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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 1,585 records · Page 88
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NASA NTRS1991

The temperature of the circumstellar envelope of Alpha Orionis

The processes that heat and cool the circumstellar envelope of Alpha Ori are analyzed and the temperature calculated as a function of distance from the star. Cooling by fine structure lines is included for the first time in a general way in the theory of the thermal balance of a circumstellar envelope. Adiabatic cooling, dust-drag heating, and various line coolants contribute in the outer envelope, whereas the fine structure lines of O I and Si II and adiabatic cooling are dominant in the inner envelope. The rotational levels of CO cool the gas only at very small and at very large distances; elsewhere they provide a small amount of heating. The temperature declines very rapidly at first and then varies roughly as r exp -1/2 in the outer envelope. At very large distances, the temperature distribution flattens out due to photoelectron heating and reaches a minimum of about 4 K at about 250 arcsec.

Rodgers, Bernadette↗
NASA NTRS1992

Finite difference solution for transient cooling of a radiating-conducting semitransparent layer

Transient solutions were obtained for cooling a semitransparent material by radiation and conduction. The layer is in a vacuum environment so the only means for heat dissipation is by radiation from within the medium leaving through the boundaries. Heat conduction serves only to partially equalize temperatures across the layer. As the optical thickness is increased, steep temperature gradients exist near the boundaries when conduction is relatively small. A solution procedure is required that will provide accurate temperature distributions adjacent to the boundaries, or radiative heat losses will be in error. The approach utilized numerical Gaussian integration to obtain the local radiative source term, and a finite difference procedure with variable space and time increments to solve the transient energy equation.

Siegel, Robert↗
NASA NTRS1991

Error analysis of image reconstruction by a synthetic aperture interferometric radiometer

An error analysis is presented for the image reconstruction algorithm currently employed by the electronically steered thinned array radiometer aircraft instrument. This instrument samples components of the Fourier transform of the brightness temperature distribution at 1.4 GHz. Sources of error are identified, including systematic offsets and stochastic noise in the measurements, errors in the interference pattern antenna calibration, multipath scattering from the antenna support structure, mutual coupling between nearby array elements, and variations in the antenna patterns of the array elements. These errors are shown to produce artifacts in the image which appear as 'streaks' running along the instrument flight line. Possible hardware corrections are discussed. These include a reduction in the profile of the antenna support structure and a decoupling of adjacent and other nearby array elements using corrugated 'skirts'. Also discussed are several image enhancement techniques which detect and correct for some of the streaking. These techniques include a renormalization of the interference patterns based on the measured element patterns, a perturbation based interpretation of image contrast, and a covariance analysis of noise present in the image.

Ruf, Christopher S.↗
NASA NTRS1992

Studies of the effects of curvature on dilution jet mixing

An analytical program was conducted using both three-dimensional numerical and empirical models to investigate the effects of transition liner curvature on the mixing of jets injected into a confined crossflow. The numerical code is of the TEACH type with hybrid numerics; it uses the power-law and SIMPLER algorithms, an orthogonal curvilinear coordinate system, and an algebraic Reynolds stress turbulence model. From the results of the numerical calculations, an existing empirical model for the temperature field downstream of single and multiple rows of jets injected into a straight rectangular duct was extended to model the effects of curvature. Temperature distributions, calculated with both the numerical and empirical models, are presented to show the effects of radius of curvature and inner and outer wall injection for single and opposed rows of cool dilution jets injected into a hot mainstream flow.

Holdeman, James D.↗
NASA NTRS1992

CW dye laser technique for simultaneous, spatially-resolved measurements of temperature, pressure, and velocity of NO in an underexpanded free jet

Gas dynamic quantities within an underexpanded free jet were measured nonintrusively using a rapid-tuning, CW ring dye laser. A nitrogen jet was seeded with 0.5 percent NO in N2, and the conditions were controlled such that a barrel shock formed. The frequency-doubled output of the dye laser was used to spectrally resolve rotational lines in the NO gamma band near 225 nm. With the rapid-tuning capability, these rotational spectra were acquired at a repetition rate of 4 kHz. Spatial resolution was afforded by monitoring the induced fluorescence via a lens and photomultiplier tube. Modeling the spectrally-resolved features with Voigt profiles permitted simultaneous measurements of NO velocity, rotational temperature, and pressure. Expansion of the jet was assumed to be isentropic, and agreement between measured and expected values was typically better than 10 percent over most of the Mach-number range encountered. At high Mach numbers, the measured rotational temperatures systematically departed from the isentropic temperature distribution. Such a measured departure could be ascribed to the onset of a non-Boltzmann distribution of NO rotational states.

Di Rosa, M. D.↗
NASA NTRS1992

Effects of equatorially trapped ions on refilling of the plasmasphere

The kinetic aspects of shock formation in response to the equatorial heating of ions are reported by means of small-scale kinetic simulations of countersteaming plasma flows along a spatially varying magnetic field having the features of the dipolar magnetic field lines. Attention is given to the trapping of the field-aligned flowing ions in response to the simulated equatorial heating of ions and the associated self-consistent structures in the electric potentials and the f-plasma flow pattern. Trapping is found to lead to the formation of electrostatic shocks, which propagate away from the 'equator' as seen in the hydrodynamic model of Singh and Torr (1990). The shocks form near the mirror points of the 'equatorially' heated ions. The second stage of the refilling with equatorially trapped ions is reported. A variety of structures in density and temperature distributions as the refilling proceeds slowly is found.

Singh, Nagendra↗
NASA NTRS1992

Simulation of the zonal mean climatology of the middle atmosphere with a three-dimensional spectral model for solstice and equinox conditions

A 3D spectral model was used to simulate the zonal mean state of the middle atmosphere for solstice and equinox conditions. The model incorporates realistic parameterizations of atmospheric infrared cooling and a gravity wave formulation based on a combination of Lindzen's (1981) and Matsuno's (1982) approaches. The temperature distributions for both seasons and the zonal wind distribution for solstice are found to be in satisfactory agreement with the empirical model of Fleming et al. (1988). Net vertical fluxes of horizontal momentum are in good agreement with systematic observations of gravity waves in the middle atmosphere.

Akmaev, R. A.↗
NASA NTRS1992

Heat transfer and fluid flow in floating-zone crystal growth with a mostly covered melt surface

Computer simulation was conducted to study a modified floating-zone crystal growth process, in which the melt surface is mostly covered with a heated ring. The growth of 6-mm diameter single crystals of NaNO3 was considered, and the effects of the following parameters were studied: (1) temperature of the ring, (2) growth rate, (3) surface tension-temperature coefficient of the melt, (4) thermal expansion coefficient of the melt, and (5) gravity. It was demonstrated that thermocapillary convection in the melt zone is reduced significantly in this modified process. The model was checked against the measured lengths of the meniscus near the growth front and axial temperature distribution in a growing crystal, and the agreement was good.

Lan, C. W.↗
NASA NTRS1992

Infrared thermographic analysis of polymer composites during ballistic impact

An infrared thermographic system was used to measure the surface temperature profile of composite materials under ballistic impact. The heat deposited was calculated based on the temperature profiles. The extent of damage induced in the materials was determined qualitatively from the measured data. The relative contribution of frictional heat to total energy absorption was evaluated, and the effect of the shape of the projectile on the extent of damage and temperature distribution in the composites was examined. The results show that graphite and polyethylene composite are more effective than Kevlar composite in dissipating heat during the ballistic impact penetration process due to their higher thermal conductivity.

Hsieh, C. Y.↗
NASA NTRS1992

Transient pool boiling in microgravity

Transient nucleate pool boiling experiments using R113 are conducted for short times in microgravity and in earth gravity with different heater surface orientations and subcoolings. The heating surface is a transparent gold film sputtered on a quartz substrate, which simultaneously provides surface temperature measurements and permits viewing of the boiling process from beneath. For the microgravity experiments, which have uniform initial temperatures and no fluid motion, the temperature distribution in the R 113 at the moment of boiling inception is known. High speed cameras with views both across and through the heating surface record the boiling spread across the heater surface, which is classified into six distinct categories.

Ervin, J. S.↗
NASA NTRS1992

Twenty-five years of aerodynamic research with infrared imaging

A review is presented of the commercial introduction of IR imaging systems in the midsixties that has opened the possibilities to visualize viscous interactions between a body and the surrounding airflow by mapping the surface temperature distributions on configurations of interest. The capability of IR imaging systems to produce in real-time thermograms, which can be interpreted both locally and globally, makes them useful for heat transfer and skin-friction aerodynamic studies. Attention is given to IR systems and data processing, supersonic and hypersonic studies, Space Shuttle flight experiments, subsonic and transonic studies, and propulsion studies.

Gartenberg, Ehud↗
NASA NTRS1992

Finite element nonlinear panel flutter with arbitrary temperatures in supersonic flow

A finite element frequency domain method for predicting nonlinear flutter response of panels with temperature effects is presented. By using the principle of virtual work, the element nonlinear stiffness formulation for a panel under a combined thermal and aerodynamic loads is derived on the bases of von Karman's large deflection plate theory, the first-order piston theory aerodynamics and the quasi-steady thermal stress theory. The system equations of motion can be mathematically separated into two sets of equations and then solved in sequence. The first set of equations yields the panel thermal-aerodynamic equilibrium and the second set of equations of motion leads to the flutter limit-cycle oscillations. Stability and flutter boundaries can also be obtained from the two sets of system equations. Finite element large amplitude limit-cycle flutter results at different uniform temperatures are obtained for a simply supported square panel and are compared with existing Galerkin/time integration and other finite element solutions. Effects of nonuniform temperature distributions, panel length-to-width ratios, and boundary conditions on flutter responses of rectangular and triangular panels are presented.

Xue, David Y.↗
NASA NTRS1992

Solution strategies and heat transfer calculations for three-dimensional configurations at hypersonic speeds

A procedure which reduces the memory requirements for computing the viscous flow over a modified Orbiter geometry at a hypersonic flight condition is presented. The Langley Aerothermodynamic Upwind Relaxation Algorithm (LAURA) code which incorporates a thermochemical nonequilibrium chemistry model, a finite rate catalytic wall boundary condition and wall temperature distribution based on radiation equilibrium is used in this study. In addition, the effect of choice of 'min mod' function, eigenvalue limiter and grid density on surface heating is investigated. The surface heating from a flowfield calculation at Mach number 22, altitude of 230,000 ft and 40 deg angle of attack is compared with flight data from three Orbiter flights.

Weilmuenster, K. J.↗
NASA NTRS1992

Characteristics of the Shuttle Orbiter leeside flow during a reentry condition

A study of the leeside flow characteristics of the Shuttle Orbiter is presented for a reentry flight condition. The flow is computed using a point-implicit, finite-volume scheme known as the Langley Aerothermodynamic Upwind Relaxation Algorithm (LAURA). LAURA is a second-order accurate, laminar Navier-Stokes solver, incorporating finite-rate chemistry with a radiative equilibrium wall temperature distribution and finite-rate wall catalysis. The resulting computational solution is analyzed in terms of salient flow features and the surface quantities are compared with flight data.

Kleb, William L.↗
NASA NTRS1991

Measurements of the effects of thermal contact resistance on steady state heat transfer in phosphoric-acid fuel cell stack

The influence of the thermal contact resistance on the heat transfer between the electrode plates, and the cooling system plate in a phosphoric-acid fuel-cell stack was experimentally investigated. The investigation was conducted using a set-up that simulates the operating conditions prevailing in a phosphoric acid fuel-cell stack. The fuel-cell cooling system utilized three types of coolants, water, engine oil, and air, to remove excess heat generated in the cell electrode and to maintain a reasonably uniform temperature distribution in the electrode plate. The thermal contact resistance was measured as a function of pressure at the interface between the electrode plate and the cooling system plate. The interface pressure range was from 0 kPa to 3448 kPa, while the Reynolds number for the cooling limits varied from 15 to 79 for oil, 1165 to 6165 for water, and 700 to 6864 for air. Results showed that increasing the interface pressure resulted in a higher heat transfer coefficient.

Abdul-Aziz, Ali↗
NASA NTRS1992

Low-power arcjet test facility impacts

Performance characterizations of a flight-type 1.4 kW arcjet system were conducted. 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 the hydrazine and gas mixture data was good, however, when the differences in propellant ethalpies 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. E.↗
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 NTRS1993

Coupled multi-disciplinary composites behavior simulation

The capabilities of the computer code CSTEM (Coupled Structural/Thermal/Electro-Magnetic Analysis) are discussed and demonstrated. CSTEM computationally simulates the coupled response of layered multi-material composite structures subjected to simultaneous thermal, structural, vibration, acoustic, and electromagnetic loads and includes the effect of aggressive environments. The composite material behavior and structural response is determined at its various inherent scales: constituents (fiber/matrix), ply, laminate, and structural component. The thermal and mechanical properties of the constituents are considered to be nonlinearly dependent on various parameters such as temperature and moisture. The acoustic and electromagnetic properties also include dependence on vibration and electromagnetic wave frequencies, respectively. The simulation is based on a three dimensional finite element analysis in conjunction with composite mechanics and with structural tailoring codes, and with acoustic and electromagnetic analysis methods. An aircraft engine composite fan blade is selected as a typical structural component to demonstrate the CSTEM capabilities. Results of various coupled multi-disciplinary heat transfer, structural, vibration, acoustic, and electromagnetic analyses for temperature distribution, stress and displacement response, deformed shape, vibration frequencies, mode shapes, acoustic noise, and electromagnetic reflection from the fan blade are discussed for their coupled effects in hot and humid environments. Collectively, these results demonstrate the effectiveness of the CSTEM code in capturing the coupled effects on the various responses of composite structures subjected to simultaneous multiple real-life loads.

Singhal, Surendra N.↗