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At least 991 records · Page 55

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NASA NTRS2000

A Validation Summary of the NCC Turbulent Reacting/non-reacting Spray Computations

This pper provides a validation summary of the spray computations performed as a part of the NCC (National Combustion Code) development activity. NCC is being developed with the aim of advancing the current prediction tools used in the design of advanced technology combustors based on the multidimensional computational methods. The solution procedure combines the novelty of the application of the scalar Monte Carlo PDF (Probability Density Function) method to the modeling of turbulent spray flames with the ability to perform the computations on unstructured grids with parallel computing. The calculation procedure was applied to predict the flow properties of three different spray cases. One is a nonswirling unconfined reacting spray, the second is a nonswirling unconfined nonreacting spray, and the third is a confined swirl-stabilized spray flame. The comparisons involving both gas-phase and droplet velocities, droplet size distributions, and gas-phase temperatures show reasonable agreement with the available experimental data. The comparisons involve both the results obtained from the use of the Monte Carlo PDF method as well as those obtained from the conventional computational fluid dynamics (CFD) solution. Detailed comparisons in the case of a reacting nonswirling spray clearly highlight the importance of chemistry/turbulence interactions in the modeling of reacting sprays. The results from the PDF and non-PDF methods were found to be markedly different and the PDF solution is closer to the reported experimental data. The PDF computations predict that most of the combustion occurs in a predominantly diffusion-flame environment. However, the non-PDF solution predicts incorrectly that the combustion occurs in a predominantly vaporization-controlled regime. The Monte Carlo temperature distribution shows that the functional form of the PDF for the temperature fluctuations varies substantially from point to point. The results also bring to the fore some of the deficiencies associated with the use of assumed-shape PDF methods in spray computations.

Raju, M. S.↗

NASA NTRS1996

Tough, processable simultaneous semi-interpenetrating polyimides

A high temperature semi-interpenetrating polymer network (semi-IPN) was developed which had significantly improved processability, damage tolerance and mechanical performance, when compared to the commercial Thermid.RTM. materials. This simultaneous semi-IPN was prepared by mixing a thermosetting polyimide with a thermoplastic monomer precursor solution (NR-15082) and allowing them to react upon heating. This reaction occurs at a rate which decreases the flow and broadens the processing window. Upon heating at a higher temperature, there is an increase in flow. Because of the improved flow properties, broadened processing window and enhanced toughness, high strength polymer matrix composites, adhesives and molded articles can now be prepared from the acetylene endcapped polyimides which were previously inherently brittle and difficult to process.

Pater, Ruth H.↗

NASA NTRS1989

Application of two-component phase Doppler interferometry to the measurement of particle size, mass flux, and velocities in two-phase flows

Two-component phase Doppler interferometry is described, along with its application for the spatially-resolved measurements of particle size, velocity, and mass flux as well as continuous phase velocity. This technique measures single particle events at a point in the flow; droplet size is deduced from the spatial phase shift of the Doppler signal. Particle size influence and discrimination of continuous and discrete phases are among issues covered. Applications are presented for four cases: an example of the discrimination of two sizes of glass beads in a jet flow; a demonstration of the discrimination of phases in a spray field; an assessment of atomizer symmetry with respect to fuel distribution; and a characterization of a droplet field in a reacting spray. It is noted that the above technique is especially powerful in delineating droplet interactions in the swirling, complex flows typical of realistic systems.

Mcdonell, V. G.↗

NASA NTRS1991

Effect of non-equilibrium flow chemistry and surface catalysis on surface heating to AFE

The effect of nonequilibrium flow chemistry on the surface temperature distribution over the forebody heat shield on the Aeroassisted Flight Experiment (AFE) vehicle was investigated using a reacting boundary-layer code. Computations were performed by using boundary-layer-edge properties determined from global iterations between the boundary-layer code and flow field solutions from a viscous shock layer (VSL) and a full Navier-Stokes solution. Surface temperature distribution over the AFE heat shield was calculated for two flight conditions during a nominal AFE trajectory. This study indicates that the surface temperature distribution is sensitive to the nonequilibrium chemistry in the shock layer. Heating distributions over the AFE forebody calculated using nonequilibrium edge properties were similar to values calculated using the VSL program.

Stewart, David A.↗

NASA NTRS1979

Rates of the reactions of 1, 1, 1-trichloroethane /methyl chloroform/ and 1, 1, 2-trichloroethane with OH

Highly purified samples of the two chlorocarbons, trichloroethane and methyl chloroform, were reacted with OH over the temperature range of 278 to 460 K in a discharge-flow system with resonance flourescence detection of OH. Attention is given to the data obtained at various temperature levels and to the graph of Arrhenius' diagram. It is determined that the methyl chloroform reaction was slower and its temperature dependence somewhat steeper than the earlier measurements had indicated, probably due to the presence of faster reacting olefinic impurities in prior studies. Implications for stratospheric ozone reductions by C10-sub-x catalysis and for tropospheric OH-budget are briefly discussed.

Jeong, K.-M.↗

DOE OSTI2021

Scaling of oxygen-methane reacting coaxial jets using x-ray fluorescence to measure mixture fraction

Stoichiometric mixing length L s of reacting coaxial jet flames is a critical scaling parameter for liquid rocket engine combustors. Previous studies have shown that L s for shear coaxial flames can be scaled like their non-reacting counterparts using a non-dimensional momentum flux ratio J. In addition, stoichiometric mixing lengths of reacting and nonreacting coaxial jets collapse upon a single line by altering J using an effective outer flow gas density. This effective density is calculated from a modified version of the equivalence principle, originally developed by Tacina and Dahm [1, 2] and accounts for the effects of heat release on mixing. However, previous studies also required a second nonphysical scaling constant S c for the reacting jets, which is not predicted by the equivalence principle [3]. It was originally hypothesized that S c is attributed to the limitation of hydroxyl (OH) planar laser-induced fluorescence, which only infers L s . Direct quantitative measurement of conserved scalar fields using conventional optical diagnostics is difficult due to the lack of a tracer that easily fluoresces, survives high temperature oxygen flames, and is not dominated by quenching effects. To measure a conserved scalar field, this work implements x-ray fluorescence of Kr and Ar tracers to obtain quantitative mixture fraction fields. From these mixture fraction fields, stoichiometric mixing lengths for two CH 4 /O 2 flames are calculated and scaled against nonreacting coaxial mixing lengths using the equivalence principle. By directly measuring the stoichiometric mixing length, it is established that the additional constant is a byproduct of the OH measurement technique and the equivalence principle fully captures the scaling. Finally, comparison with high-fidelity simulation of the flame further supports this conclusion. In addition to further strengthening this scaling method, this work represents the first use of x-ray fluorescence to make quantitative conserved scalar measurements in turbulent flames.

33 ADVANCED PROPULSION SYSTEMS↗

NASA NTRS2001

Characterization of a Laminate Flat Plate Diffusion Flame in Microgravity using PIV, Visible and CH Emissions

Motivated by fire safety concerns and the advent of long-term micro-gravity facilities, a cooperative program has been developed to study the mechanisms and material properties that control flow assisted (co-current) flame spread. This program has used as a common fire scenario a reacting steady-state boundary layer. Preliminary studies explored the aerodynamics of a reacting boundary layer by simulating a condensed fuel by means of a gas burner. Stability curves for ethane air flames were obtained and different burning regimes were identified. An important feature of this study was the independent identification of the different mechanisms leading to the instability of the flow. It was observed that fuel injection velocity and thermal expansion independently contributed to the separation of the flow at the leading edge of the burner. The occurrence of separation resulted in complex three-dimensional flow patterns that have a dominant effect on critical fire safety parameters such as the stand-off distance and flame length. This work was extended to a solid fuel (PMMA) leading to a Sounding Rocket experiment (Mini-Texus-6). The solid phase showed similar flow patterns, mostly present at low flow velocities (<100 mm/s) but the results clearly demonstrated that the thermal balance at the pyrolyzing fuel surface is the dominant mechanism that controls both stand-off distance and flame length. This thermal balance could be described in a global manner by means of a total mass transfer or "B" number. This "B" number incorporates surface re-radiation, radiative feedback and in-depth heat conduction as first prescribed by Emmons. The mass transfer number becomes the single parameter that determines the evolution of these fire safety variables (flame length, stand-off distance) and therefore can be used as a ranking criterion to assess the flammability of materials. The particular configuration is representative of the NASA upward flame spread test (Test 1) therefore this approach can be used in the interpretation of the results obtained from this test. Nevertheless, complete validation of this approach has not been fully achieved due, mainly because all the measurements necessary to compare with the theoretical predictions have not been obtained. Following these studies two different directions have been taken. The first attempts to elucidate the details of the gas phase combustion reaction and the associated flow field by means of quantitative and qualitative measurements. The second approach, a more practical one, is to apply this methodology to the assessment of material flammability. The former is currently being conducted with a gas burner because it allows for easier control and longer experimentation time. The results obtained so far will be presented in more detail. The latter is a new program therefore only a brief summary of the objectives will be presented.

Joulain, P.↗

NASA NTRS1976

Two techniques for eliminating luminol interference material and flow system configurations for luminol and firefly luciferase systems

Two methods for eliminating luminol interference materials are described. One method eliminates interference from organic material by pre-reacting a sample with dilute hydrogen peroxide. The reaction rate resolution method for eliminating inorganic forms of interference is also described. The combination of the two methods makes the luminol system more specific for bacteria. Flow system designs for both the firefly luciferase and luminol bacteria detection systems are described. The firefly luciferase flow system incorporating nitric acid extraction and optimal dilutions has a functional sensitivity of 3 x 100,000 E. coli/ml. The luminol flow system incorporates the hydrogen peroxide pretreatment and the reaction rate resolution techniques for eliminating interference. The functional sensitivity of the luminol flow system is 1 x 10,000 E. coli/ml.

Thomas, R. R.↗

DOE OSTI2022

Multiscale Interaction of Turbulence, Temperature, and Soot Formation: Measurements for Critical Assessments of Chemical Kinetics and Mechanisms

This program targeted an improved understanding of how turbulence affects soot formation chemistry (directly and indirectly) with a particular focus on detailing the multiscale coupling between flow turbulence, mixing, thermal transport, and soot formation kinetics in gas-phase reacting systems. In this project, simultaneous, quantitative multi-dimensional velocity, soot volume fraction, and gas-phase temperature measurements in turbulent non-premixed sooting flames were developed. These new diagnostics tools can be used to elucidate the relative effects of fluid kinematics, mixing, thermal processes, and turbulence/scalar time/length scales on soot formation chemistry and topology. Simultaneous multi-parameter measurements were acquired within a series of flames with different Reynolds numbers and spatial locations to investigate the inter-dependence of soot, temperature, and turbulence within the soot inception, growth, and oxidation region. Preliminary assessment of the results has been completed at the project end and detailed analysis is planned following the completed program.

02 PETROLEUM↗

NASA NTRS1994

Tough, processable semi-interpenetrating polymer networks from monomer reactants

A high temperature semi-interpenetrating polymer network (semi-IPN) was developed which had significantly improved processability, damage tolerance, and mechanical performance, when compared to the commercial Thermid materials. This simultaneous semi-IPN was prepared by mixing the monomer precursors of Thermid AL-600 (a thermoset) and NR-150B2 (a thermoplastic) and allowing the monomers to react randomly upon heating. This reaction occurs at a rate which decreases the flow and broadens the processing window. Upon heating at a higher temperature, there is an increase in flow. Because of the improved flow properties, broadened processing window and enhanced toughness, high strength polymer matrix composites, adhesives and molded articles can now be prepared from the acetylene end-capped polyimides which were previously inherently brittle and difficult to process.

Pater, Ruth H.↗

NASA NTRS2009

Wind-US Code Physical Modeling Improvements to Complement Hypersonic Testing and Evaluation

This report gives an overview of physical modeling enhancements to the Wind-US flow solver which were made to improve the capabilities for simulation of hypersonic flows and the reliability of computations to complement hypersonic testing. The improvements include advanced turbulence models, a bypass transition model, a conjugate (or closely coupled to vehicle structure) conduction-convection heat transfer capability, and an upgraded high-speed combustion solver. A Mach 5 shock-wave boundary layer interaction problem is used to investigate the benefits of k- s and k-w based explicit algebraic stress turbulence models relative to linear two-equation models. The bypass transition model is validated using data from experiments for incompressible boundary layers and a Mach 7.9 cone flow. The conjugate heat transfer method is validated for a test case involving reacting H2-O2 rocket exhaust over cooled calorimeter panels. A dual-mode scramjet configuration is investigated using both a simplified 1-step kinetics mechanism and an 8-step mechanism. Additionally, variations in the turbulent Prandtl and Schmidt numbers are considered for this scramjet configuration.

Georgiadis, Nicholas J.↗

NASA NTRS1995

Computational study of inlet injection for a Pre-Mixed, Shock-Induced Combustion (PM/SIC) engine

A computational simulation of reacting 2-D and 3-D flowfields in a model inlet section of a Pre-Mixed, Shock-Induced Combustion (PM/SIC) engine concept was performed. LARCK, a multi-dimensional Navier-Stokes code with finite-rate kinetics chemistry developed at NASA LaRC by J.A. White, was adapted for this simulation. The flow conditions in the simulation match those envisioned for the PM/SIC engine experiments currently planned at LaRC. The reacting flowfields were Mach 6.3 freestream air and Mach 2 hydrogen at various pressure and temperature conditions injected through a slot injector at the base of the inlet section. In the PM/SIC engine, fuel is injected at the inlet section upstream of the combustor, and reaction is initiated by the shock wave at the inlet which increases the gas temperature and pressure beyond the kinetic limits for reaction. Many challenges exist prior to establishing shock-controlled combustion as a practical engine concept. These challenges include fuel injection schemes that can provide proper fuel-air mixing without creating large losses in the inlet section, and control of the combustion process so that early ignition or combustion propagation through the inlet boundary layer does not occur. For this project, a parametrics study was carried out to model the fuel injection of hydrogen at different flow conditions. It was found that, as the fuel temperature and pressure were increased, the potential for pre-ignition was high at a short distance downstream of the slot injector. The next stage of this work will investigate injection techniques for enhancing mixing of fuel and air in a manner that prevents or reduces the potential for premature ignition observed numerically.

Gonzalez, D. E.↗

NASA NTRS1986

A detailed numerical model of a supersonic reacting mixing layer

A current research effort is underway at the NASA Langley Research Center to achieve a detailed understanding of important phenomena present when a supersonic flow undergoes chemical reaction. A computer program has been developed to study the details of such flows. The program has been constructed to consider the multicomponent diffusion and convection of important species, the finite-rate reaction of these species, and the resulting interaction between the fluid mechanics and chemistry. Code results from the analysis of a spatially developing and reacting mixing layer are presented, and conclusions are drawn regarding the structure of the evolving layer and its associated flame.

Drummond, J. P.↗

NASA NTRS1987

A numerical model for supersonic reacting mixing layers

A current research effort is underway at the NASA Langley Research Center to achieve a detailed understanding of important phenomena present when a supersonic flow undergoes a chemical reaction. A computer program has been developed to study the details of such flows. The program has been constructed to consider the multicomponent diffusion and convection of important species, the finite-rate reaction of these species, and the resulting interaction between the fluid mechanics and chemistry. Code results from the analysis of a spatially developing and reacting mixing layer are presented, and conclusions are drawn regarding the structure of the evolving layer and its associated flame.

Drummond, J. Philip↗

NASA NTRS1988

Numerical solutions of the complete Navier-Stokes equations

The physical phenomena within supersonic flows that sustain chemical reactions are investigated. An earlier study to develop accurate physical models for supersonic reacting flowfields focused on 2-D laminar shear layers. The objective is to examine the mixing and subsequent combustion within turbulent reacting shear layers. To conduct this study, a computer program has been written to solve the axisymmetric Reynolds averaged Navier-Stokes equations. The numerical method uses a cell-centered finite volume approach and a Runge Kutta time stepping scheme. The Reynolds averaged equations are closed using the eddy viscosity concept. Several zero-equation models have been tested by making calculations for an H2-air nonreacting coaxial jet flow. Comparisons made with experimental data show that Cohen's eddy viscosity model provides best agreement. The finite rate chemistry model used in the study of 2-D laminar shear layers is incorporated into the computer program and data is compared from a recent experiment performed at NASA Langley.

Hassan, H. A.↗

DOE OSTI2023

Evaluation of the interaction between SiC, pre-oxidized FeCrAlMo with aluminized and pre-oxidized Fe-8Cr-2W in flowing PbLi

We report dissimilar materials interactions are a major concern when liquid metals are used as a working fluid. To simulate a dual-coolant PbLi blanket, chemical vapor deposited (CVD) SiC, pre-oxidized FeCrAlMo (APMT) and pre-oxidized aluminized coating on Fe-8Cr-2 W (F82H) specimens were exposed to flowing commercial Pb-17at.%Li with a peak temperature of 650 °C in a pre-oxidized APMT thermal convection loop (TCL) for 1000 h. Similar to prior results in static PbLi, the coated F82H showed small mass changes and limited degradation of room-temperature tensile properties. After exposure, the α-Al 2 O 3 on the surface coated F82H reacted with the PbLi to form LiAlO 2 . However, no significant Al coating loss or interdiffusion was observed. Mass transfer was observed between the APMT, TCL and the SiC specimens. Fe, Cr and Ni were dissolved into the molten flowing PbLi and transported through the TCL to react with the SiC specimens. Compared to a prior experiment with a majority of bare FeCrAl specimens that were exposed in a TCL with a peak temperature of 700 °C for 1000 h, the SiC reaction was reduced to only a few microns of carbides and silicides. Oxygen dissolved in the molten PbLi sustained the formation of an Al 2 O 3 scale on the surface of the coating and induced the formation of a thin surface SiO 2 layer on the surface of the SiC.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Flow Measurements in Pressurized Helium Gas Cooling Channels: Rev. 1

Compressed helium gas is used to cool the NorthStar Medical Radioisotope (NMR) target system, also called the trident, chosen due to its superior heat transfer capabilities and its inability to react with Molybdenum-100 (Mo-100) during irradiation. To test the housing and NMR target stack at Los Alamos National Laboratory (LANL), two sets of helium gas flow loop facilities have been set-up and tested. One system is used for bench-top experiments to systematically investigate individual components of the NMR target, and the other, larger system is more representative of the system at NMR and is used for testing the full NMR target stack.

43 PARTICLE ACCELERATORS↗

NASA NTRS1973

A theoretical and experimental study of sound attenuation in an annular duct.

The flow duct used in the experiments for this study was described in an earlier paper by Plumblee and Dean (1972). Angular and radial standing modes were excited in isolation, and the modal attenuation and phase speed were measured in an annular duct with locally reacting liners. Contour maps of constant attenuation and phase speed were computed in the wall impedance plane for no-flow and several flow conditions, and experimental data were compared with some of these calculations. The effect of flow on modal attenuation and phase speed was measured and is theoretically verified. The major result of this study is the verification of theoretical predictions which ultimately can lead to a duct liner design optimization without resort to expensive and lengthy test programs.

Plumblee, H. E.↗