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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 1,567 records · Page 87
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Two-dimensional simulation of a two-phase, regenerative pumped radiator loop utilizing direct contact heat transfer with phase change

An innovative pumped loop concept for 600 K space power system radiators utilizing direct contact heat transfer, which facilitates repeated startup/shutdown of the power system without complex and time-consuming coolant thawing during power startup, is under development. The heat transfer process with melting/freezing of Li in an NaK flow was studied through two-dimensional time-dependent numerical simulations to characterize and predict the Li/NaK radiator performance during startup (thawing) and shutdown (cold-trapping). Effects of system parameters and the criteria for the plugging domain are presented together with temperature distribution patterns in solid Li and subsequent melting surface profile variations in time.

Rhee, Hyop S.↗
NASA NTRS1991

Stability of compressible Taylor-Couette flow

Compressible stability equations are solved using the spectral collocation method in an attempt to study the effects of temperature difference and compressibility on the stability of Taylor-Couette flow. It is found that the Chebyshev collocation spectral method yields highly accurate results using fewer grid points for solving stability problems. Comparisons are made between the result obtained by assuming small Mach number with a uniform temperature distribution and that based on fully incompressible analysis.

Kao, Kai-Hsiung↗
NASA NTRS1991

Mixing of multiple jets with a confined subsonic crossflow - Summary of NASA-supported experiments and modeling

Experimental and computational results on the mixing of single, double, and opposed rows of jets with an isothermal or variable temperature mainstream in a confined subsonic crossflow are summarized. The studies were performed to investigate flow and geometric variations typical of the complex 3D flowfield in the dilution zone of combustion chambers in gas turbine engines. The principal observations from the experiments were that the momentum-flux ratio was the most significant flow variable, and that temperature distributions were similar (independent of orifice diameter) when the orifice spacing and the square-root of the momentum-flux ratio were inversely proportional. The experiments and empirical model for the mixing of a single row of jets from round holes were extended to include several variations typical of gas turbine combustors.

Holdeman, James D.↗
NASA NTRS1991

Efficient numerical method for computation of the thermohydrodynamics of laminar lubricating films

The purpose of this paper is to describe an accurate, yet economical, method for computing temperature effects in laminar lubricating films in two dimensions. Because of the marked dependence of lubricant viscosity on temperature, the effect of viscosity variation both across and along a lubricating film can dwarf other deviations from ideal constant-property lubrication. In practice, a thermohydrodynamics program will involve simultaneous solution of the film lubrication problem, together with heat conduction in a solid, complex structure. In pursuit of computational economy, techniques similar to those for Gaussian quadrature are used; it is shown that, for many purposes, the use of just two properly positioned temperatures (Lobatto points) characterizes the transverse temperature distribution.

Elrod, H. G.↗
NASA NTRS1991

Flow visualization and computational studies of a reverse flow circular combustor

The development of a reverse-flow circular combustor is described in terms of the visualization techniques that are employed to optimize the flow and mixing of fuel and air. The Fluent computer program is used in conjunction with flow visualization studies to investigate the performance of the combustor. The combustor has multiple mini-combustion zones (MCZs) and fuel injection nozzles along its circular geometry, and the fuel injection design is modeled to determine temperature distribution, including the performance at the combustor exit. The yellow dye smoke used in the visualization demonstrated desirable flow patterns with rapid circulation patterns within the MCZs and extensive interaction between the channel flow and the MCZs. The results are similar to those of CFD models, and the main conclusions are that fuel atomization can be further optimized and that the fuel injector nozzle can control swirls, fuel spray angle, and jet penetration.

Ghorashi, B.↗
NASA NTRS1991

Contributions to the implementation of the Arakawa-Schubert cumulus parameterization in the GLA GCM

The roles of the Critical Cloud Work Function (CCWF) data set and the upper and lower bounds on entrainment by cumulus plumes in the Arakawa-Schubert cumulus parameterization (ASCP) in the GLA GCM (Geller et al., 1988) were investigated in two sets of experiments. It was found that the horizontal and vertical distribution of cumulus heating can be altered in ASCP by adjusting these parameters. These changes can have a strong influence on the vertical structure of condensation heating, water vapor distribution, temperature, and rainfall. The CCWF is an important limiting parameter that controls the onset of different cloud types; increasing the threshold values of CCWF for all clouds tends to concentrate the rainfall into a narrower ITCZ and affects the rainfall during the initial adjustment period.

Sud, Y. C.↗
NASA NTRS1991

X-ray irradiation of interstellar grains in active galaxies - Evaporation and infrared spectra

A fundamental physical study of grains heated transiently by X-rays is presented. The X-ray photoionization cross sections used to determine the rate of energy deposition into the grains are given. A grain model is constructed and the radiative and evaporative responses of grains into X-ray absorption are described. The basic theory of stochastic grain heating is outlined, and analytical expressions for the temperature distributions of flickering grains are provided. The resulting IR spectra due to X-ray illumination are given, and the relevance of the present work to the IR continua of active galaxies is discussed. The present model provides two observational predictions: the infrared spectra of grains, even if they are superheated, should show a cutoff between 1 and 3 microns; and X-ray-illuminated environments should exhibit no PAH emissions.

Voit, G. M.↗
NASA NTRS1991

Analysis of flight-measured boundary-layer stability and transition data

The paper concentrates on the computational analysis of both the Tollmien-Schlichting and crossflow-type instabilities using the results of a boundary-layer transition flight experiment on a smooth swept test surface. In addition, the effect of nonadiabatic wall conditions is analyzed using the measured surface temperature distribution on the boundary-layer development and stability growth. The computational methods utilized in analyzing the boundary-layer stability characteristics are discussed: one approach analyzes the Tollmien-Schlichting and crossflow instabilities independently with maximum Tollmien-Schlichting n-factors near nine and maximum crossflow n-factors near six at transition onset for separate cases, while the second approach analyzes the instabilities for maximum growth regardless of the type. As much as a 27-percent increase in n-factor is found at transition onset due to an increased Tollmien-Schlichting instability.

Obara, Clifford J.↗
NASA NTRS1992

Determining Asymmetry Of A Weld Puddle

Sensing-and-data-processing subsystem provides information of asymmetry of weld puddle with respect to original midplane of joint. Shape of puddle inferred from surface-temperature distribution. Part of welding-control system which enables system to correct for asymmetry.

Gutow, David A.↗
NASA NTRS1991

Thermal modeling of comet Kopff: Implications for the CRAF mission

A thermal model of periodic comet Kopff was developed to aid in planning for the Comet Rendezvous Asteroid Flyby mission. The model is based on the comet nucleus model, which estimates the surface temperature distribution and sublimation rates on a rotating icy sphere in heliocentric orbit. The model results are compared with the observed gas production rates from Kopff in 1983. It is found that approximately 15 percent of the sunlit nucleus surface is active, a relatively high fraction for a typical short-period comet. This suggests that the actual nucleus radius may be larger than the model value. The slope of the observed gas production curve with heliocentric distance is steeper than that predicted by the thermal model. This may indicate the existence of a more complex process than direct sublimation of surface ices, such as gas diffusion through a nonvolatile insulating crust.

Weissman, Paul↗
NASA NTRS1991

Wire core reactor for NTP

The development of the wire core system for Nuclear Thermal Propulsion (NTP) that took place from 1963 to 1965 is discussed. A wire core consists of a fuel wire with spacer wires. It's an annular flow core having a central control rod. There are actually four of these, with beryllium solid reflectors on both ends and all the way around. Much of the information on the concept is given in viewgraph form. Viewgraphs are presented on design details of the wire core, the engine design, engine weight vs. thrust, a technique used to fabricate the wire fuel element, and axial temperature distribution.

Harty, R. B.↗
NASA NTRS1991

Spectral fitting, shock layer modeling, and production of nitrogen oxides and excited nitrogen

An analysis was made of N2 emission from 8.72 MJ/kg shock layer at 2.54, 1.91, and 1.27 cm positions and vibrational state distributions, temperatures, and relative electronic state populations was obtained from data sets. Other recorded arc jet N2 and air spectral data were reviewed and NO emission characteristics were studied. A review of operational procedures of the DSMC code was made. Information on other appropriate codes and modifications, including ionization, were made as well as a determination of the applicability of codes reviewed to task requirement. A review was also made of computational procedures used in CFD codes of Li and other codes on JSC computers. An analysis was made of problems associated with integration of specific chemical kinetics applicable to task into CFD codes.

Blackwell, H. E.↗
NASA NTRS1990

Climatological stratospheric modeling

The Goddard Institute for Space Studies (GISS) Three dimensional Global Climate/Middle Atmosphere Model was used to investigate the effect of doubled carbon dioxide on the middle atmosphere. Carbon dioxide was doubled in both the troposphere and stratosphere, and the sea surface temperatures were increased in accordance with results from the GISS climate model. Additional experiments were run with different sea surface temperature distributions, and doubling the carbon dioxide only in the troposphere or stratosphere.

Rind, David↗
NASA NTRS1992

Orbital transfer rocket engine technology program: Soft wear ring seal technology

Liquid oxygen (LOX) compatibility tests, including autogenous ignition, promoted ignition, LOX impact tests, and friction and wear tests on different PV products were conducted for several polymer materials as verification for the implementation of soft wear ring seals in advanced rocket engine turbopumps. Thermoplastics, polyimide based materials, and polyimide-imide base materials were compared for oxygen compatibility, specific wear coefficient, wear debris production, and heat dissipation mechanisms. A thermal model was generated that simulated the frictional heating input and calculated the surface temperature and temperature distribution within the seal. The predictions were compared against measured values. Heat loads in the model were varied to better match the test data and determine the difference between the measured and the calculated coefficients of friction.

Lariviere, Brian W.↗
NASA NTRS1992

Full Navier-Stokes analysis of a two-dimensional mixer/ejector nozzle for noise suppression

A three-dimensional full Navier-Stokes (FNS) analysis was performed on a mixer/ejector nozzle designed to reduce the jet noise created at takeoff by a future supersonic transport. The PARC3D computational fluid dynamics (CFD) code was used to study the flow field of the nozzle. The grid that was used in the analysis consisted of approximately 900,000 node points contained in eight grid blocks. Two nozzle configurations were studied: a constant area mixing section and a diverging mixing section. Data are presented for predictions of pressure, velocity, and total temperature distributions and for evaluations of internal performance and mixing effectiveness. The analysis provided good insight into the behavior of the flow.

Debonis, James R.↗
NASA NTRS1992

Dynamic interactions between hypersonic vehicle aerodynamics and propulsion system performance

Described here is the development of a flexible simulation model for scramjet hypersonic propulsion systems. The primary goal is determination of sensitivity of the thrust vector and other system parameters to angle of attack changes of the vehicle. Such information is crucial in design and analysis of control system performance for hypersonic vehicles. The code is also intended to be a key element in carrying out dynamic interaction studies involving the influence of vehicle vibrations on propulsion system/control system coupling and flight stability. Simple models are employed to represent the various processes comprising the propulsion system. A method of characteristics (MOC) approach is used to solve the forebody and external nozzle flow fields. This results in a very fast computational algorithm capable of carrying out the vast number of simulation computations needed in guidance, stability, and control studies. The three-dimensional fore- and aft body (nozzle) geometry is characterized by the centerline profiles as represented by a series of coordinate points and body cross-section curvature. The engine module geometry is represented by an adjustable vertical grid to accommodate variations of the field parameters throughout the inlet and combustor. The scramjet inlet is modeled as a two-dimensional supersonic flow containing adjustable sidewall wedges and multiple fuel injection struts. The inlet geometry including the sidewall wedge angles, the number of injection struts, their sweepback relative to the vehicle reference line, and strut cross-section are user selectable. Combustion is currently represented by a Rayleigh line calculation including corrections for variable gas properties; improved models are being developed for this important element of the propulsion flow field. The program generates (1) variation of thrust magnitude and direction with angle of attack, (2) pitching moment and line of action of the thrust vector, (3) pressure and temperature distributions throughout the system, and (4) performance parameters such as thrust coefficient, specific impulse, mass flow rates, and equivalence ratio. Preliminary results are in good agreement with available performance data for systems resembling the NASP vehicle configuration.

Flandro, G. A.↗
NASA NTRS1992

On the physics of waves in the solar atmosphere: Wave heating and wind acceleration

In the area of solar physics, new calculations of the acoustic wave energy fluxes generated in the solar convective zone was performed. The original theory developed was corrected by including a new frequency factor describing temporal variations of the turbulent energy spectrum. We have modified the original Stein code by including this new frequency factor, and tested the code extensively. Another possible source of the mechanical energy generated in the solar convective zone is the excitation of magnetic flux tube waves which can carry energy along the tubes far away from the region. The problem as to how efficiently those waves are generated in the Sun was recently solved. The propagation of nonlinear magnetic tube waves in the solar atmosphere was calculated, and mode coupling, shock formation, and heating of the local medium was studied. The wave trapping problems and evaluation of critical frequencies for wave reflection in the solar atmosphere was studied. It was shown that the role played by Alfven waves in the wind accelerations and the coronal hole heating is dominant. Presently, we are performing calculations of wave energy fluxes generated in late-type dwarf stars and studying physical processes responsible for the heating of stellar chromospheres and coronae. In the area of physics of waves, a new analytical approach for studying linear Alfven waves in smoothly nonuniform media was recently developed. This approach is presently being extended to study the propagation of linear and nonlinear magnetohydrodynamic (MHD) waves in stratified, nonisothermal and solar atmosphere. The Lighthill theory of sound generation to nonisothermal media (with a special temperature distribution) was extended. Energy cascade by nonlinear MHD waves and possible chaos driven by these waves are presently considered.

Musielak, Z. E.↗
NASA NTRS1992

Low power arcjet test facility impacts

Performance characterization of a flight-type 1.4 kW arcjet system were conducted at the Rocket Research Company (RRC) in Redmond, WA, and at the NASA LeRC in Cleveland, OH. The objectives of these tests were as follows: to compare low-power arcjet performance at two different test facilities; to compare arcjet performance obtained with a 2:1 mixture of gaseous hydrogen and nitrogen and hydrazine; and to quantify the effects of test cell pressure on thruster operating characteristics. Performance and thruster temperature distributions were measured at thruster input power levels and propellant mass flow rates ranging from 1274 to 1370 W and from 3.2 x 10(exp -5) to 5.1 x 10(exp -5) kg/s, respectively. Specific impulses measured at the two facilities, at comparable test cell pressures, using gaseous hydrogen-nitrogen propellant mixtures agreed to within 1 percent over the range of operating conditions tested. The specific impulses measured using hydrazine propellant were higher than that for the cold hydrogen-nitrogen mixtures. Agreement between by hydrazine and gas mixture data was good, however, when the differences in propellant enthalpies at the thruster inlet were considered. Specific impulse showed a strong dependence on test facility pressure, and was 3 to 4 percent higher below 0.1 Pa than for test cell pressures above 5 Pa.

Morren, W. Earl↗