Modeling study on turbulent flows with and without combustion
| Autor: | Ching-Shun Chen, 陳慶順 |
|---|---|
| Rok vydání: | 1993 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 81 This study is to investigate the moment closures which are applied to the simulations of turbulent flows with and without combustion. The objectives of this study are: (i) to scrutinize the performanceof the investigated moment closures, (ii) to develop the modified versions of these investigated moment closures, (iii) to find out more robust treatments of I.B.C. and β-pdf in the numerical simulations of the investigated flows, and (iv) to develop a reduced kinetic mechanism for H_2- air reacting flows associated with the present moment closures. Numerical studies of confined sudden-expansion pipe flows with and without swirling reveal that all investigated κ-ε turbulence models cannot perform the satisfactory predictions as comparing to the experimental data. By taking into account the anisotropic effects to the standard κ-ε model, based upon a concept that the model constant should be modified only in the flow regions where the anisotropic effects are significant, two hybrid versions of the κ-ε model are then developed for the aforementioned flows. The encouraging improvements of predictions by using the proposed hybridκ-εmodels are obtained. This study also examines the influences of inlet boundary conditions on the computation of simultaneous momentum and scalar transports. It is proved that the predictions using the assumed inlet boundary conditions in the usual manner yield significant errors in the near inlet region, particularly for mass transport. In theoretical analysis of turbulent flame by the moment closures method, the β-pdf, which is usually employed to account for the turbulence-combustion interaction, has some singular problems occurring at the end points of the integral under some conditions which has not been subject to extensive investigation before. This study proposes a robust β- pdf treatment which can overcome all unrealistic calculations in turbulent flame simulation. Numerical simulations associated with the detailed kinetic |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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