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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Siphon flows in isolated magnetic flux tubes. V - Radiative flows with variable ionization

Steady siphon flows in arched isolated magnetic flux tubes in the solar atmosphere are calculated here including radiative transfer between the flux tube and its surrounding and variable ionization of the flowing gas. It is shown that the behavior of a siphon flow is strongly determined by the degree of radiative coupling between the flux tube and its surroundings in the superadiabatic layer just below the solar surface. Critical siphon flows with adiabatic tube shocks in the downstream leg are calculated, illustrating the radiative relaxation of the temperature jump downstream of the shock. For flows in arched flux tubes reaching up to the temperature minimum, where the opacity is low, the gas inside the flux tube is much cooler than the surrounding atmosphere at the top of the arch. It is suggested that gas cooled by siphon flows contribute to the cool component of the solar atmosphere at the height of the temperature minimum implied by observations of the infrared CO bands at 4.6 and 2.3 microns.

Montesinos, Benjamin↗
NASA NTRS1984

Convective and radiative heating of a Saturn entry probe

The extent of convective and radiative heating for a Saturn entry probe is investigated in the absence and presence of ablation mass injection. The flow in the shock layer is assumed to be axisymmetric, viscous and in local thermodynamic equilibrium. The importance of chemical nonequilibrium effects for both the radiative and convective nonblowing surface heating rates is demonstrated for prescribed entry conditions. Results indicate that the nonequilibrium chemistry can significantly influence the rate of radiative heating to the entry probes. With coupled carbon-phenolic ablation injection, the convective heating rates are reduced substantially. Turbulence has little effect on radiative heating but it increases the convective heating considerably.

Tiwari, S. N.↗
NASA NTRS1989

Aerothermodynamics of manned Mars missions

The aerothermodynamic problems associated with the aerobraking of the spacecraft proposed for the manned Mars mission are studied. The propulsive Delta V necessary at departure from earth and Mars and the velocities of the atmospheric entries into the two planets are deduced. It is shown that the propulsive Delta V can be reduced by increasing the entry velocities and that entry velocities up to about 15 km/sec are appropriate at both earth and Mars. L/D values of 0.8 and 2.0 are found to be necessary at earth and Mars, respectively. Density, pressure, and stagnation-point convective-heat-transfer rates are calculated for the typical aerobraking flights. Assuming the shock layer flow to be in equilibrium, the stagnation-point radiative-heat-transfer rates are calculated to be larger than the convective-heat-transfer rates. The possible impact of ablation, turbulence, and nonequilibrium are discussed.

Park, Chul↗
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 NTRS2019

Full Facility Shock Frame Simulations of the Electric Arc Shock Tube

Radiative heating computations are performed for high speed lunar return experiments conducted in the Electric Arc Shock Tube (EAST) facility at NASA Ames Research Center. The nonequilibrium radiative transport equations are solved via NASA's in-house radiation code NEQAIR using flow field input from US3D flow solver. The post-shock flow properties for the 10 km/s Earth entry conditions are computed using the stagnation line of a blunt-body and a full facility CFD (Computational Fluid Dynamics) simulation of the EAST shock tube. The shocked gas in the blunt-body flow achieves a thermochemical equilibrium away from the shock front whereas EAST flow exhibits a nonequilibrium behavior due to strong viscous dissipation of the shock by boundary layer. The full-tube flow calculations capture the influence of the boundary layer on the shocked gas state and provide a realistic fluid dynamic input for the radiative predictions. The integrated radiance behind the shock is calculated in NEQAIR for wavelength regimes from Vacuum-UltraViolet (VUV) to InfraRed (IR), which are pertinent to the emission characteristics of high enthalpy shock waves in air. These radiance profiles are validated against corresponding EAST shots. The full-tube simulations successfully predict a sharp radiance peak at the shock front which gets smeared in the test data due to the spatial resolution in the measurements. The full facility based radiance behind the shock shows a slightly better match with the test data in the VUV and Red spectral regions, as compared to that from a blunt-body based predictions. The UV radiance is very similar for both geometries and under-predicts the test behavior. The IR test data matches better with the blunt-body based predictions where the full-tube simulations show a significant over-prediction.

Radiation↗
NASA NTRS1993

Review of chemical-kinetic problems of future NASA missions. I - Earth entries

A number of chemical-kinetic problems related to phenomena occurring behind a shock wave surrounding an object flying in the earth atmosphere are discussed, including the nonequilibrium thermochemical relaxation phenomena occurring behind a shock wave surrounding the flying object, problems related to aerobraking maneuver, the radiation phenomena for shock velocities of up to 12 km/sec, and the determination of rate coefficients for ionization reactions and associated electron-impact ionization reactions. Results of experiments are presented in form of graphs and tables, giving data on the reaction rate coefficients for air, the ionization distances, thermodynamic properties behind a shock wave, radiative heat flux calculations, Damkoehler numbers for the ablation-product layer, together with conclusions.

Park, Chul↗
NASA NTRS1992

X-ray emission from SN 1986J in NGC 891

Using the Position Sensitive Proportional Counter on ROSAT, we detected soft X-ray emission from SN 1986J in NGC 891 approximately nine years after the supernova event. The X-ray emission is characterized by L(x) (0.1-2.5 keV) = 1.6-7 x 10 exp 40 ergs/s, T(x) = 1.0-3.9 keV, and an absorbing column of 5-14 x 10 exp 21/sq cm. The X-ray luminosity, temperature, and absorption column are reproduced surprisingly well in a model where a reverse shock propagates into the outer layers of the exploded star. The large absorbing column is probably intrinsic to the supernova and represents the cooled gas created by a radiative reverse shock.

Bregman, Joel N.↗
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 NTRS1972

On the possibility of Earth reentry simulation of shallow angle Jupiter entry

Possible Earth reentry simulation of shallow-angle (3 to 30 deg) Jupiter entry was investigated in terms of four parameters of the bow shock layer ahead of a blunt vehicle: peak (equilibrium) temperature, peak pressure, peak inward radiative flux, and time-integrated radiative flux. It is shown that simulation ranging from fair to good can be achieved. Reentry is easiest (lowest Earth reentry speed) at steep Earth reentry, in the Earth entry speed range of 15 to 22 km/sec, for both the Jupiter nominal and cool atmospheres. Increased Earth speed is required, generally, for increasing Jupiter entry angle, and for increasing temperature, radiative flux, time-integrated flux and pressure, in that order.

Mcronald, A. D.↗
NASA NTRS1976

Non-thermal processes in large solar flares

The paper examines the significance of particle acceleration processes in large solar flares, and the importance of accelerated particles in the generation of other flare phenomena. Comprehensive observations of the August 1972 series of large flares were used to obtain quantitative estimates of the energetic particle populations, the electromagnetic emissions, and the mass ejections. The fluxes of energetic electrons and protons were derived from observed X-ray and gamma-ray emissions, respectively. The energy input into the solar atmosphere from the collisional losses of these energetic particles is computed as a function of overlying column density, under the assumption that particles are accelerated at a point high in the solar atmosphere and then precipitate down to denser layers. The flash phase radiation, soft X-ray flare plasma, and the interplanetary shock wave can be consistently and quantitatively explained as a result of the interaction of nonrelativistic electrons with the solar atmosphere.

Lin, R. P.↗
NASA NTRS1973

Correlation of heat transfer for the zero pressure gradient hypersonic laminar boundary layer for several gases

A theoretical study of heat transfer for zero pressure gradient hypersonic laminar boundary layers for various gases with particular application to the flows produced in an expansion tube facility was conducted. A correlation based on results obtained from solutions to the governing equations for five gases was formulated. Particular attention was directed toward the laminar boundary layer shock tube splitter plates in carbon dioxide flows generated by high speed shock waves. Computer analysis of the splitter plate boundary layer flow provided information that is useful in interpreting experimental data obtained in shock tube gas radiation studies.

Cook, W. J.↗
NASA NTRS1981

Significance of turbulence and transition location on radiative heating with ablation injection

This paper presents forebody flowfield solutions for Jupiter entry conditions where the ablation injection rate is coupled with the surface heating rate. The calculations are made with a time-dependent viscous-shock-layer analysis where the flow is assumed to be in chemical equilibrium. Both laminar and turbulent solutions are presented to describe the impact of turbulence on surface mass loss rates for flow conditions where the heating is due primarily to radiation. Results are also presented where the transition location to turbulent flow is arbitrarily varied. Results show that the radiative heating rate values based on several downstream transition locations adjust quickly to the corresponding values based on transition near the stagnation point.

Moss, J. N.↗
NASA NTRS1975

A similarity solution of the Navier-Stokes equations with wall catalysis and slip for hypersonic, low Reynolds number flow over spheres

The slip conditions for a multicomponent mixture with diffusion, wall-catalyzed atom recombination and thermal radiation are derived. The more realistic multicomponent species slip conditions are shown to be necessary for accurate merged shock layer solutions on a sphere. These slip conditions are used in a first-order similarity solution of the Navier-Stokes equations with nonequilibrium chemistry for the merged shock layer. Results of this quick numerical solution are compared with a time dependent solution around the sphere and with measured arc jet results at low Reynolds numbers. The similarity solution, unlike the time dependent solution, shows smooth radial profiles of the pressure and smooth variations of velocity slip, skin friction, temperature slip and heat transfer around the body. The present first-order similarity solution is valid up to 25 deg from the stagnation point and takes less than 1% of the computer time to run a time dependent scheme. The smaller stand-off distance obtained from the similarity solution is supported by experimental data. The measured heat flux is closer to the similarity solution than the time dependent method at the stagnation point and shows the proper variation with circumferential angle up to at least 40 deg.

Hendricks, W. L.↗
NASA NTRS2013

Composite Aerogel Multifoil Protective Shielding

New technologies are needed to survive the temperatures, radiation, and hypervelocity particles that exploration spacecraft encounter. Multilayer insulations (MLIs) have been used on many spacecraft as thermal insulation. Other materials and composites have been used as micrometeorite shielding or radiation shielding. However, no material composite has been developed and employed as a combined thermal insulation, micrometeorite, and radiation shielding. By replacing the scrims that have been used to separate the foil layers in MLIs with various aerogels, and by using a variety of different metal foils, the overall protective performance of MLIs can be greatly expanded to act as thermal insulation, radiation shielding, and hypervelocity particle shielding. Aerogels are highly porous, low-density solids that are produced by the gelation of metal alkoxides and supercritical drying. Aerogels have been flown in NASA missions as a hypervelocity particle capture medium (Stardust) and as thermal insulation (2003 MER). Composite aerogel multifoil protective shielding would be used to provide thermal insulation, while also shielding spacecraft or components from radiation and hypervelocity particle impacts. Multiple layers of foil separated by aerogel would act as a thermal barrier by preventing the transport of heat energy through the composite. The silica aerogel would act as a convective and conductive thermal barrier, while the titania powder and metal foils would absorb and reflect the radiative heat. It would also capture small hypervelocity particles, such as micrometeorites, since it would be a stuffed, multi-shock Whipple shield. The metal foil layers would slow and break up the impacting particles, while the aerogel layers would convert the kinetic energy of the particles to thermal and mechanical energy and stop the particles.

Jones, Steven M.↗
NASA NTRS1993

Survey of nonequilibrium re-entry heating for entry flight conditions

A viscous shock layer method has been developed which includes the effects of chemical and thermal nonequilibrium and is coupled with a radiation analysis which includes thermodynamic nonequilibrium effects. This code has been used to obtain solutions for a wide variety of nonequilibrium re-entry conditions in air. The results are tabulated and displayed graphically. Comparisons are made to similar results obtained for radiatively coupled equilibrium flow and conclusions drawn on the effect of nonequilibrium and in particular thermodynamic nonequilibrium on the radiative environment about re-entry vehicles.

Gally, Thomas A.↗
NASA NTRS1960

Motion and Heating During Atmosphere Reentry of Space Vehicles

The results of an analysis of the motion and heating during atmospheric reentry of manned space vehicles has shown the following: 1. Flight-corridor depths which allow reentry in a single pass decrease rapidly as the reentry speed increases if the maximum deceleration is limited to 10 g. 2. Use of aerodynamic lift can result in a three-to five fold increase in corridor depth over that available to a ballistic vehicle for the same deceleration limits. 3. Use of aerodynamic lift to widen these reentry corridors causes a heating penalty which becomes severe for values of the lift-drag ratio greater than unity for constant lift-drag entry. 4. In the region of most intense convective heating the inviscid flow is generally in chemical equilibrium but the boundary-layer flows are out of equilibrium. Heating rates for the nonequilibrium boundary layer are generally lower than for the corresponding equilibrium case. 5. Radiative heating from the hot gas trapped between the shock wave and the body stagnation region may be as severe as the convective heating and unfortunately occurs at approximately the same time in the flight.

Wong, Thomas J.↗
NASA NTRS1978

Radiative shock dynamics. II - Hydrogen continua

The interaction between radiation and a shock wave propagating through a stellar atmosphere is investigated. Departures from local thermodynamic equilibrium (LTE) are permitted in the first two levels of a 10-level hydrogen atom; levels 3-10 are in LTE. A piston moving at constant velocity into the bottom of the atmosphere drives a shock wave. This shock produces precursor radiation that diffuses through the gas well ahead of the shock and causes a mild luminosity flash in the emergent Balmer and free-free radiation when it reaches the surface. The precursor wave deposits a large amount of radiative energy in the outer layers of the atmosphere, initiating a radiation-induced pressure wave. The process of energy transfer from the radiation field to the compression wave is similar to the Eddington valve mechanism which drives stellar pulsations. Material is accelerated outward by the radiation-induced wave; eventually it free-falls inward, hits the quasistationary atmosphere, and forms an accretion shock. The piston driven shock is weakened by radiative energy losses. When it reaches the surface, the shock is invisible in the continuum radiation.

Klein, R. I.↗