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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 199 records · Page 11
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NASA NTRS1976

Turbulent viscous-shock-layer solutions with strong vorticity interaction

Numerical solutions of the viscous-shock-layer equations governing laminar and turbulent flows of a perfect gas and radiating and nonradiating mixtures of perfect gases in chemical equilibrium are presented for hypersonic flow over spherically blunted cones and hyperboloids. The results are compared with boundary-layer and inviscid flow-field solutions. The agreement with the inviscid flow field data is satisfactory. The agreement with boundary-layer solutions is good except in regions of strong vorticity interaction. In these flow regions, the viscous-shock-layer solutions appear to be more satisfactory than the boundary-layer solutions.

Anderson, E. C.↗
NASA NTRS1976

Aerothermal environment for Jovian entry probes

Results are presented that describe the aerothermal environment encountered by the forebody of probes during Jovian entry. Two probe configurations are considered: a 55 deg half-angle spherically blunted cone and a 50 deg half-angle hyperboloid. The main emphasis is focused on defining the heating environment during entry and on determining the effectiveness of coupled ablation injection in reducing the surface heating rate. This is accomplished by calculating both the convective and radiative heating at several points along the entry trajectory both with and without coupled ablation injection. Results are presented for both laminar and turbulent calculations.

Moss, J. N.↗
NASA NTRS1976

An investigation of the effects of mass loss, shape change and real gas aerodynamics on a Jovian atmospheric reconstruction experiment

A survey of the effects of mass loss, shape change and real-gas aerodynamics on a Jovian atmospheric reconstruction experiment is carried out. Techniques used to reconstruct atmospheric profiles from entry probe measurements are discussed and some of the parameters which affect their accuracy are identified. Trajectory analyses and real-gas, radiatively-coupled flow field analyses (which include the effects of mass loss and shape change) are carried out for several candidate probe configurations. From these analyses, uncertainties in the atmospheric reconstruction procedure are estimated. Finally, the prospects for reducing these uncertainties by optimizing probe configuration and by instrumentation of the probe heat shield to measure actual shape change are considered.

Walberg, G. D.↗
NASA NTRS1977

Internal flow characteristics of a multistage compressor with inlet pressure distortion

The measured distribution of compressor interstage pressures and temperatures resulting from a 180 deg inlet-total-pressure distortion for a J85-13 turbojet engine is reported. Extensive inner stage instrumentation combined with stepwise rotation of the inlet distortion gave data of high circumferential resolution. The steady-state pressures and temperatures along with the amplitude, extent, and location of the distorted areas are given. Data for 80, 90, and 100 percent of rotor design speed are compared with clean (undistorted) inlet flow conditions to show pressure and temperature behavior within the compressor. Both overall and stagewise compressor performances vary only slightly when clean and distorted inlet conditions are compared. Total and static pressure distortions increase in amplitude in the first few stages of the compressor and then attenuate fairly uniformly to zero at the discharge. Total-temperature distortion induced by the pressure distortion reached a maximum amplitude by the first two stages and decayed only a little through the rest of the compressor. Distortion amplitude tended to peak in line with the screen edges, and, except for total and static pressure in the tip zone, there was little swirl in the axial direction.

Debogdan, C. E.↗
NASA NTRS1977

Effect of slotted casing treatment with change in Reynolds number index on performance of a jet engine

A tip-treated J85-13 engine was tested at Reynolds number indices (RNI) of 0.3 and 0.7 with a clean inlet for 80- and 100-percent corrected engine speeds. This engine was equipped with a compressor case which allowed changes to the case wall over the rotor tips of six of its eight stages. For all tests, the principal effects were (1) with tip treatment, a stall pressure ratio loss of 6 percent at 100 percent corrected engine speeds for both the 0.3 and 0.7 RNI, and (2) with and without tip treatment, decreasing the RNI from 0.7 to 0.3 decreased the stall pressure ratio 3.8 percent for 100 percent corrected engine speed and 2.8 percent for 80-percent corrected engine speed.

Moss, J. E., Jr.↗
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 NTRS1976

Numerical solution of the steady-state Navier-Stokes equations for hypersonic flow about blunt axisymmetric bodies

The steady-state Navier-Stokes equations are solved for hypersonic flow about blunt axisymmetric bodies. The equations of motion are solved by successive approximations using an implicit finite-difference scheme. The results are compared with viscous shock-layer theory, experimental data, and time-dependent solutions of the Navier-Stokes equations. It is demonstrated that viscous shock-layer theory is sufficiently accurate for the range of flight conditions normally encountered by entry vehicles.

Anderson, E. C.↗
NASA NTRS1977

The effect of ablation injection on radiative and convective heating

A viscous shock-layer analysis for calculating high energy equilibrium flow fields about blunt axisymmetric bodies is applied to the problem of massive ablation injection with radiation transport. A nongray radiation model is used that accounts for both line and continuum radiation. The solution method is direct and provides both stagnation and downstream solutions. Results for shock heated air show that phenolic-nylon injection is substantially more effective in reducing the wall radiant flux than air injection. Also, for large included body angles, the wall radiative flux and the coupled phenolic-nylon injection rate do not continue to decrease with increasing distance downstream.

Moss, J. N.↗
NASA NTRS1977

Development and evaluation of die materials for use in the growth of silicon ribbons by the inverted ribbon growth process, task 2, LSSA project

Silicon sessile drop experiments were performed on a variety of commercially available refractory carbides, nitrides, oxides, and borides to examine the potential of these materials for applications involving either direct contact with molten silicon or as substrates for CVD coatings in the fabrication of dies and crucibles for containing molten silicon. Simultaneous experiments were also conducted with CVD layers of SiC, Si3N4, and SiOxNy. Silicon nitride layers, deposited with NH3:SiH4 ratios ranging from 100:1 down to 5:1, were examined in sessile drop experiments to determine if the layers are degraded as a result of using lower reagent ratios. Preliminary experiments were undertaken on the stability of CVD Si3N4 near the melting point of silicon. Silicon ribbon segments were grown from vitreous carbon dies which had been coated with CVD Si3N4. Depending upon the purity of the die materials, ribbon resistivity values up to 40 Omega cm were obtained.

Duffy, M. T.↗
NASA NTRS1978

An approximate inviscid radiating flow field analysis for outer planet entry probes

An approximate computational technique has been developed for predicting inviscid, radiating flows about blunt probes entering atmospheres consisting of hydrogen and helium. The technique is rapid and versatile and is well suited for performing parametric trade studies for outer planet entries. Details of the computational technique, the thermodynamic correlations, the 58-step absorption coefficient model and the analytic shock shape equations are discussed. Good comparisons of the radiative heating computed by the approximate method and by detailed calculations are obtained.

Zoby, E. V.↗
NASA NTRS1978

Radiative flux penetration through a blown shock layer for Jupiter entry conditions

A study is made of the radiative blockage due to carbonaceous ablation injection for a probe entering the Jupiter atmosphere. This is accomplished by calculating the stagnation-point blockage factors for three entry trajectories that account for variations in probe configuration, atmospheric gas composition, and entry conditions. The radiative blockage within the relatively cool ablation layer is shown to be large and to be primarily dependent upon the absorption of the C2 and C3 species. The C3 absorption is significant, particularly when the new experimental data for C3 spectral absorption properties are used. Also, the stagnation-point radiative blockage factors are shown to correlate well in terms of the no-injection radiative heating rates for various entry conditions.

Moss, J. N.↗
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 NTRS1978

Development and evaluation of die materials for use in the growth of silicon ribbons by the inverted ribbon growth process, task 2. LSSA project

The results of emission spectroscopic analysis indicate that molten silicon can remain in contact with hot-pressed Si3N4 (99.2 percent theoretical density) for prolonged periods without attaining the impurity content level of the nitride. Although MgO was used as binder, Mg was not found present in the silicon sessile drop in quantities much above the level initially present in the silicon source material. Preliminary experiments with EFG-type dies coated with CVD Si3N4 or CVD SiOxNy indicate that capillary rise does not occur readily in these dies. The same was found to be true of hot-pressed and reaction-sintered Si3N4 obtained commercially. However, when dies were formed by depositing CVD layers on shaped silicon slabs, a column of molten silicon was maintained in each CVD die while being heated in contact with a crucible of molten silicon. Preliminary wetting of dies appears necessary for EFG growth. Several ribbon growth experiments were performed from V-shaped dies.

Duffy, M. T.↗
NASA NTRS1978

Development and Evaluation of Die Materials for Use in the Growth of Silicon Ribbons by the Inverted Ribbon Growth Process. Task 2: LSSA Project

Several ribbon growth experiments were performed from V-shaped dies coated with CVD Si3N4. The most significant result was the ability to perform five consecutive growth runs from the same die without mechanical degradation of the die through temperature cycling. The die was made from vitreous carbon coated with CVD Si3N4. Silicon oxynitride, Si2N2O, was examined with respect to thermal stability in contact with molten silicon. The results of X-ray analysis indicate that this material is converted to both alpha - and beta-Si3N4 in the presence of molten silicon. Experiments on the stability of CVD SiOxNy shoe that this material can be maintained in contact with molten silicon (sessile drop test) for greater than 30 h at 1450 C without total decompositon. These layers are converted mainly to beta-Si3N4.

Duffy, M. T.↗
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

Flow-field analyses for future planetary entry

Scientific exploration of the planets by means of instrumented probes and landers provides a means of enhancing our knowledge concerning the solar system. A prime requirement for a successful planetary entry mission is that the design of a vehicle be based on a reliable definition of the aerothermal environment encountered during entry. This paper briefly reviews some of the past developments and current examples of computational flow-field analyses for predicting the aerothermal environment of planetary probes. All of the flow-field solutions presented are for a very severe aerothermal entry environment, representative of the entry environment that the Galileo probe will encounter when it enters Jupiter's atmosphere in 1985. Finally, areas for analysis improvements and extensions are identified for current and future planetary missions.

Moss, J. N.↗
NASA NTRS1979

Approximate convective heating equations for hypersonic flows

Laminar and turbulent heating-rate equations appropriate for engineering predictions of the convective heating rates about blunt reentry spacecraft at hypersonic conditions are developed. The approximate methods are applicable to both nonreacting and reacting gas mixtures for either constant or variable-entropy edge conditions. A procedure which accounts for variable-entropy effects and is not based on mass balancing is presented. Results of the approximate heating methods are in good agreement with existing experimental results as well as boundary-layer and viscous-shock-layer solutions.

Zoby, E. V.↗