Direct Numerical Simulations of an Unpremixed Turbulent Jet Flame

摘要

Direct numerical simulations (DNS) have been performed to study the phenomenon of mixing and its effects on chemical reactions in an unpremixed turbulent reactive flow. The type of flows considered were 1) two-dimensional temporally developing mixing layers, 2) two- and three-dimensional spatially evolving mixing layers, and 3) three-dimensional homogeneous turbulent flows. The emphasis of the simulations for the first two types of flows was the local flame extinction caused by the high rate of strain in a chemically nonequilibrium turbulent flow. It was shown that flame extinction occurs in the high strain region of the braids of the coherent structures. Preliminary investigation of the three-dimensional flow shows a highly contorted flame sheet caused by the combination of the two-dimensional coherent structures and the longitudinal (streamwise) vortices. The homogeneous turbulence simulations were performed to test Toor's hypothesis. The results of the simulations suggested a revision to the hypothesis. During the course of the research, a three-dimensional spectral-element code was developed for the three-dimensional flows. The code combined the accuracy of a pseudospectral code with the flexibility of a finite element code. Scalar transport equations are included for simulations of mixing and chemical reaction in a complex three-dimensional turbulent flow. Keywords: Combustion. (AW)