Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “flow”

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.

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

At least 1,693 records · Page 94
All sourcesNASA NTRSDOE OSTI
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 NTRS1992

Natural flow wing

The invention is a natural flow wing and a method for constructing the same. The method comprises contouring a three-dimensional upper surface and a three-dimensional lower surface of the natural flow wing independently of one another into a prescribed shape. Experimental data and theoretical analysis show that flow and pressure-loading over an upper surface of a wing tend to be conical about an apex of the wing, producing favorable and unfavorable regions of performance based on drag. The method reduces these unfavorable regions by shaping the upper surface such that the maximum thickness near a tip of the natural flow wing moves aft, thereby, contouring the wing to coincide more closely with the conical nature of the flow on the upper surface. Nearly constant compressive loading characterizes the flow field over a lower surface of the conventional wing. Magnitude of these compressive pressures on the lower surface depends on angle of attack and on a streamwise curvature of the lower surface of the wing and not on a cross-sectional spanwise curvature. The method, thereby, shapes the lower surface to create an area as large as possible with negative slopes. Any type of swept wing may be used to obtain the final, shaped geometry of the upper and lower surfaces of the natural flow wing.

Wood, Richard M.↗
NASA NTRS1992

Large eddy simulations and direct numerical simulations of high speed turbulent reacting flows

The basic objective of this research is to extend the capabilities of Large Eddy Simulations (LES) and Direct Numerical Simulations (DNS) for the computational analyses of high speed reacting flows. In the efforts related to LES, we were primarily involved with assessing the performance of the various modern methods based on the Probability Density Function (PDF) methods for providing closures for treating the subgrid fluctuation correlations of scalar quantities in reacting turbulent flows. In the work on DNS, we concentrated on understanding some of the relevant physics of compressible reacting flows by means of statistical analysis of the data generated by DNS of such flows. In the research conducted in the second year of this program, our efforts focused on the modeling of homogeneous compressible turbulent flows by PDF methods, and on DNS of non-equilibrium reacting high speed mixing layers. Some preliminary work is also in progress on PDF modeling of shear flows, and also on LES of such flows.

Givi, P.↗
NASA NTRS1991

General patterns of flow field growth - Aa and blocky lavas

Lava flowfields consist of one or more flows. Four ideal emplacement regimes are recognized: that for single flows and that for flowfields dominated by (1) widening, (2) thickening, or (3) lengthening, as a result of generating new flows. Most aa and blocky lavas belong to the flowfield widening or single-flow regimes. These two regimes are analyzed assuming advance is controlled by the distal core of a flow, where motion is treated as steady, uniform, and laminar. Because of low deformation rates, the distal core is also approximated to a Newtonian fluid. Widening and, possibly, lengthening are ultimately limited by crustal resistance. After a critical cooling interval, new flows are generated from the upper reaches of the flowfield. A simple relation is derived linking flowfield dimensions and underlying slope to eruption duration, independent of terms involving gravity or lava chemistry and rheology. The relation well describes field data from several volcanoes (involving lava compositions from K phonolitic tephrite to dacite). This supports the premise that the overall growth of aa and blocky flowfields is systematic and also suggests that such growth may be predictable at timescales greater than, or similar to, the emplacement times of major flows.

Kilburn, Christopher R. J.↗
NASA NTRS1992

Lava flows are fractals

Results are presented of a preliminary investigation of the fractal nature of the plan-view shapes of lava flows in Hawaii (based on field measurements and aerial photographs), as well as in Idaho and the Galapagos Islands (using aerial photographs only). The shapes of the lava flow margins are found to be fractals: lava flow shape is scale-invariant. This observation suggests that nonlinear forces are operating in them because nonlinear systems frequently produce fractals. A'a and pahoehoe flows can be distinguished by their fractal dimensions (D). The majority of the a'a flows measured have D between 1.05 and 1.09, whereas the pahoehoe flows generally have higher D (1.14-1.23). The analysis is extended to other planetary bodies by measuring flows from orbital images of Venus, Mars, and the moon. All are fractal and have D consistent with the range of terrestrial a'a and have D consistent with the range of terrestrial a'a and pahoehoe values.

Bruno, B. C.↗
NASA NTRS1991

A 2-D oscillating flow analysis in Stirling engine heat exchangers

A two-dimensional oscillating flow analysis was conducted, simulating the gas flow inside Stirling heat exchangers. Both laminar and turbulent oscillating pipe flow were investigated numerically for Re(max) = 1920 (Va = 80), 10800 (Va = 272), 19300 (Va = 272), and 60800 (Va = 126). The results are compared with experimental results of previous investigators. Also, predictions of the flow regime on present oscillating flow conditions were checked by comparing velocity amplitudes and phase differences with those from laminar theory and quasi-steady profile. A high Reynolds number k-epsilon turbulence model was used for turbulent oscillating pipe flow. Finally, performance evaluation of the K-epsilon model was made to explore the applicability of quasi-steady turbulent models to unsteady oscillating flow analysis.

Ahn, Kyung H.↗
NASA NTRS1992

Some effects of oscillation waveform and amplitude on unsteady turbulent shear flows

Some physical features of several unsteady separating turbulent boundary layers are presented for practical Reynolds numbers and reduced frequencies such as for helicopter and turbomachinery flows. The effects of unsteadiness amplitude and waveform are examined for flows along the floor of a converging and diverging wind tunnel test section. At the end of the converging portion, the mean skin friction coefficient normalized on the mean dynamic pressure is independent of the waveform and amplitude within low experimental uncertainties. In the detaching and detached portions of the flow, wall values of the fraction of time that the flow moves downstream of gamma sub pu, which is a separated flow state variable, shows that oscillation waveform and amplitude strongly influence the detached flow behavior. Distributions of gamma sub pu during a cycle indicate hysteresis within the detached flow and the effects of the higher harmonics of pressure gradient and velocity.

Agarwal, Naval K.↗
NASA NTRS1992

Coupled numerical simulation of the external and engine inlet flows for the F-18 at large incidence

This paper presents a numerical simulation of the external and engine inlet flows for the F-18 aircraft at typical high-angle-of-attack flight conditions. Two engine inlet mass flow rates, corresponding to flight idle and maximum power, were computed. This was accomplished using a structured, overset grid technique to couple the external and internal grid systems. Reynolds-averaged Navier-Stokes solutions were obtained using an implicit, finite-differencing scheme. Results show a strong coupling of the external and engine inlet flows, especially at the maximum power setting. Increasing the mass flow rate through the inlet caused the primary vortex breakdown location to move downstream. This trend is also observed in flight tests performed on the F-18. A reversed flow region upstream of the inlet duct is visible in the faired-inlet and flight-idle computations. This flow reversal is not present in the maximum power setting computation. These large-scale changes in flow structure highlight the importance of simulating inlet conditions in high-angle-of-attack aircraft computations.

Murman, Scott M.↗
NASA NTRS1993

Monolithic Continuous-Flow Bioreactors

Monolithic ceramic matrices containing many small flow passages useful as continuous-flow bioreactors. Ceramic matrix containing passages made by extruding and firing suitable ceramic. Pores in matrix provide attachment medium for film of cells and allow free movement of solution. Material one not toxic to micro-organisms grown in reactor. In reactor, liquid nutrients flow over, and liquid reaction products flow from, cell culture immobilized in one set of channels while oxygen flows to, and gaseous reaction products flow from, culture in adjacent set of passages. Cells live on inner surfaces containing flowing nutrient and in pores of walls of passages. Ready access to nutrients and oxygen in channels. They generate continuous high yield characteristic of immobilized cells, without large expenditure of energy otherwise incurred if necessary to pump nutrient solution through dense biomass as in bioreactors of other types.

Stephanopoulos, Gregory↗
NASA NTRS1992

LV software for supersonic flow analysis

The NASA Lewis Research Center (LeRC) maintains a leadership position in research into advanced aerospace propulsion systems. For the next generation of aircraft, engine designs continue to involve complex, high-speed flows. Performing the detailed flow diagnostics to properly evaluate these designs requires advanced instrumentation to probe these highly turbulent flows. The hostile flow environment often requires nonintrusive measurement techniques such as the laser velocimeter (LV). Since the LV is a proven instrument for nonintrusive flow measurement, it can provide quantitative velocity data with minimal interference to the flow. Based on anticipated flow conditions, laser velocimeter systems were procured from TSI, Inc. The initial system utilized counter processor technology, but later procurements this past year include a more advanced, correlator-based processor, which significantly improves the overall LV performance. To meet the needs of advanced research into propulsion, this instrument must be integrated into an existing VAX/VMS computer system for data acquisition, processing, and presentation. The work done under this grant before this period concentrated on developing the software required to setup and acquire data from the TSI MI-990 multichannel interface, and the RMR 1989 rotating machinery resolver. With the basis established for controlling the operation of the LV system, software development this past year shifted in emphasis from instrumentation control and data acquisition to data analysis and presentation. The progress of the program is reported.

Bell, William A.↗
NASA NTRS1992

Navier-Stokes simulations of unsteady transonic flow phenomena

Numerical simulations of two classes of unsteady flows are obtained via the Navier-Stokes equations: a blast-wave/target interaction problem class and a transonic cavity flow problem class. The method developed for the viscous blast-wave/target interaction problem assumes a laminar, perfect gas implemented in a structured finite-volume framework. The approximately factored implicit scheme uses Newton subiterations to obtain the spatially and temporally second-order accurate time history of the blast-waves with stationary targets. The inviscid flux is evaluated using either of two upwind techniques, while the full viscous terms are computed by central differencing. Comparisons of unsteady numerical, analytical, and experimental results are made in two- and three-dimensions for Couette flows, a starting shock-tunnel, and a shock-tube blockage study. The results show accurate wave speed resolution and nonoscillatory discontinuity capturing of the predominantly inviscid flows. Viscous effects were increasingly significant at large post-interaction times. While the blast-wave/target interaction problem benefits from high-resolution methods applied to the Euler terms, the transonic cavity flow problem requires the use of an efficient scheme implemented in a geometrically flexible overset mesh environment. Hence, the Reynolds averaged Navier-Stokes equations implemented in a diagonal form are applied to the cavity flow class of problems. Comparisons between numerical and experimental results are made in two-dimensions for free shear layers and both rectangular and quieted cavities, and in three-dimensions for Stratospheric Observatory For Infrared Astronomy (SOFIA) geometries. The acoustic behavior of the rectangular and three-dimensional cavity flows compare well with experiment in terms of frequency, magnitude, and quieting trends. However, there is a more rapid decrease in computed acoustic energy with frequency than observed experimentally owing to numerical dissipation. In addition, optical phase distortion due to the time-varying density field is modelled using geometrical constructs. The computed optical distortion trends compare with the experimentally inferred result, but underpredicts the fluctuating phase difference magnitude.

Atwood, C. A.↗
NASA NTRS1993

Development and verification of methods for predicting flow rates through leaks in valves and couplings

This is the final report of a research effort which addresses the title problem. The report discusses two broad models of flows, which represent the following extreme cases: (1) inertia-dominated flow, where friction is relatively insignificant; and (2) friction-dominated flow where inertia is insignificant. In class (2), the leak channel might consist of the gap between a scratch in a plastic seal and a polished metal plate against which the seal is pressed. Here, the cross section of the leak channel is modeled as a flat bottomed crescent. A publication generated under the present grant period presents an exact solution of the equations of fully-developed laminar pipe flow of a liquid in the case of a crescent beneath a hyperbolic arc. A Master's thesis project supported by the present grant presents the corresponding solution beneath a circular arc. A second publication reviews the flow of a gas through the same channel, which may be analyzed by a standard one-dimensional model (Fanno flow) for an engineering approximation. Finally, the report discusses the design and progress in the fabrication of a leak-test cell, in which one may measure the flow of fluid through a controlled flaw in a seal. The aim of such measurements is to furnish data for comparison with the predictions of the theory.

Russell, John M.↗
NASA NTRS1992

Issues and approach to develop validated analysis tools for hypersonic flows: One perspective

Critical issues concerning the modeling of low-density hypervelocity flows where thermochemical nonequilibrium effects are pronounced are discussed. Emphasis is on the development of validated analysis tools. A description of the activity in the Ames Research Center's Aerothermodynamics Branch is also given. Inherent in the process is a strong synergism between ground test and real-gas computational fluid dynamics (CFD). Approaches to develop and/or enhance phenomenological models and incorporate them into computational flow-field simulation codes are discussed. These models have been partially validated with experimental data for flows where the gas temperature is raised (compressive flows). Expanding flows, where temperatures drop, however, exhibit somewhat different behavior. Experimental data for these expanding flow conditions are sparse; reliance must be made on intuition and guidance from computational chemistry to model transport processes under these conditions. Ground-based experimental studies used to provide necessary data for model development and validation are described. Included are the performance characteristics of high-enthalpy flow facilities, such as shock tubes and ballistic ranges.

Deiwert, George S.↗
NASA NTRS1991

Three-dimensional flow calculations inside SSME GGGT first stage blade rows

A numerical analysis of the first stage of the Space Shuttle Main Engine (SSME) GGGT was conducted using a 3-D Reynolds averaged Navier-Stokes flow solver. This turbine stage was designed to improve both aerodynamic efficiency and durability. The blade has an unconventional shape with a large blade thickness. No experimental data is available to verify the computational results. The objective of the current study is to analyze this turbine blade stage with a well established Navier-Stokes computational method in order to determine if the turbine is operating in the subsonic flow regime and if these are any significant separated flow regions. The stage was analyzed in a steady state flow condition. The inlet vane was analyzed with the flow conditions from the axisymmetric entire stage solution. The viscous flow solution of the first vane is used as the inlet flow condition for the rotor.

Hah, Chunill↗
NASA NTRS1992

Magnetospheric plasma flows associated with boundary waves and flux transfer events

We describe plasma flow perturbations in the outer magnetosphere during the passage of magnetopause boundary waves and cylindrically shaped flux transfer events (FTEs). Spacecraft which remain within the magnetosphere observe bipolar flows normal to the nominal magnetopause accompanied by flows nearly opposite to the direction of boundary wave and/or FTE motion. Flows are generally discontinuous across FTE and magnetopause boundaries, with reversals in the component of flow tangential to the nominal magnetopause expected during all magnetopause crossings and some entries into FTEs. No bipolar flows normal to the nominal magnetopause occur within FTEs unless they rotate and none occur in the magnetosheath unless the boundary waves propagate relative to the magnetosheath flow. IRM satellite observations on October 28, 1984 may be interpreted either in terms of FTEs or boundary waves.

Sibeck, D. G.↗
NASA NTRS1992

Laminar flow in a recess of a hydrostatic bearing

The flow in a recess of a hydrostatic journal bearing is studied in detail. The Navier-Stokes equations for the laminar flow of an incompressible liquid are solved numerically in a two-dimensional plane of a typical bearing recess. Pressure- and shear-induced flows, as well as a combination of these two flow conditions, are analyzed. Recess friction, pressure-ram effects at discontinuities in the flow region, and film entrance pressure loss effects are calculated. Entrance pressure loss coefficients over a forward-facing step are presented as functions of the mean flow Reynolds number for pure-pressure and shear-induced laminar flows.

San Andres, Luis A.↗
NASA NTRS1992

Melt flow properties of LARC-TPI 1500 series mixtures

This study examines the melt-flow properties of 50/50 mixtures of high flow grade/medium flow grade LARC-TPI 1500 series pellets and a new form (94/6), of medium flow grade material which contains 6 percent of a low molecular weight imide additive. The flow properties are compared with previously reported flow properties of mixtures of earlier batches of high and medium flow grade TPI 1500 materials. Unlike the earlier batches of materials, the later materials were synthesized and mixed at Mitsui Toatsu Chemicals, Inc., Japan, and made into pellets before NASA received them for characterization. They exhibited a lower melt viscosity as well as improved melt stability.

Burks, H. D.↗
NASA NTRS1993

Turbulence modeling for complex hypersonic flows

The paper presents results of calculations for a range of 2D turbulent hypersonic flows using two-equation models. The baseline models and the model corrections required for good hypersonic-flow predictions will be illustrated. Three experimental data sets were chosen for comparison. They are: (1) the hypersonic flare flows of Kussoy and Horstman, (2) a 2D hypersonic compression corner flow of Coleman and Stollery, and (3) the ogive-cylinder impinging shock-expansion flows of Kussoy and Horstman. Comparisons with the experimental data have shown that baseline models under-predict the extent of flow separation but over-predict the heat transfer rate near flow reattachment. Modifications to the models are described which remove the above-mentioned deficiencies. Although we have restricted the discussion only to the selected baseline models in this paper, the modifications proposed are universal and can in principle be transferred to any existing two-equation model formulation.

Huang, P. G.↗