eddy viscosity is calculated through the turbulent kinetic energy, in order to include the history of the flow and the effect of chemical reaction on boundary layer characteristics. Calculations can be performed for two different cooling concepts; that is, transpiration and regeneratively cooled wall cases. For the regenerative cooling option, coolant and gas side wall temperature and coolant bulk temperature in a rocket engine can be computed along the nozzle axis. Thus, this computer program is useful in designing coolant flow rate and cooling tube geometry, including the tube wall thickness as well as in predicting the effects of boundary layers along the gas side wall on thrust performances.

Omori, S.↗
NASA NTRS1973

A radiation model for calculating atmospheric corrections to remotely sensed infrared measurements, version 2

A numerical model is developed which calculates the atmospheric corrections to infrared radiometric measurements due to absorption and emission by water vapor, carbon dioxide, and ozone. The corrections due to aerosols are not accounted for. The transmissions functions for water vapor, carbon dioxide, and water are given. The model requires as input the vertical distribution of temperature and water vapor as determined by a standard radiosonde. The vertical distribution of carbon dioxide is assumed to be constant. The vertical distribution of ozone is an average of observed values. The model also requires as input the spectral response function of the radiometer and the nadir angle at which the measurements were made. A listing of the FORTRAN program is given with details for its use and examples of input and output listings. Calculations for four model atmospheres are presented.

Boudreau, R. D.↗
NASA NTRS1974

Recommended radiative property data for Venusian entry calculations

A compilation of experimental and calculated data on the radiative properties species important in Venusian entry is presented. Molecular band systems, atomic lines, free-bound, and free-free continua are considered for the principal radiating species of shock heated carbon dioxide. A limited amount of data pertinent to the species in the ablation layer is also included. The assumption is made that the Venus atmosphere so closely approximates pure CO2 that the inviscid layer radiation is due almost entirely to thermally excited CO2. The only exception is the inclusion of data on the Violet band system of CN. Recommendations are made as to best property values for radiative heating calculations. A review of the basic equations and the relationships of the various emission-absorption gas porperties is also included.

Jones, J. J.↗
NASA NTRS1974

X-alpha calculation of transition energies in multiply ionized atoms

It is shown that the accuracy of calculations can be improved if appropriate (different) values of alpha are used for each configuration. Alternatively, the Slater Transition state can be used, wherein a total energy difference is related to a difference in single electron eigenvalues. By a series expansion, the value of alpha for an excited configuration can be related to its value for the ground state configuration. The terms Delta alpha (delta Epsilon/delta alpha) exhibit a similar dependence on atomic number as the ground state values of alpha. Results of sample calculations are reported and compared with experiment.

Ringers, D. A.↗
NASA NTRS1974

Spectral irradiance curve calculations for any type of solar eclipse

A simple procedure is described for calculating the eclipse function (EF), alpha, and hence the spectral irradiance curve (SIC), (1-alpha), for any type of solar eclipse: namely, the occultation (partial/total) eclipse and the transit (partial/annular) eclipse. The SIC (or the EF) gives the variation of the amount (or the loss) of solar radiation of a given wavelength reaching a distant observer for various positions of the moon across the sun. The scheme is based on the theory of light curves of eclipsing binaries, the results of which are tabulated in Merrill's Tables, and is valid for all wavelengths for which the solar limb-darkening obeys the cosine law: J = sub c (1 - X + X cost gamma). As an example of computing the SIC for an occultation eclipse which may be total, the calculations for the March 7, 1970, eclipse are described in detail.

Deepak, A.↗
NASA NTRS1974

Calculation of the total electron excitation cross section in the Born approximation using Slater wave functions for the Li (2s yields 2p), Li (2s yields 3p), Na (3s yields 4p), Mg (3p yields 4s), Ca (4s yields 4p) and K (4s yields 4p) excitations

Excitation of neutral atoms by inelastic scattering of incident electrons in gaseous nebulae were investigated using Slater Wave functions to describe the initial and final states of the atom. Total cross sections using the Born Approximation are calculated for: Li(2s yields 2p), Na(3s yields 4p), k(4s yields 4p). The intensity of emitted radiation from gaseous nebulae is also calculated, and Maxwell distribution is employed to average the kinetic energy of electrons.

Simsic, P. L.↗