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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
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 NTRS1978

The response of heat-shield materials to intense laser radiation

Experimental results for the response of ATJ graphite, Carbitex 100, and carbon phenolic to intense continuous-wave laser radiation are presented. Both penetration and mass-loss test techniques are used and compared. The results are also compared with a simple ablation theory applicable to laser irradiation. Reasons for the disparity between experiment and theory, and applicability of the results to other heating situations, such as planetary entry, are discussed.

Lundell, J. H.↗
NASA NTRS1978

Carbonaceous materials subjected to extreme heating - A comparison of numerical simulation and experiments

The ablation of carbonaceous materials in a hydrogen-helium stream has been simulated using a charring materials ablator computer code. These results are compared with the first ablation data to be obtained from the Ames-NASA Giant Planet Pilot Facility. Test stream diagnostics and ablation effects on convective and radiative heat transfer are discussed since these parameters constitute important input data to the numerical simulation. Graphite ablation was predicted to within 10 to 20%, and carbon-phenolic somewhat less accurately.

Davy, W. C.↗
NASA NTRS1978

The impact of turbulence on a radiating shock layer with coupled ablation injection

This paper provides a description of the potential impact of turbulence on a radiating flow field with large surface blowing. This is accomplished by calculating the forebody flow field with coupled carbon-phenolic mass injection for a probe entering the Jupiter atmosphere. Both laminar and turbulent flow conditions are assumed. For the no blowing solutions, turbulence is shown to have no impact on the surface radiative heating. However, with ablation injection, turbulence significantly increases the surface radiative heating rate. This occurs because the turbulence brings the high temperature gases closer to the surface, thus thinning the cool molecular gases at the wall which are responsible for blocking much of the radiation.

Moss, J. N.↗
NASA NTRS1979

Radiation absorption by the C2 band systems for Jupiter entry conditions

Revised values of the absorption cross sections for seven electronic band systems of C2 have been calculated using recently published experimental data for the electronic transition moments. Using these revised C2 cross section values, computations were made for the radiating flow field over a Jupiter entry probe with coupled ablation injection from a carbon-phenolic heat shield. Results are presented which show that radiation absorption within the ablation layer for the spectral range of 4 to 6 eV is less than that predicted using previous C2 absorption cross section values. The effect of the reduced radiation absorption by the C2 molecule is an increase in the radiative heating rates and ablation mass loss rates for the Jupiter entry conditions considered in the study.

Sutton, K.↗
NASA NTRS1979

Numerical simulation of experiments in the Giant Planet Facility

Utilizing a series of existing computer codes, ablation experiments in the Giant Planet Facility are numerically simulated. Of primary importance is the simulation of the low Mach number shock layer that envelops the test model. The RASLE shock-layer code, used in the Jupiter entry probe heat-shield design, is adapted to the experimental conditions. RASLE predictions for radiative and convective heat fluxes are in good agreement with calorimeter measurements. In simulating carbonaceous ablation experiments, the RASLE code is coupled directly with the CMA material response code. For the graphite models, predicted and measured recessions agree very well. Predicted recession for the carbon phenolic models is 50% higher than that measured. This is the first time codes used for the Jupiter probe design have been compared with experiments.

Green, M. J.↗
NASA NTRS1980

Some experience with arc-heater simulation of outer planet entry radiation

An electric arc heater was operated at 800 amperes and 100,000 pa (1 atm) with hydrogen, helium, and two mixtures of hydrogen and helium. A VUV-scanning monochromator was used to record the spectra from an end view while a second spectrometer was used to determine the plasma temperature using hydrogen continuum radiation at 562 nm. Except for pure helium, the plasma temperature was found to be too low to produce significant helium radiation, and the measured spectra were primarily the hydrogen spectra with the highest intensity in the pure hydrogen case. A radiation computer code was used to compute the spectra for comparison to the measurements and to extend the study to simulation of outer planet entry radiation. Conductive cooling prevented ablation of phenolic carbon material samples mounted inside the arc heater during a cursory attempt to produce radiation absorption by ablation gases.

Wells, W. L.↗
NASA NTRS1980

Laminar and turbulent flow solutions with radiation and ablation injection for Jovian entry

Laminar and turbulent flow-field solutions with coupled carbon-phenolic mass injection are presented for the forebody of a probe entering a nominal Jupiter atmosphere. Solutions are obtained for a 35-degree hyperboloid and for a 45-degree spherically blunted cone using a time-dependent, finite-difference method. The radiative heating rates for the coupled laminar flow are significantly reduced as compared to the corresponding no-blowing case; however, for the coupled turbulent flow, it is found that the surface radiative heating rates are substantially increased and often exceed the corresponding no-blowing values. Turbulence is found to have no effect on the surface radiative heating rates for the no-blowing solutions. The present results are compared with the other available solutions, and some additional solutions are presented.

Kumar, A.↗
NASA NTRS1980

Shape change of Galileo probe models in free-flight tests

Scale models of the Galileo Probe made of polycarbonate, AXF5Q graphite, carbon-carbon composite, and carbon-phenolic were flown in a free flight range in an ambient gas of air, krypton, or xenon. Mach numbers varied between 14 and 24, Reynolds numbers between 300,000 and 1,000,000, stagnation pressures between 31 and 200 atm, and stagnation point heat transfer rates between 10 and 1,000 kW/sq cm. Shadowgraphs indicate gouging ablation of the aft portion of the frustum; the gouging was moderate in air and severe in the noble gases. The graphite models break in the same region. An explanation of the phenomena is offered in terms of the strong compression and shear caused by the reattachment of a turbulent separated flow. Conditions are calculated for similar tests appropriate for Von Karman Facility of the Arnold Engineering Development Center in which a larger model can be flown in argon.

Park, C.↗
NASA NTRS1980

Laminar and turbulent flow solutions with radiation and ablation injection for Jovian entry

Laminar and turbulent flowfield solutions with coupled carbon-phenolic mass injection are presented for the forebody of a probe entering a nominal Jupiter atmosphere. Solutions are obtained for a 35-deg hyperboloid and for a 45-deg spherically blunted cone using a time-dependent finite-difference method. The radiative heating rates for the coupled laminar flow are significantly reduced as compared to the corresponding no-blowing case; however, for the coupled turbulent flow, it is found that the surface radiative heating rates are substantially increased and often exceed the corresponding no-blowing values. Turbulence is found to have no effect on the surface radiative heating rates for the no-blowing solutions. The present results are compared with the other available solutions and some additional solutions are presented.

Kumar, A.↗
NASA NTRS1980

Preliminary thermal analysis for Saturn entry

A preliminary thermal analysis based on recently defined Saturn entry conditions has been conducted. The study, using viscous-shock-layer and engineering codes employed for Project Galileo, investigated nonequilibrium chemistry effects on the Saturn thermal environment, defined the primary heat-transfer mode for heatshield design, delineated some problem areas for future thermal studies, and validated BIRCHES (Blunt Body Inviscid Radiative and Convective Heating Engineering Solutions) for parametric or design studies. The effect of nonequilibrium chemistry appears to significantly influence only the radiative fluxes with effects localized to the stagnation region. However, the heat-transfer mode pertinent to the overall heat-shield design is convection. The convective results of BIRCHES and a detailed code are in good agreement. The resulting mass-loss rates for the currently prescribed nominal Saturn entry conditions are small when compared with the values for nominal Jupiter entry conditions. With coupled carbon-phenolic ablation injection, the convective heating rates are reduced substantially while the radiative heating rates are increased when compared with the corresponding no-injection results.

Zoby, E. V.↗
NASA NTRS1980

Influence of nonequilibrium radiation and shape change on aerothermal environment of Jovian entry body

Radiative transfer equations are derived under nonequilibrium conditions which include multilevel energy transitions. The nonequalibrium results, obtained with and without ablation injection in the shock layer, are found to be greatly influenced by the temperature distribution in the shock layer. In the absence of ablative products, the convective and radiative heating to the entry body are reduced significantly under nonequilibrium conditions. The influence of nonequilibrium is found to be greater at higher entry altitudes. With coupled ablation and carbon phenolic injection, 16 chemical species are used in the ablation layer for radiation absorption. Equilibrium and nonequilibrium results are compared under peak heating conditions. A 45 degree sphere cone, a 35 degree hyperboloid, and a 45 degree ellipsoid were used to study probe shape change. Results indicate that the shock layer flow field and heat transfer to the body are influenced significantly by the probe shape change. The effect of shape change on radiative heating of the afterbodies is found to be considerably larger for the sphere cone and ellipsoid than for the hyperboloid.

Tiwari, S. N.↗
NASA NTRS1981

Development of a window protection assembly for a shuttle experiment

A window environmental protection assembly developed for the shuttle infrared leeside temperature experiment is described. The assembly consists of a carbon phenolic composite window mount which contains two silicon windows, a fibrous environmental protection plug to protect the windows during launch operations and ascent heating, a release mechanism used to jettison the plug just prior to atmospheric entry, and two pin puller mechanisms which retain the plug. The plug is released from the window mount assemblies using pneumatic pin pullers and separation springs in the release mechanism. The assembly was designed and tested to withstand the severe mechanical and thermal environments which could be experienced at the top of the shuttle orbiter vertical stabilizer during the ascent, on-orbit, and entry periods of the shuttle trajectory.

Bradley, O. H., Jr.↗
NASA NTRS1981

Influence of nonequilibrium radiation and shape change on aerothermal environment of a Jovian entry body

The influence of nonequilibrium radiative energy transfer and the effect of probe configuration changes on the flow phenomena around a Jovian entry body are investigated. The radiating shock layer flow is assumed to be axisymmetric, viscous, laminar and in chemical equilibrium. The radiative transfer equations are derived under nonequilibrium conditions which include multilevel energy transitions. The equilibrium radiative transfer analysis is performed with an existing nongray radiation model which accounts for molecular band, atomic line, and continuum transitions. The nonequilibrium results are obtained with and without ablation injection in the shock layer. The nonequilibrium results are found to be greatly influenced by the temperature distribution in the shock layer. In the absence of ablative products, the convective and radiative heating to the entry body are reduced under nonequilibrium conditions. The influence of nonequilibrium is found to be greater at higher entry altitudes. With coupled ablation and carbon phenolic injection, 16 chemical species are used in the ablation layer for radiation absorption. Equilibrium and nonequilibrium results are compared under peak heating conditions.

Tiwari, S. N.↗
NASA NTRS1980

Performance of entry heat shields on Pioneer Venus probes

The Pioneer Venus probes approached Venus with high relative velocity. As they entered the atmosphere, they were rapidly decelerated by aerodynamic drag, and a great deal of heat was generated. To protect the probe structure and the scientific instruments, a carbon phenolic heat shield was placed on the front of the probes. Because the design of heat shields for planetary entry is a developing technology, thermocouples were placed in the heat shields so that actual and predicted heat shield performance could be compared. The function of the heat shield is discussed, the probe environments during entry into the Venusian atmosphere are described, and some results from the heat shield experiment are presented. It was found that for the most part, the heat shields performed better than expected.

Pitts, W. C.↗
NASA NTRS1981

Survey of the supporting research and technology for the thermal protection of the Galileo Probe

The Galileo Probe, which is scheduled to be launched in 1985 and to enter the hydrogen-helium atmosphere of Jupiter up to 1,475 days later, presents thermal protection problems that are far more difficult than those experienced in previous planetary entry missions. The high entry speed of the Probe will cause forebody heating rates orders of magnitude greater than those encountered in the Apollo and Pioneer Venus missions, severe afterbody heating from base-flow radiation, and thermochemical ablation rates for carbon phenolic that rival the free-stream mass flux. This paper presents a comprehensive survey of the experimental work and computational research that provide technological support for the Probe's heat-shield design effort. The survey includes atmospheric modeling; both approximate and first-principle computations of flow fields and heat-shield material response; base heating; turbulence modelling; new computational techniques; experimental heating and materials studies; code validation efforts; and a set of 'consensus' first-principle flow-field solutions through the entry maneuver, with predictions of the corresponding thermal protection requirements.

Howe, J. T.↗
NASA NTRS1980

User's guide for the computer code COLTS for calculating the coupled laminar and turbulent flow over a Jovian entry probe

A user's guide for a computer code 'COLTS' (Coupled Laminar and Turbulent Solutions) is provided which calculates the laminar and turbulent hypersonic flows with radiation and coupled ablation injection past a Jovian entry probe. Time-dependent viscous-shock-layer equations are used to describe the flow field. These equations are solved by an explicit, two-step, time-asymptotic finite-difference method. Eddy viscosity in the turbulent flow is approximated by a two-layer model. In all, 19 chemical species are used to describe the injection of carbon-phenolic ablator in the hydrogen-helium gas mixture. The equilibrium composition of the mixture is determined by a free-energy minimization technique. A detailed frequency dependence of the absorption coefficient for various species is considered to obtain the radiative flux. The code is written for a CDC-CYBER-203 computer and is capable of providing solutions for ablated probe shapes also.

Kumar, A.↗
NASA NTRS1982

Spallation of the Galileo probe heat shield

The Galileo probe heat shield will encounter severe radiative and convective heating during entry into Jupiter's atmosphere. The shield is made of two different carbon phenolic composites; one is chopped-molded, and the other is tape-wrapped, both of which tend to spall under intense heating conditions. To characterize this phenomenon, an experimental program, using a gasdynamic laser, was initiated. Tests were performed at a variety of radiation intensities, and both the total and spallation mass-loss rates were measured and correlated with intensity. These correlations were then applied to calculated flight heating conditions for two model atmospheres. Entry of a 310-kg probe into the nominal atmosphere would result in a spallation mass loss of 6.3 kg, or 7.4% of the expected thermochemical mass loss. Similarly, entry of that probe into the cool-dense atmosphere would result in 11.9 kg of spallation, or about 10% of the expected thermochemical mass loss.

Lundell, J. H.↗