8,168 research outputs found
Radiation/convection coupling in rocket motor and plume analysis
A method for describing radiation/convection coupling to a flow field analysis was developed for rocket motors and plumes. The three commonly used propellant systems (H2/O2, RP-1/O2, and solid propellants) radiate primarily as: molecular emitters, non-scattering small particles (soot), and scattering larger particles (Al2O3), respectively. For the required solution, the divergence of the radiation heat flux was included in the energy equation, and the local, volume averaged intensity was determined by a solution to the radiative transfer equation. A rigorous solution to this problem is intractable, therefore, solution methods which use the ordinary and improved differential approximation were developed. This radiation model was being incorporated into the FDNS code, a Navier-Stokes flowfield solver for multiphase, turbulent combusting flows
Adaptation of multidimensional group particle tracking and particle wall-boundary condition model to the FDNS code
A particulate two-phase flow CFD model was developed based on the FDNS code which is a pressure based predictor plus multi-corrector Navier-Stokes flow solver. Turbulence models with compressibility correction and the wall function models were employed as submodels. A finite-rate chemistry model was used for reacting flow simulation. For particulate two-phase flow simulations, a Eulerian-Lagrangian solution method using an efficient implicit particle trajectory integration scheme was developed in this study. Effects of particle-gas reaction and particle size change to agglomeration or fragmentation were not considered in this investigation. At the onset of the present study, a two-dimensional version of FDNS which had been modified to treat Lagrangian tracking of particles (FDNS-2DEL) had already been written and was operational. The FDNS-2DEL code was too slow for practical use, mainly because it had not been written in a form amenable to vectorization on the Cray, nor was the full three-dimensional form of FDNS utilized. The specific objective of this study was to reorder to calculations into long single arrays for automatic vectorization on the Cray and to implement the full three-dimensional version of FDNS to produce the FDNS-3DEL code. Since the FDNS-2DEL code was slow, a very limited number of test cases had been run with it. This study was also intended to increase the number of cases simulated to verify and improve, as necessary, the particle tracking methodology coded in FDNS
Computational analysis of the SSME fuel preburner flow
A computational fluid dynamics model which simulates the steady state operation of the SSME fuel preburner is developed. Specifically, the model will be used to quantify the flow factors which cause local hot spots in the fuel preburner in order to recommend experiments whereby the control of undesirable flow features can be demonstrated. The results of a two year effort to model the preburner are presented. In this effort, investigating the fuel preburner flowfield, the appropriate transport equations were numerically solved for both an axisymmetric and a three-dimensional configuration. Continuum's VAST (Variational Solution of the Transport equations) code, in conjunction with the CM-1000 Engineering Analysis Workstation and the NASA/Ames CYBER 205, was used to perform the required calculations. It is concluded that the preburner operational anomalies are not due to steady state phenomena and must, therefore, be related to transient operational procedures
Simulation of solidification in a Bridgman cell
Bridgman-type crystal growth techniques are attractive methods for producing homogeneous, high-quality infrared detector and junction device materials. However, crystal imperfections and interface shapes still must be controlled through modification of the temperature and concentration gradients created during solidification. The objective of this investigation was to study the temperature fields generated by various cell and heatpipe configurations and operating conditions. Continuum's numerical model of the temperature, species concentrations, and velocity fields was used to describe the thermal characteristics of Bridgman cell operation
Calculation of flow about posts and powerhead model
A three dimensional analysis of the non-uniform flow around the liquid oxygen (LOX) posts in the Space Shuttle Main Engine (SSME) powerhead was performed to determine possible factors contributing to the failure of the posts. Also performed was three dimensional numerical fluid flow analysis of the high pressure fuel turbopump (HPFTP) exhaust system, consisting of the turnaround duct (TAD), two-duct hot gas manifold (HGM), and the Version B transfer ducts. The analysis was conducted in the following manner: (1) modeling the flow around a single and small clusters (2 to 10) of posts; (2) modeling the velocity field in the cross plane; and (3) modeling the entire flow region with a three dimensional network type model. Shear stress functions which will permit viscous analysis without requiring excessive numbers of computational grid points were developed. These wall functions, laminar and turbulent, have been compared to standard Blasius solutions and are directly applicable to the cylinder in cross flow class of problems to which the LOX post problem belongs
Theory of zone radiometry
A spectroscopic instrumentation system was developed which was used to measure temperature and concentration distributions in axisymmetric and two dimensional combusting flows. This measurement technique is known as zone radiometry
On Carbon Burning in Super Asymptotic Giant Branch Stars
We explore the detailed and broad properties of carbon burning in Super
Asymptotic Giant Branch (SAGB) stars with 2755 MESA stellar evolution models.
The location of first carbon ignition, quenching location of the carbon burning
flames and flashes, angular frequency of the carbon core, and carbon core mass
are studied as a function of the ZAMS mass, initial rotation rate, and mixing
parameters such as convective overshoot, semiconvection, thermohaline and
angular momentum transport. In general terms, we find these properties of
carbon burning in SAGB models are not a strong function of the initial rotation
profile, but are a sensitive function of the overshoot parameter. We
quasi-analytically derive an approximate ignition density, g cm, to predict the location of first carbon ignition
in models that ignite carbon off-center. We also find that overshoot moves the
ZAMS mass boundaries where off-center carbon ignition occurs at a nearly
uniform rate of / 1.6
. For zero overshoot, =0.0, our models in the ZAMS mass
range 8.9 to 11 show off-center carbon ignition. For
canonical amounts of overshooting, =0.016, the off-center carbon
ignition range shifts to 7.2 to 8.8 . Only systems with
and ZAMS mass 7.2-8.0 show
carbon burning is quenched a significant distance from the center. These
results suggest a careful assessment of overshoot modeling approximations on
claims that carbon burning quenches an appreciable distance from the center of
the carbon core.Comment: Accepted ApJ; 23 pages, 21 figures, 5 table
Properties of Carbon-Oxygen White Dwarfs From Monte Carlo Stellar Models
We investigate properties of carbon-oxygen white dwarfs with respect to the
composite uncertainties in the reaction rates using the stellar evolution
toolkit, Modules for Experiments in Stellar Astrophysics (MESA) and the
probability density functions in the reaction rate library STARLIB. These are
the first Monte Carlo stellar evolution studies that use complete stellar
models. Focusing on 3 M models evolved from the pre main-sequence to
the first thermal pulse, we survey the remnant core mass, composition, and
structure properties as a function of 26 STARLIB reaction rates covering
hydrogen and helium burning using a Principal Component Analysis and Spearman
Rank-Order Correlation. Relative to the arithmetic mean value, we find the
width of the 95\% confidence interval to be
0.019 M for the core mass at the first thermal pulse,
12.50 Myr for the age, 0.013 for the central temperature, 0.060 for the central density,
2.610 for the central electron
fraction, 5.810,
0.392, and 0.392. Uncertainties in the experimental
C(, triple-, and
N( reaction rates dominate these variations. We
also consider a grid of 1 to 6 M models evolved from the pre
main-sequence to the final white dwarf to probe the sensitivity of the
initial-final mass relation to experimental uncertainties in the hydrogen and
helium reaction rates.Comment: Accepted for publication in The Astrophysical Journal; 19 Pages, 23
Figures, 5 Table
Development of a three-dimensional time-dependent flow field model
A three-dimensional, time-dependent mathematical model to represent Mobile Bay was developed. Computer programs were developed which numerically solve the appropriate conservation equations for predicting bay and estuary flow fields. The model is useful for analyzing the dispersion of sea water into fresh water and the transport of sediment, and for relating field and physical model data
The changing nature of the Pb-206/Pb-207 isotopic ratio of lead in rainwater, atmospheric particulates, pine needles and leaded petrol in Scotland, 1982-1998
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