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At least 1,747 records · Page 97
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

An algorithm for selecting a radiation transport subgrid for ablation and radiation coupled hypersonic viscous shock-layer problems

An algorithm is described for selecting a grid subset for calculating radiative transport. The subset spacing is determined by using the variation in aerothermal properties across the full grid of the shock layer. Results show that a radiation grid subset of 15 to 20 points can be used for viscous-shock layer calculations where approximately 50 grid points are required to define the aerothermal profiles. Results are presented for various planetary entry conditions with and without mass injection to demonstrate both the validity and utility of the algorithm.

Bolz, C. W., Jr.↗
NASA NTRS1976

Entry into outer planet environments. I - The radiating shock layer with coupled ablation for carbon and silica

Fully coupled solutions of shock layer equations for the stagnation region are obtained, comprising a set of converged benchmark flowfield solutions for silica and carbon heat shields entering modeled atmospheres of Saturn and Uranus. Model atmospheres and entry trajectories providing significant radiative heating to the entry probes so that the heating environment and effects of mass addition on the heating environment are clearly defined are emphasized. Results referable to the carbon heat shield are questioned because of the high (sublimation) wall temperature assumed and the relatively low shock layer temperature.

Liu, C.-H.↗
NASA NTRS1976

Study of the ablative effects on tektites

Equations are presented which provide approximate parameters describing surface heating and tektite deceleration during atmosphere passage. Numerical estimates of these parameters using typical initial and ambient conditions support the conclusion that the commonly assumed trajectories would not have produced some of the observed surface markings. It is suggested that tektites did not enter the atmosphere singly but rather in a swarm dense enough to afford wake shielding according to a shock envelope model which is proposed. A further aerodynamic mechanism is described which is compatible with hemispherical pits occurring on tektite surfaces.

Sepri, P.↗
NASA NTRS1977

Experimental verification of the technique for measurement of ablation on the GASJET nose tip

The GASJET nose tip is proposed to reduce the erosion at the apex of a missile nose flying at hypersonic speeds through a rain storm as it reenters the atmosphere. A forward facing sonic jet is directed through the tip introducing a secondary counter-flow which displaces the bow shock and blankets the tip with a protective layer of relatively cool gas. Wind tunnel experiments are described which proved the validity of measuring nose recession in flight by recording the pressure in the blast tube supplying the GASJET.

Donohoe, J. C.↗
NASA NTRS1978

Supersonic flow over ablated nosetips using an unsteady, implicit numerical procedure

The axisymmetric supersonic flow over passive, that is, nonablating, indented nosetips of reentry vehicles is determined using an unsteady implicit numerical algorithm which solves either the inviscid Euler equations or the 'thin-layer' Navier-Stokes equations. A nonorthogonal independent variable transformation is used to map the distorted physical region, containing multiple zones of embedded subsonic flow into a rectangular computational domain at whose boundaries the required permeable or impermeable boundary conditions are simulated. Use of the implicit algorithm results in faster convergence to the steady state because of a larger allowable time step over conventional explicit schemes. The numerical results obtained compare favorably with existing experimental data for very mildly and severely indented blunt nosetips.

Kutler, P.↗
NASA NTRS1979

Transient thermal response of ablating bodies

A numerical study of transient thermal response of a blunt-nosed axisymmetric body made of Teflon is presented using a two-layer thermal model. It is shown that phase change and transverse heat conduction have a considerable effect on the internal temperature field. Comparison of the numerical results with experimental data shows that the single-layer thermal model does not predict the real feature of the thermal field, whereas the results of the two-layer thermal model agree reasonably well with the experiment.

Arai, N.↗
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

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

Supersonic flow over three-dimensional ablated nosetips using an unsteady implicit numerical procedure

The three-dimensional supersonic flow over passive, that is, nonablating, indented nosetips of reentry vehicles is determined using an unsteady implicit numerical algorithm which solves either the inviscid Euler equations or the 'thin-layer' Navier-Stokes equations. A nonorthogonal independent variable transformation is used to map the distorted physical domain, containing multiple zones of embedded subsonic flow and separated flow regions into a rectangular computational volume at whose boundaries the required permeable or impermeable boundary conditions are simulated. Use of the implicit algorithm results in faster convergence to the steady state because of a larger allowable time step over conventional explicit schemes. The numerical results obtained compare favorably with existing numerical solutions and experimental data for simple spheres which validates the program. Results are also presented for analytically defined indented bodies for both laminar and turbulent flow conditions that demonstrate the program's capability for computing such flows.

Kutler, P.↗
NASA NTRS1980

Influence of nonequilibrium radiation on heating of an ablating Jovian entry probe

The influence of non-local thermodynamic equilibrium (NLTE) radiative transfer on the entire shock-layer flow phenomena around a Jovian entry body is investigated. The flow in the shock layer is assumed to be viscous, axisymmetric, laminar, and in chemical equilibrium. The entry body considered is a 35-deg hyperboloid and the results have been obtained for the peak heating entry conditions. The results indicate that the radiative heating of the entry body is significantly higher under NLTE conditions.

Tiwari, S. N.↗
NASA NTRS1981

Experimental determination of ablation vapor species from carbon phenolic heat-shield materials

The relative concentrations of vapors produced from carbon phenolic composites under thermal loadings approximating those expected at peak heating during vehicle entry into the atmospheres of the outer planets have been determined. The technique of vaporizing the surface of bulk samples by laser irradiation while measuring in situ the vapor species by mass spectrometry is described. Results show that vapor composition varies with irradiance level and with depth of heating (or extent of pyrolysis). Attempts are made to compare these experimental results with the theoretical predictions from computer codes.

Lincoln, K. A.↗
NASA NTRS1981

The effect of modeled turbulence on a hypersonic shock layer with massive ablation injection

For the first time, candidate turbulence models are analyzed for shock-layer conditions as severe as those of a Jovian entry. The various models investigated are two standard models developed primarily by Cebeci (1970) and Kendall (1972), and two modifications of the standard models developed primarily by Baldwin and Lomax (1978) and by Nicolet (1979). The analysis is conducted within the context of a new, viscous shock-layer flow-field code, to properly isolate differences in performance among the various models. This code retains all terms in the Navier-Stokes equations necessary to describe the unique flow events, and incorporates computational features that greatly facilitate the analysis of such events. The relative superiority of the turbulence models cannot be determined from this study alone; however, insight is provided into the relative severity of the various models. In addition, attention is focused on an important research area for experimental and theoretical investigation to develop realistic turbulence models.

Menees, G. P.↗
NASA NTRS1982

Development of toughened epoxy polymers for high performance composite and ablative applications

A survey of current procedures for the assessment of state of cure in epoxy polymers and for the evaluation of polymer toughness as related to nature of the crosslinking agent was made to facilitate a cause-effect study of the chemical modification of epoxy polymers. Various conformations of sample morphology were examined to identify testing variables and to establish optimum conditions for the selected physical test methods. Dynamic viscoelasticity testing was examined in conjunction with chemical analyses to allow observation of the extent of the curing reaction with size of the crosslinking agent the primary variable. Specifically the aims of the project were twofold: (1) to consider the experimental variables associated with development of "extent of cure" analysis, and (2) to assess methodology of fracture energy determination and to prescribe a meaningful and reproducible procedure. The following is separated into two categories for ease of presentation.

Allen, V. R.↗
NASA NTRS1985

Charge-to-mass dispersion methods for abrasion-ablation fragmentation models

Methods to describe the charge-to-mass dispersion distributions of projectile prefragments are presented and used to determine individual isotope cross-sections or various elements produced in the fragmentation of relativistic argon nuclei by carbon targets. Although slight improvements in predicted cross-sections are obtained for the quantum mechanical giant dipole resonance (GDR) distribution when compared qith the predictions of the geometric GDR model, the closest agreement between theory and experiment continues to be obtained with the simple hypergeometric distribution, which treats the nucleons in the nucleus as completely uncorrelated.

Townsend, L. W.↗