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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Surface fitting three-dimensional bodies

The geometry of general three-dimensional bodies was generated from coordinates of points in several cross sections. Since these points may not be on smooth curves, they are divided into groups forming segments and general conic sections are curve fit in a least-squares sense to each segment of a cross section. The conic sections are then blended in the longitudinal direction through longitudinal curves. Both the cross-sectional and longitudinal curves may be modified by specifying particular segments as straight lines or specifying slopes at selected points. This method was used to surface fit a 70 deg slab delta wing and the HL-10 Lifting Body. The results for the delta wing were very close to the exact geometry. Although there is no exact solution for the lifting body, the surface fit generated a smooth surface with cross-sectional planes very close to prescribed coordinate points.

Dejarnette, F. R.↗
NASA NTRS1983

Thermal behavior of laboratory models of honeycomb-covered solar ponds

Laboratory experiments were conducted to provide insight into the technical feasibility of honeycomb-covered solar ponds. Cooling tests using honeycomb panels of various materials and geometries showed that a 5.7-cm-thick one-tier panel insulated as effectively as a 10-cm fiberglass slab. Heating tests demonstrated that a model pond covered with a polycarbonate panel boiled upon 16 hours of continuous exposure to a 150-W spotlight. Analysis of the experimental data indicates positively that honeycomb-covered solar ponds can be expected to perform satisfactorily, and that larger-scale outdoor tests should be conducted to provide a more realistic assessment and a more refined performance estimate.

Lin, E. I. H.↗
NASA NTRS1993

Nongray gas analyses for reflecting walls utilizing a flux technique

A flux formulation for a planar slab of molecular gas radiation bounded by diffuse reflecting walls is developed. While this formulation is limited to the planar geometry, it is useful for studying approximations necessary in modeling nongray radiative heat transfer. The governing equations are derived by considering the history of multiple reflections between the walls. Accurate solutions are obtained by explicitly accounting for a finite number of reflections and approximating the spectral effects of the remaining reflections. Four approximate methods are presented and compared using a single absorption band of H2O. All four methods reduce to an identical zeroth-order formulation, which accounts for all reflections approximately but does handle nonreflected radiation correctly. A single absorption band of CO2 is also considered using the best-behaved approximation for higher orders. A zeroth-order formulation is sufficient to predict the radiative transfer accurately for many cases considered. For highly reflecting walls, higher order solutions are necessary for better accuracy. Including all the important bands of H2O, the radiative source distributions are also obtained for two different temperature and concentration profiles.

Menart, J. A.↗
NASA NTRS1972

The estimation of galactic cosmic ray penetration and dose rates

This study is concerned with approximation methods that can be readily applied to estimate the absorbed dose rate from cosmic rays in rads - tissue or rems inside simple geometries of aluminum. The present work is limited to finding the dose rate at the center of spherical shells or behind plane slabs. The dose rate is calculated at tissue-point detectors or for thin layers of tissue. This study considers cosmic-rays dose rates for both free-space and earth-orbiting missions.

Burrell, M. O.↗
NASA NTRS1989

Resolution experiments for NW Pacific subduction zone tomography

Results are reported from an investigation of the resolving power of ISC/NEIC P travel-time data in tomographic inversions for the geometry of the subduction zones in the NW Pacific. From thermal models for the Kurile, Janan, Izu-Bonin, Mariana, and Ryukyu slabs, three-dimensional synthetic velocity anomalies for subducting slabs are generated and projected onto a cell model for the uppermost 1400 km of the mantle. These synthetic models are used to compute synthetic delay times for ray paths corresponding to the source and receiver locations used for the actual data, add Gaussian noise, invert the synthetic data, and compare the resulting velocity structure to the initial synthetic models. This comparison is illustrated for sections through the Kuriles and the Mariana arcs. A variety of resolution artifacts are observed, which in many cases resemble features visible in the tomographic results obtained from inverting the actual ISC/NEIC data.

Spakman, Wim↗
NASA NTRS1996

Combustion Processes in Hybrid Rocket Engines

In recent years, there has been a resurgence of interest in the development of hybrid rocket engines for advanced launch vehicle applications. Hybrid propulsion systems use a solid fuel such as hydroxyl-terminated polybutadiene (HTPB) along with a gaseous/liquid oxidizer. The performance of hybrid combustors depends on the convective and radiative heat fluxes to the fuel surface, the rate of pyrolysis in the solid phase, and the turbulent combustion processes in the gaseous phases. These processes in combination specify the regression rates of the fuel surface and thereby the utilization efficiency of the fuel. In this paper, we employ computational fluid dynamics (CFD) techniques in order to gain a quantitative understanding of the physical trends in hybrid rocket combustors. The computational modeling is tailored to ongoing experiments at Penn State that employ a two dimensional slab burner configuration. The coordinated computational/experimental effort enables model validation while providing an understanding of the experimental observations. Computations to date have included the full length geometry with and with the aft nozzle section as well as shorter length domains for extensive parametric characterization. HTPB is sed as the fuel with 1,3 butadiene being taken as the gaseous product of the pyrolysis. Pure gaseous oxygen is taken as the oxidizer. The fuel regression rate is specified using an Arrhenius rate reaction, which the fuel surface temperature is given by an energy balance involving gas-phase convection and radiation as well as thermal conduction in the solid-phase. For the gas-phase combustion, a two step global reaction is used. The standard kappa - epsilon model is used for turbulence closure. Radiation is presently treated using a simple diffusion approximation which is valid for large optical path lengths, representative of radiation from soot particles. Computational results are obtained to determine the trends in the fuel burning or regression rates as a function of the head-end oxidizer mass flux, G=rho(e)U(e), and the chamber pressure. Furthermore, computation of the full slab burner configuration has also been obtained for various stages of the burn. Comparisons with available experimental data from small scale tests conducted by General Dynamics-Thiokol-Rocketdyne suggest reasonable agreement in the predicted regression rates. Future work will include: (1) a model for soot generation in the flame for more quantitative radiative transfer modelling, (2) a parametric study of combustion efficiency, and (3) transient calculations to help determine the possible mechanisms responsible for combustion instability in hybrid rocket motors.

Venkateswaran,S.↗
NASA NTRS1976

Si II lines in the shell of Zeta Tau

Non-LTE strengths of Si II lines were computed in an effort to reproduce the observed strengths of Si II lines in the shell spectrum of Zeta Tau. This effort was unsuccessful, probably because it assumed that the shell could be represented by a finite, plane-parallel slab. The main conclusion of this study, then, is that in order to understand the shell spectra of Be stars, a more realistic geometry must be assumed, in which the shell is represented by a thick disk.

Heap, S. R.↗
NASA NTRS1985

Solar-pumped solid state Nd lasers

Solid state neodymium lasers are considered candidates for space-based polar-pumped laser for continuous power transmission. Laser performance for three different slab laser configurations has been computed to show the excellent power capability of such systems if heat problems can be solved. Ideas involving geometries and materials are offered as potential solutions to the heat problem.

Williams, M. D.↗
NASA NTRS1990

Analytical solutions with Generalized Impedance Boundary Conditions (GIBC)

The diffraction by a material discontinuity in a thick dielectric/ferrite layer is considered by modeling the layer as a distributed current sheet obeying generalized sheet transition conditions (GSTC's). The sheet currents are then formulated and solved via the standard dual integral equation approach. This yields the diffracted field in terms of unknown constants which underscore the non-uniqueness of the GSTC current sheet representation. The constants are dependent on the geometry and properties of the discontinuity and are determined by enforcing field continuity across the material junction. This requires the field internal to the slab which are determined from the external ones via analytic continuity. Results are given which validate the solution and demonstrate the importance of the constants.

Ricoy, Mark A.↗
NASA NTRS1984

A critical assessment of viscous models of trench topography and corner flow

Stresses for Newtonian viscous flow in a simple geometry (e.g., corner flow, bending flow) are obtained in order to study the effect of imposed velocity boundary conditions. Stress for a delta function velocity boundary condition decays as 1/R(2); for a step function velocity, stress goes as 1/R; for a discontinuity in curvature, the stress singularity is logarithmic. For corner flow, which has a discontinuity of velocity at a certain point, the corresponding stress has a 1/R singularity. However, for a more realistic circular-slab model, the stress singularity becomes logarithmic. Thus the stress distribution is very sensitive to the boundary conditions, and in evaluating the applicability of viscous models of trench topography it is essential to use realistic geometries. Topography and seismicity data from northern Hoshu, Japan, were used to construct a finite element model, with flow assumed tangent to the top of the grid, for both Newtonian and non-Newtonian flow (power law 3 rheology). Normal stresses at the top of the grid are compared to the observed trench topography and gravity anomalies. There is poor agreement. Purely viscous models of subducting slables with specified velocity boundary conditions do not predict normal stress patterns compatible with observed topography and gravity. Elasticity and plasticity appear to be important for the subduction process.

Zhang, J.↗
NASA NTRS1985

A critical assessment of viscous models of trench topography and corner flow

Stresses for Newtonian viscous flow in a simple geometry (e.g., corner flow, bending flow) are obtained in order to study the effect of imposed velocity boundary conditions. Stress for a delta function velocity boundary condition decays as 1/R(2); for a step function velocity, stress goes as 1/R; for a discontinuity in curvature, the stress singularity is logarithmic. For corner flow, which has a discontinuity of velocity at a certain point, the corresponding stress has a 1/R singularity. However, for a more realistic circular-slab model, the stress singularity becomes logarithmic. Thus the stress distribution is very sensitive to the boundary conditions, and in evaluating the applicability of viscous models of trench topography it is essential to use realistic geometries. Topography and seismicity data from northern Hoshu, Japan, were used to construct a finite element model, with flow assumed tangent to the top of the grid, for both Newtonian and non-Newtonian flow (power law 3 rheology). Normal stresses at the top of the grid are compared to the observed trench topography and gravity anomalies. There is poor agreement. Purely viscous models of subducting slables with specified velocity boundary conditions do not predict normal stress patterns compatible with observed topography and gravity. Elasticity and plasticity appear to be important for the subduction process.

Zhang, J.↗
NASA NTRS1993

Magnetohydrodynamic wave propagation in one-dimensional nonhomogeneous, self-gravitating clouds

We study the propagation of magnetohydrodynamic (MHD) waves through nonhomogeneous, selfgravitating, magnetic media representative of molecular cloud environments and focus on the issues of cloud support and line profiles. Since the general treatment of this topic is burdened by a complex mathematical formalism, we consider simplifying geometries which yield analytical solutions in the linear wave limit. In particular, we study both magnetoacoustic and Alfven wave propagation along the density gradient in a one-imensional slab. Of specific relevance to molecular clouds, we find that the back reaction of the Alfven waves can provide a pressure along the direction of the magnetic field lines; this pressure can help support a density enhancement against gravitational collapse. Furthermore, we find that the velocity amplitudes of these waves increase as the density decreases, in rough agreement with observational estimates of line width versus density relations.

Fatuzzo, Marco↗
NASA NTRS1989

Energy dissipation of Alfven wave packets deformed by irregular magnetic fields in solar-coronal arches

The importance of field line geometry for shear Alfven wave dissipation in coronal arches is demonstrated. An eikonal formulation makes it possible to account for the complicated magnetic geometry typical in coronal loops. An interpretation of Alfven wave resonance is given in terms of gradient steepening, and dissipation efficiencies are studied for two configurations: the well-known slab model with a straight magnetic field, and a new model with stochastic field lines. It is shown that a large fraction of the Alfven wave energy flux can be effectively dissipated in the corona.

Similon, Philippe L.↗
NASA NTRS1978

Inlet boundary-layer shapes on four aircraft forebodies at Mach 6

Boundary-layer shape measurements at the engine inlet on four different hypersonic aircraft forebody designs (with no engine on the forebody) are reported. The measurements provide a qualitative assessment of the effectiveness of various forebody geometries as engine inlet precompression surfaces. The designs, tested in a hypersonic tunnel at Mach 6 and a nominal freestream Reynolds number of 30,500,000, included a semiconical forebody, a configuration similar to a slab delta wing, a conical nose blended into a flat surface, and a conical, complex forebody shape. Boundary layer height as a function of forebody compression is shown for each design.

Lawing, P. L.↗
NASA NTRS1972

Heat pipe design handbook, part 2

The utilization of a digital computer code for heat pipe analysis and design (HPAD) is described which calculates the steady state hydrodynamic heat transport capability of a heat pipe with a particular wick configuration, the working fluid being a function of wick cross-sectional area. Heat load, orientation, operating temperature, and heat pipe geometry are specified. Both one 'g' and zero 'g' environments are considered, and, at the user's option, the code will also perform a weight analysis and will calculate heat pipe temperature drops. The central porous slab, circumferential porous wick, arterial wick, annular wick, and axial rectangular grooves are the wick configurations which HPAD has the capability of analyzing. For Vol. 1, see N74-22569.

Skrabek, E. A.↗
NASA NTRS1984

Solidification interface shape for continuous casting in an offset mold - Two analytical methods

A solution method for finding the unknown solidification interface in manufacturing slab ingots as a continuous casting is presented, which involves a product solution in the potential plane and the use of conjugate harmonic functions. It is argued that the method may be more direct for some geometries than the Cauchy boundary value method. Moreover, the usefulness of the Cauchy boundary value method is demonstrated through the example of a nonsymmetric horizontal mold where the walls are offset to support the lower ingot boundary.

Siegel, R.↗
NASA NTRS2005

4-Pass Pumping of Nd+3:YAG Slabs

A solid-state, side pumping scheme, designed to enhance pump energy absorption, has been adapted for use in small, side-pumped, Nd+3:YAG zigzag lasers. This technique allows for pump radiation to make four complete passes through the gain medium, effectively doubling the absorption length of the usual 2-pass geometry. This produces higher inversion densities, higher gains, broader operating temperature bands and overall higher efficiencies. The improved performance has been demonstrated with a small Nd+3:YAG, mJ-class oscillator, and will aid in the development for space-based remote sensing laser transmitters for altimetry and mapping instruments.

Coyle, D. Barry↗
NASA NTRS1990

Application of the LAURA code for slender-vehicle aerothermodynamics

Application of a three-dimensional thin-layer Navier-Stokes code (LAURA) to compute the laminar, perfect gas aerothermodynamics of slender vehicles is demonstrated. Comparison of solutions with experimental data enabled an assessment of the code's aerodynamic heating prediction capabilities. The results show radial grid refinement to a wall cell Reynolds number of 2 to be accurate for predicting aerodynamic heating to a slender cone. Additional comparisons for an 80 deg slab-delta wing and a generic Aero-Space Plane vehicle show the method to be generally accurate using this radial cell spacing. Discrepancies between the predicted and measured heating in a region of crossflow separation on the Aero-Space Plane geometry are noted which indicates the need for further study. While additional applications and comparisons are required to fully test the LAURA program, the results of this study demonstrate the current level of confidence and the engineering utility of this particular code.

Thompson, Richard A.↗