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At least 541 records · Page 30

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NASA NTRS1974

Development of a method of analysis and computer program for calculating the inviscid flow about the windward surfaces of space shuttle configurations at large angles of attack

A general method developed for the analysis of inviscid hypersonic shock layers is discussed for application to the case of the shuttle vehicle at high (65 deg) angle of attack. The associated extensive subsonic flow region caused convergence difficulties whose resolution is discussed. It is required that the solution be smoother than anticipated.

Maslen, S. H.↗

NASA NTRS1974

Viscous reacting flows with wall slip and catalysis applied to spheres in arc jets and flight

The influence of wall slip and catalytic atom-recombination on the flow field and wall heat flux are calculated for high altitude flight and arc jet flow conditions. Boundary equations, which include velocity slip, temperature jump, and wall catalytic atom recombination, are coupled to the viscous reacting multicomponent Navier-Stokes equations. These equations are solved using a time-dependent finite difference technique applied to spheres in an arc jet flow (Reynolds number of 550) and a high altitude flight case representative of the Space Shuttle Orbiter (Reynolds number of 450). The results indicate that catalysis strongly influences the temperature jump, but not the velocity slip. Slip increases the atom fraction and temperature at both the wall and the flow field. Likewise, the shock stand-off distance, the wall heat flux, and friction coefficient are increased over the nonslip cases. The reacting gas calculations confirm the chemically frozen nature of the shock layer in arc jet flows.

Scott, C. D.↗

NASA NTRS1975

Reflecting heat shields made of microstructured fused silica

Heat sheidls constructed from selected monodisperse distributions of high-purity fused-silica particles are efficient reflectors of visible and near-UV radiation generated in shock-layer of space probe during atmospheric entry.

Congdon, W. M.↗

NASA NTRS1974

Entry aerodynamics and heating

An overview of the problems of entry aerodynamics and heating is given with emphasis on survival of the probe, predictability of performance, and reliability of performance. Technological challenges to performance prediction are considered and include: turbulent heat transfer, radiation blockage, chemical state of the shock layer, afterbody heat transfer, asymmetric ablation, and real-gas aerodynamics. It is indicated that various obstacles must be overcome in order to achieve technology readiness. These obstacles are considered to be: extrapolations from ground tests to flight; lack of flight experience; lack of parametric data; and uncertain knowledge of atmospherics.

Olstad, W.↗

NASA NTRS1974

High purity silica reflecting heat shield development

A reflecting heat shield composed of fused silica in which the scattering results from the refractive index mismatch between silica particles and the voids introduced during the fabrication process is developed. Major considerations and conclusions of the development are: the best material to use is Type A, which is capable of ultra-high-purity and which does not show the 0.243 micrometer absorption band; the reflection efficiency of fused silica is decreased at higher temperatures due to the bathochromic shift of the ultraviolet cut-off; for a given silica material, over the wavelength region and particle sizes tested, the monodisperse particle size configurations produce higher reflectances than continuous particle size configurations; and the smaller monodisperse particle size configurations give higher reflectance than the larger ones. A reflecting silica configuration that is an efficient reflector of shock layer radiation at high ablation temperatures is achieved by tailoring the matrix for optimum scattering and using an ultra-high-purity material.

Congdon, W.↗

NASA NTRS1975

Shock wave structure in an ideal dissociating gas

Composition changes within the shock layer due to chemical reactions are considered. The Lighthill ideal dissociating gas model was used in an effort to describe the oxygen type molecule. First, the two limiting cases, when the chemical reaction rates are very slow and very fast in comparison to local convective rates, are investigated. Then, the problem is solved for arbitrary chemical reaction rates.

Liu, K. H.↗

NASA NTRS1975

Estimates of nonequilibrium radiation for Venus entry

The present investigation is an analysis of the radiation from the chemical nonequilibrium region in the shock layer about a vehicle during Venus entry. The radiation and the flow were assumed to be uncoupled. An inviscid, nonequilibrium flowfield was calculated and an effective electronic temperature was determined for the predominant radiating species. Species concentrations and electronic temperature were then input into a radiation transport code to calculate heating rates. The present results confirm earlier investigations which indicate that the radiation should be calculated using electronic temperatures for the radiating species. These temperatures are not related in a simple way to the local translational temperature. For the described mission, the nonequilibrium radiative heating rate is approximately twice the corresponding equilibrium value at peak heating.

Grose, W. L.↗

NASA NTRS1975

Inviscid supersonic/hypersonic body flowfields and aerodynamics from shock-capturing technique calculations

A shock-capturing, finite-difference computational procedure has been used to predict the body flowfields over a wide range of initial conditions, and these results have been compared with wind tunnel data. Two different studies have been performed. In the first, details of the shock layer surrounding space shuttle orbiter configurations have been calculated. In the second, the aerodynamic forces and moments on a parametrically varied set of blunt biconic bodies of revolution have been evaluated for angles of attack up to 20 degrees and Mach numbers from 5 to 20.

Chaussee, D. S.↗

NASA NTRS1975

Outer planet entry probes aerothermal environment - Status of prediction methodology

A description is given of the computational codes that are to be used in studies of the heating and aerodynamic performance of entry probes for the scientific exploration of the planets Jupiter, Saturn, and Uranus. These codes include a time-asymptotic numerical method which takes into account radiative transport and equilibrium chemistry for the direct solution of the radiative, inviscid flow over an axisymmetric or two-dimensional body. The method considers both supersonic and subsonic flow in the downstream region. Another code represents a laminar, viscous-shock-layer solution.

Sutton, K.↗

NASA NTRS1976

An experimental investigation of supersonic flow past a wedge-cylinder configuration

An experimental investigation of supersonic flow past double-wedge configurations was conducted. Over the range of geometries tested, it was found that, while theoretical solutions both for a Type V pattern and for a Type VI pattern could be generated for a particular flow condition (as defined by the geometry and the free-stream conditions), the weaker, Type VI pattern was observed experimentally. More rigorous flow-field solutions were developed for the flow along the wing leading-edge. Solutions were developed for the three-dimensional flow in the plane of symmetry of a swept cylinder (which represented the wing leading-edge) which was mounted on a wedge (which generated the "bow" shock wave). A numerical code was developed using integral techniques to calculate the flow in the shock layer upstream of the interaction region (i.e., near the wing root). Heat transfer rates were calculated for various free stream conditions. The present investigation was undertaken to examine the effects of crossflow on the resultant flow-field and to verify the flow model used in theoretical calculations.

Barnette, D. W.↗

NASA NTRS1976

Equilibrium and nonequilibrium electron density measurements in transient shock-heated hydrogen-helium plasmas

In the NASA planetary program, atmospheric entry probe missions to Jupiter, Saturn, and Uranus are potential programs now being planned for the 1980's. The work reported in this paper is concerned with predicting the electron density, and resulting radiative emission from the shock layer which must be accommodated by the entry probe heatshield. Within the hydrogen-helium plasma surrounding the forward heatshield, there are regions of near thermochemical equilibrium whose properties are predictable - however, there are uncertainties in these electron density calculations necessitating further measurements by H-beta line broadening and holographic interferometer fringe shift as reported here. There is good agreement between the results obtained from the holographic measurements and the spectroscopic measurements which lends confidence to each of the two completely independent diagnostic techniques. The equilibrium electron density determined from the experimental measurements is somewhat higher than that predicted.

Livingston, F. R.↗

NASA NTRS1975

Series solution for the planar asymmetric blunt-body problem

Accurate semianalytic solutions to the inverse blunt-body problem have been obtained using a method of series expansion. Rational fractions are employed for series summation and analytic continuation. Angles of incidence up to 30 deg and Mach numbers as low as 2 have been considered. The maximum-entropy streamline will not wet the body surface in asymmetric flow. It may pass either above or below the stagnation streamline. Limit lines appear in the supersonic portion of the flow field, both in the shock layer and in its upstream analytic continuation.

Schwartz, L. W.↗

NASA NTRS1976

Accretion onto magnetized neutron stars - Structure and interchange instability of a model magnetosphere

A self-consistent model is analyzed for the spherical infall of weakly magnetized plasma into the magnetosphere of a slowly rotating, strongly magnetized neutron star. It is shown that spherical infall is probably a good approximation for X-ray sources which accrete from a stellar wind. The location of the standoff shock which halts the hypersonic infall is estimated along with the emission from the shocked layer. The location of the equilibrium magnetopause and the structure of the magnetic field within it are calculated; it is found that the magnetic poles are true cusps and that the entry of gas due to equilibrium flow across a cusp is almost certainly dominated by the interchange instability near the magnetic equator. The energy principle is applied to derive necessary conditions for the occurrence of this instability. The results indicate that the strong magnetic-pressure gradient stabilizes the gas unless moderately strong radiative cooling takes place and that the cooled plasma enters the magnetosphere as long filaments capable of moving between field lines. The rate at which the equilibrium magnetopause can 'absorb' mass and momentum is derived, the validity of the approximations employed is discussed, and the likely evolution of the sinking filaments is outlined to show that the spatial distribution of the plasma is determined mainly by the dynamics and thermodynamics of the filaments rather than the magnetic-field structure.

Arons, J.↗

NASA NTRS1977

Apparatus for experimental investigation of aerodynamic radiation with absorption by ablation products

A description is given and calibration procedures are presented for an apparatus that is used to simulate aerodynamic radiant heating during planetary entry. The primary function of the apparatus is to simulate the spectral distribution of shock layer radiation and to determine absorption effects of simulated ablation products which are injected into the stagnation region flow field. An electric arc heater is used to heat gas mixtures that represent the planetary atmospheres of interest. Spectral measurements are made with a vacuum ultraviolet scanning monochromator.

Wells, W. L.↗

NASA NTRS1976

High-velocity interstellar clouds

Interstellar absorption line studies have revealed that rapidly moving clouds within one kiloparsec of the sun have considerably less depletion of heavy elements than in the low-velocity diffuse clouds, and their density is somewhat greater and their thickness smaller. Evaporation of interstellar grains, resulting from grain-grain collisions in interstellar shocks, may provide a possible explanation for the observations. Some problems involved in this mechanism are discussed, particularly the likely dominant importance of the interstellar magnetic field in confining the grains within the shocked layer and in accelerating them through the associated electric field, thus offsetting the frictional force of the gas.

Spitzer, L.↗

NASA NTRS1977

A study of the aerothermal environment for the Pioneer Venus multiprobe mission

In December 1978, four Pioneer Venus probe spacecraft are scheduled for almost simultaneous entry into the Venusian atmosphere at widely dispersed points about the planet. In this study, both detailed and approximate flow field analyses are used to define the entry aerothermal environment for the forebody of each of the four probes. The results show that approximate analyses can be used to predict inviscid radiative and laminar convective heating rates with acceptable accuracy. However, the radiative heating rates obtained with inviscid analyses are significantly greater than those obtained with a nonablating viscous-shock-layer (VSL) analysis, because the VSL analysis includes a strongly absorbing boundary layer. Also, the results show that the radiative heating is sensitive to small variations in atmospheric gas composition while the convective heating is not affected. With carbon-phenolic injection, the convective heating is reduced substantially while the overall radiative heating reduction is very small. Most of the radiative blockage occurs in the atomic line transitions which is significant only in the stagnation region.

Moss, J. N.↗

NASA NTRS1977

Low Reynolds number flow past a blunt axisymmetric body at angle of attack

Low Reynolds number flow of an ideal gas over a blunt axisymmetric body of large half-angle at small angles of attack is investigated, for the case of laminar hypersonic flow. Time-varying viscous shock layer equations describing the flowfield are obtained from the full Navier-Stokes system by keeping terms to second order in the inverse square root of Re in both viscous and inviscid regions; the equations are valid for moderate to high Re. Drag, skin friction, and heating rates were obtained at small (or zero) angles of attack. Conditions experienced by planetary entry probes during the high-altitude (early) legs of an atmospheric entry trajectory are pertinent to the problem.

Kumar, A.↗

NASA NTRS1978

Solution of axisymmetric and two-dimensional inviscid flow over blunt bodies by the method of lines

Comparisons with experimental data and the results of other computational methods demonstrated that very accurate solutions can be obtained by using relatively few lines with the method of lines approach. This method is semidiscrete and has relatively low core storage requirements as compared with fully discrete methods since very little data were stored across the shock layer. This feature is very attractive for three dimensional problems because it enables computer storage requirements to be reduced by approximately an order of magnitude. In the present study it was found that nine lines was a practical upper limit for two dimensional and axisymmetric problems. This condition limits application of the method to smooth body geometries where relatively few lines would be adequate to describe changes in the flow variables around the body. Extension of the method to three dimensions was conceptually straightforward; however, three dimensional applications would also be limited to smooth body geometries although not necessarily to total of nine lines.

Hamilton, H. H., II↗