ACERC
Abstracts - 1997 |
ACERC
Abstracts - 1997 |
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Thrust Area 5: Comprehensive Model Development |
Sikorski, K.
Oxford University Press, England, 1997. Funded in part by ACERC.
The purpose of this book is to provide an overview of optima computational methods for the solution of nonlinear algebraic equations, fixed points of contractive and noncontractive mappings, and for the computation of the topological degree. We analyze the worst case setting here. This means that for a given error criterion and tolerance e the methods guarantee to compute an e-approximation to the solution for every problem element in a given class F. The optimal methods solve the problem with the smallest possible cost that is called the e-complexity of the problem.
We study several classes of functions with special emphasis on tight complexity bounds and methods that are close to or achieve these bounds. In addition, pseudo codes and numerical tests of several methods are also exhibited.
Cannon, S.M.
Modeling of Lean Premixed Gaseous Turbulent Combustion, Ph.D./BYU, December
1997. Advisor: Smoot
Cannon, S.M.; Brewster,
B.S. and Smoot, L.D.
Combustion & Flame, (in press), 1997. Funded by ACERC.
The ability to use reduced CH4-air chemical mechanisms to predict CO and NO emission in premixed turbulent combustion has been evaluated in a Partially Stirred Reactor (PaSR) model. CO emissions were described with reduced 4-, 5-, and 9-step mechanisms and a detailed 276-step mechanism. NO emissions from thermal N2O-intermediate and prompt pathways were included in the 5-, 9- and 276-step mechanisms. Molecular mixing was described with a deterministic, Interaction-by-Exchange-with-the-Mean (IEM) submodel. Random selection and replacement (without repetition) of fluid particles was used to simulate through-flow. The evolution of mean and rms temperature, CO, and NO in the PaSR was accurately described with the 9-step mechanisms over a wide range in mixing frequency and equivalence ratio. Also, the 9-step mechanism provided accurate instantaneous reaction rates and concentrations for a broad region of the accessed composition space in the PaSR. The 5-step mechanism performed less reliably than the 9-step mechanism at phi = 1.0 but performed similarly to the 9-step mechanism at phi = 0.65. The 4-step mechanism underpredicted mean CO values and overpredicted instantaneous temperature reaction rates, most likely due to its inferior parent mechanism, partial equilibrium assumption for OH, and unallowed dissociation of neglected radical species. The detailed reduced mechanism predictions of the accessed composition space in the PaSR covered only a small fraction of the allowable composition space, thus facilitating the use of an efficient, in situ chemical look-up table in multi-dimensional, pdf-method calculations.
Cannon, S.M.; Brewster,
B.S.; Smoot, L.D.; Murray, R. and Hedman, P.O.
Presented at the Spring Meeting of the Western States Section/The Combustion
Institute, Sandia National Laboratories, Livermore, California, April 14-15,
1997. Funded by US Department of Energy.
The velocity composition pdf model coupled with a mean flow CFD model was used to describe the turbulent fluid flow, heat transfer, chemistry, and their interactions in a swirling, lean premixed, methane-air combustor for which laser-based measurements of mean velocity and temperature were made. A flame was stabilized in this axi-symmetric, lab-scale, gas-turbine combustor (LSGTC. A reduced, 5-step chemical mechanism, for describing fuel oxidation and NO chemistry, was used in this LSGTC model. NO emissions from thermal, N2)-intermediate, and prompt pathways were described with this 5-step mechanism. The chemistry calculations were performed efficiently with and in-situ look-up table. An axi-symmetric, unstructured grid consisting of 2283 vertices and 4302 triangular elements was used for solving the Eulerian, mean flow equations and the vertices were used to store mean statistics for solving the Lagrangian, fluid particle (~310,000 fluid particles) equations. Predicted velocity and composition statistics were compared to measurements in the LSGTC for lean equivalence ratios of 0.8 and 0.65. The comparisons of predicted mean velocity and temperature were reasonable good throughout the combustor. The location and magnitude of peak axial velocity was well represented by the model at near inlet regions, through the negative mean axial velocity in the internal recirculation zone was over-predicted. The predicted maximum mean temperature and the penetration zone of the cold unburned fluid were in reasonable agreement with the experimental data. Correct trends in CO and NO with equivalence ration were predicted with the model. The in situ tabulation method was used to represent the chemical kinetics in this axi-symmetric combustor without requiring significant CPU time and memory. The model is currently being applied to simulate 3-dimensional, gas-turbine combustor geometries and is described in a companion paper.
Meng, F.L.; Brewster, B.S.
and Smoot, L.D.
Presented at the Spring Meeting of the Western States Section/The Combustion
Institute, Sandia National Laboratories, Livermore, California, April 14-15,
1997. Funded by US Department of Energy.
A new comprehensive COmbustion Simulation MOdel for Gas Turbines (COSMO/GT) has been developed for simulating modern gas turbine combustors. The model includes the capability of simulating lean premixed combustion of methane (or natural gas) and air, and uses and unstructured-grid flow solver to accommodate geometrical complexity. In our earlier paper we extended the velocity-composition PDF approach to an unstructured grid platform for modeling two-dimensional, axisymmetric, lean premixed turbulent combustion in a lab-scale gas turbine combustor. In this paper, the extension of this PDF approach to a three-dimensional, unstructured grid is reported. The turbulence/chemistry interaction is modeled using the velocity-composition, Monte-Carlo PDF approach coupled with a five-step kinetic mechanism of methane and air for calculating CO and NO emissions. In order to increase the calculation speed of the PDF algorithm, in situ tabulation for chemical reaction and a zonal search method for locating particle positions are used. Validation of this model for and axisymmetric, lab-scale gas turbine combustor is described in a companion paper. Application of this model has been initiated by modeling lean, premixed combustion of natural gas and air in three-dimensional gas turbine combustors.
Brown, A.L.
Modeling Soot in Pulverized in Coal Flames, M.S./BYU, August 1997. Advisor:
Fletcher
Newbold, J.
Combustion Movements and Model of and Industrial, Gas-Fired, Flat-Glass Furnace,
M.S./BYU, August 1997. Advisor: Webb
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