SEARCH · Engineering Papers

Results for “multiphase”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3

All sources NASA NTRS DOE OSTI

NASA NTRS1979

Landsat-based multiphase estimation of California's irrigated lands

Currently, inventory of California's irrigated lands is performed on a seven year cycle. Since 1975, the University of California in cooperation with NASA and the California Department of Water Resources has been developing and testing techniques to utilize a Landsat based remote sensing system to produce statewide estimates in a single year. The proposed system utilizes multiphase sampling, stratification and multitemporal Landsat imagery to produce the estimate. Early research concentrated on regional estimates to develop the techniques. This year, an inventory of the entire state of California is being performed. In addition, research on the utilization of digital analysis for estimating irrigated acreage and the determination of specific crop types (manual and digital analysis) is also underway.

Wall, S. L.↗

NASA NTRS1982

Improved uniformity of multiphase ceramic-metal plasma-sprayed coats

Processing-technology development of a multiphase, self-lubricating, plasma-spray powder resulted in greater uniformity and reproducibility of plasma-sprayed coats. The effect of particle-size variation, binder concentration, and reproducible processing parameters are reported. Greater adhesive strengths of coats to substrates were achieved by particle-size variation, use of an intermediate bond coat such as Ni-Cr, or heat treatment. Quantitative analyses of polished, coated specimens are also given.

Nakamura, H. H.↗

NASA NTRS1984

Modelling the Local Interstellar Medium as a Supernova Remnant in a Multiphase Gas

The construction of supernova remnant which is consistent with the observations and what it talls about the theory was investigated. It is argued that thermal evaporation and local inhomogeneity are crucial elements which are essential to any satisfactory description. It is concluded that: (1) a multiphase supernova remnant (SNR) seems to provide a plausible description of the local interstellar medium (ISM); (2) the local region could have been deficient in cool gas prior to the supernova both on theoretical and observational grounds; (3) the Sun may lie in a region towards the outside of the supernova remnant which hasn't yet come into pressure equilibrium with the hot gas; and (4) evaporative models give a much more satisfactory description of the O VI observations than Sedov Solutions.

Cowie, L. L.↗

NASA NTRS1988

The application of single particle hydrodynamics in continuum models of multiphase flow

A review of the application of single particle hydrodynamics in models for the exchange of interphase momentum in continuum models of multiphase flow is presented. Considered are the equations of motion for a laminar, mechanical two phase flow. Inherent to this theory is a model for the interphase exchange of momentum due to drag between the dispersed particulate and continuous fluid phases. In addition, applications of two phase flow theory to de-mixing flows require the modeling of interphase momentum exchange due to lift forces. The applications of single particle analysis in deriving models for drag and lift are examined.

Decker, Rand↗

NASA NTRS1989

A programmable CCD driver circuit for multiphase CCD operation

A programmable CCD (charge-coupled device) driver circuit was designed to drive CCDs in multiphased modes. The purpose of the drive electronics is to operate developmental CCD imaging arrays for NASA's tiltable moderate resolution imaging spectrometer (MODIS-T). Five objectives for the driver were considered during its design: (1) the circuit drives CCD electrode voltages between 0 V and +30 V to produce reasonable potential wells, (2) the driving sequence is started with one input signal, (3) the driving sequence is started with one input signal, (4) the circuit allows programming of frame sequences required by arrays of any size, (5) it produces interfacing signals for the CCD and the DTF (detector test facility). Simulation of the driver verified its function with the master clock running up to 10 MHz. This suggests a maximum rate of 400,000 pixels/s. Timing and packaging parameters were verified. The design uses 54 TTL (transistor-transistor logic) chips. Two versions of hardware were fabricated: wirewrap and printed circuit board. Both were verified functionally with a logic analyzer.

Ewin, Audrey J.↗

NASA NTRS1990

Microstructure and mechanical properties of multiphase NiAl-based alloys

The effect of the gamma-prime phase on the deformation behavior and fracture resistance of melt-spun ribbons and consolidated bulk specimens of a series of Nial-based alloys with Co and Hf additions has been examined. The morphology, location, and volume fraction of the gamma-prime phase are significant factors in enhancing the fracture resistance of the normally brittle NiAl-based alloys. In particular, the results indicate that a continuous-grain-boundary film of gamma-prime can impart limited room-temperature ductility regardless of whether B2 or L10 NiAl is present. Guidelines for microstructure control in multiphase NiAl-based alloys are also presented.

Pank, D. R.↗

NASA NTRS1990

Atomization modeling in a multiphase flow environment and comparison with experiments

An atomization model based on Reitz's instability wave analysis has been implemented into the ARICC3D multiphase CFD combustion code. Preliminary test runs with cold non-evaporating liquid jet and coaxial gas-liquid atomization cases appeared to have verified basic performance of the model, generating realistic-looking sprays. Furthermore, the extended liquid jet is explicitly resolved, and predicted jet lengths agree well with classical correlations. Fair agreement with test data is obtained for predicted spray tip penetrations and liquid mass flux radial distributions, with obvious room for improvement. Some numerical problems also appear to have resulted with the current implementation when low gas Mach number and high liquid velocities are involved.

Liang, P. Y.↗

NASA NTRS1991

Ram-pressure stripping of the multiphase interstellar medium of the Virgo cluster elliptical galaxy M86 (NGC 4406)

The available infrared, optical, and X-ray data on the elliptical galaxy M86, which is experiencing strong ram-pressure stripping in the intracluster medium of the Virgo Cluster, are analyzed. A significant component of infrared 60 micron emission displaced from the center of the galaxy is found. The displaced 60 micron emission lies on the optical major axis of the galaxy in the direction of perturbations to the optical isophotes and is coincident with a small feature in X-ray emission southwest of the X-ray plume. The displaced infrared emission is interpreted in terms of collisionally heated dust exposed to hot gas where ram pressure and turbulence are disrupting the stripped interstellar medium of the galaxy. The displacement of the outer optical isophotes in the direction of the stripped gas in suggested to be due to reflection of star-light on the dust grains. Ram pressure has separated and exposed the various components of the multiphase interstellar medium of M86, enabling these constituents to be identified and analyzed separately for the first time in an elliptical galaxy.

White, David A.↗

NASA NTRS1991

A computer code for multiphase all-speed transient flows in complex geometries. MAST version 1.0

The operation of the MAST code, which computes transient solutions to the multiphase flow equations applicable to all-speed flows, is described. Two-phase flows are formulated based on the Eulerian-Lagrange scheme in which the continuous phase is described by the Navier-Stokes equation (or Reynolds equations for turbulent flows). Dispersed phase is formulated by a Lagrangian tracking scheme. The numerical solution algorithms utilized for fluid flows is a newly developed pressure-implicit algorithm based on the operator-splitting technique in generalized nonorthogonal coordinates. This operator split allows separate operation on each of the variable fields to handle pressure-velocity coupling. The obtained pressure correction equation has the hyperbolic nature and is effective for Mach numbers ranging from the incompressible limit to supersonic flow regimes. The present code adopts a nonstaggered grid arrangement; thus, the velocity components and other dependent variables are collocated at the same grid. A sequence of benchmark-quality problems, including incompressible, subsonic, transonic, supersonic, gas-droplet two-phase flows, as well as spray-combustion problems, were performed to demonstrate the robustness and accuracy of the present code.

Chen, C. P.↗

NASA NTRS1994

Micromechanical analysis of thermo-inelastic multiphase short-fiber composites

A micromechanical formulation is presented for the prediction of the overall thermo-inelastic behavior of multiphase composites which consist of short fibers. The analysis is an extension of the generalized method of cells that was previously derived for inelastic composites with continuous fibers, and the reliability of which was critically examined in several situations. The resulting three dimensional formulation is extremely general, wherein the analysis of thermo-inelastic composites with continuous fibers as well as particulate and porous inelastic materials are merely special cases.

Aboudi, Jacob↗

NASA NTRS1998

Micromechanical Prediction of the Effective Coefficients of Thermo-Piezoelectric Multiphase Composites

The micromechanical generalized method of cells model is employed for the prediction of the effective elastic, piezoelectric, dielectric, pyroelectric and thermal-expansion constants of multiphase composites with embedded piezoelectric materials. The predicted effective constants are compared with other micromechanical methods available in the literature and good agreements are obtained.

Aboudi, Jacob↗

NASA NTRS1996

Effects of Gravity and Shear on the Dynamics and Stability of Particulate and Multiphase Flows

The main objectives of this project are to understand the differing particulate and multiphase flow behaviors that will occur in space and in Earth's gravity. More specifically, the project is concerned with understanding the effect of shear and gravity on two relatively ideal suspensions with significant inertial effects. The first is a gas-solid suspension at small Reynolds numbers and finite Stokes numbers. In this type of suspensions the inertia of the particle phase is significant while the hydrodynamic interactions are dominated by viscous forces in the suspending fluid. The other is a bubble suspension at small Weber and large Reynolds numbers. The hydrodynamic interactions in such suspensions are dominated by the inertial effects in the suspending fluid, but these inertial interactions can be described using potential flow theory. Our main objective is to examine the effects of shear and gravity on the average properties and stability of these two suspensions.

Sangani, Ashor S.↗

NASA NTRS2000

Tar Production from Biomass Pyrolysis in a Fluidized Bed Reactor: A Novel Turbulent Multiphase Flow Formulation

A novel multiphase flow model is presented for describing the pyrolysis of biomass in a 'bubbling' fluidized bed reactor. The mixture of biomass and sand in a gaseous flow is conceptualized as a particulate phase composed of two classes interacting with the carrier gaseous flow. The solid biomass is composed of three initial species: cellulose, hemicellulose and lignin. From each of these initial species, two new solid species originate during pyrolysis: an 'active' species and a char, thus totaling seven solid-biomass species. The gas phase is composed of the original carrier gas (steam), tar and gas; the last two species originate from the volumetric pyrolysis reaction. The conservation equations are derived from the Boltzmann equations through ensemble averaging. Stresses in the gaseous phase are the sum of the Newtonian and Reynolds (turbulent) contributions. The particulate phase stresses are the sum of collisional and Reynolds contributions. Heat transfer between phases, and heat transfer between classes in the particulate phase is modeled, the last resulting from collisions between sand and biomass. Closure of the equations must be performed by modeling the Reynolds stresses for both phases. The results of a simplified version (first step) of the model are presented.

Bellan, J.↗

NASA NTRS1994

Towards a Modern Theory of Multiphase Filtration Flow

An alternative theoretical model of joint filtration flow of immiscible incompressible fluids is presented. The model takes into account relaxation processes due to the interchange of the fluids between pores of difference sizes which is driven by capillary forces. The fluids occupy connected regions in a four-dimensional space formed by three coordinates and the pore length scale. When the fluid exchange between pores of given sizes is effected by way of successive flow through pores of all the intermediate sizes, the pressure within each region is governed by a hyperbolic equation, the role of time being played by the pore linear scale. Pressure jumps across hypersurfaces separating the regions equal corresponding values of the capillary pressure. A supplementary condition at any such hypersurface requires the speed of its displacement in the four-dimensional space to coincide with the normal velocity components of both the adjoining fluids. As a result, a principally new statement of multiphase filtration flow problems is gained with allowance for capillary relaxation in the porous space.

Buyevich, Yu A.↗

NASA NTRS2002

Phase-Field Methods for Structure Evolution in Sheared Multiphase Systems

A homogeneous disordered phase separates into ordered structures when quenched into a broken-symmetry phase. The competition of broken-symmetry phases to select an equilibrium state may be studied in terms of coarse-grained order parameters described by a suitable Landau free-energy function. A network of equilibrium-phase domains develops on quenching and coarsens with time with a topology that may be controlled by shear. We use three-dimensional simulations, in which time-dependent models for conserved-order parameters coupled to Navier-Stokes fluid models are solved, to investigate the evolution of such domains, e.g. spinodal decompositions of polymeric materials under shear. The numerical problems are formidable because of the strong nonlinearities inherent in the coupled model, and these are amongst the first 3D calculations undertaken. In linear shear fields we find stable nanostrings, also recently seen in experiments. The affinity of the ordered phases to boundaries plays a role in the form of the structures that develop, with stacked plate-like phase distributions emerging under certain conditions. Such methods appear quite promising for design and analysis of multiphase and complex fluid formulations. The behavior of foams in such conditions is of particular interest in microgravity environments. Additional information can be found in the original extended abstract.

Badalassi, Vittorio↗

NASA NTRS2003

Unstructured LES of Reacting Multiphase Flows in Realistic Gas Turbine Combustors

As part of the Accelerated Strategic Computing Initiative (ASCI) program, an accurate and robust simulation tool is being developed to perform high-fidelity LES studies of multiphase, multiscale turbulent reacting flows in aircraft gas turbine combustor configurations using hybrid unstructured grids. In the combustor, pressurized gas from the upstream compressor is reacted with atomized liquid fuel to produce the combustion products that drive the downstream turbine. The Large Eddy Simulation (LES) approach is used to simulate the combustor because of its demonstrated superiority over RANS in predicting turbulent mixing, which is central to combustion. This paper summarizes the accomplishments of the combustor group over the past year, concentrating mainly on the two major milestones achieved this year: 1) Large scale simulation: A major rewrite and redesign of the flagship unstructured LES code has allowed the group to perform large eddy simulations of the complete combustor geometry (all 18 injectors) with over 100 million control volumes; 2) Multi-physics simulation in complex geometry: The first multi-physics simulations including fuel spray breakup, coalescence, evaporation, and combustion are now being performed in a single periodic sector (1/18th) of an actual Pratt & Whitney combustor geometry.

Ham, Frank↗

NASA NTRS2003

Turbulent Mixing of Multiphase Flow

Thus we conduct numerical simulations of multiphase fluids stirred by two-dimensional turbulence to assess the possibility of self-similar drop size distribution in turbulence. In our turbulence simulations, we also explore the non-diffusive limit, where molecular mobility for the interface is vanishing. Special care is needed to transport the non-diffusive interface. Numerically, we use the particle level set method to evolve the interface. Instead of using the usual methods to calculate the surface tension force from the level set function, we reconstruct the interface based on phase- field modeling, and calculate the continuum surface tension forcing from the reconstructed interface.

Young, Y.-N.↗

NASA NTRS2003

Report on Multiphase Flow Panel

This paper presents viewgraphs on a multiphase flow panel. The topics include: 1) Discussion of Priorities; 2) Critical Issues Reduced Gravity Instabilities; 3) Severely Limiting Phase Separation; 4) Severely-Limiting Phase Change; 5) Enhancements; 6) Awareness Instabilities; 7) Awareness; 8) Methods of Resolution; 9) 2008 Space Flight; 10) 2003-2008 Ground-Based Microgravity Facilities; 11) 2003-2008 Other; 12) 2009-2015 Space Flight; 13) 2009-2015 Ground-Based Microgravity Facilities; 14) 2009-2015 Other; and 15) 2016.

Source record↗