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- Title
Direct numerical simulation of a supercritical hydrothermal flame in a turbulent jet.
- Authors
Jin, Tai; Song, Changcheng; Wang, Haiou; Gao, Zhengwei; Luo, Kun; Fan, Jianren
- Abstract
The aim of this study is to establish a fundamental understanding of the flame structure and autoignition characteristics of supercritical hydrothermal flames in three-dimensional shear-driven turbulence. The study involves direct numerical simulation of a non-premixed flame (with fuel comprising a mixture of 10 % $\textrm {H}_2$ and 90 % $\textrm {H}_2\textrm {O}$ in terms of mole fraction) at 25.0 MPa in a slot jet; detailed reaction mechanism and multispecies real-fluid properties are considered in the simulation. Qualitative transient inspection revealed that the flame undergoes a three-stage development process in the streamwise direction: sparse autoignition kernels in the upstream region, intense ignitions and establishment of a continuous flame surface in the middle region, and massive flamelets in the downstream region. Ignition kernels primarily form in the interior of large-scale shear-driven vortices featuring a low scalar dissipation rate. Probability density function (p.d.f.) analysis further confirmed that these kernels mainly form in the premixed combustion mode and on the fuel-lean side, in contrast to the authors' previous findings concerning autoignition in a two-dimensional mixing layer. Analysis of the preignition chemistry indicator (i.e. $\textrm {H}_2\textrm {O}_{2}$ radicals) revealed that although the fuel-rich condition has a shorter homogeneous autoignition delay time, it does not exhibit any remarkable preignition chemistry or intense heat release in the upstream or middle regions because of its large-scale flow structure. A volume rendering of the dimensionless Damköhler number ($Da$) reveals the distribution of autoignition spots and propagating flames. The joint p.d.f. of the mixture fraction and $Da$ reveals the transition from sparse ignition to intense ignition and, finally, to flame propagation.
- Subjects
TURBULENT jets (Fluid dynamics); FLAME; COMPUTER simulation; PROBABILITY density function; LEAN combustion; MOLE fraction; DIMENSIONLESS numbers
- Publication
Journal of Fluid Mechanics, 2021, Vol 922, p1
- ISSN
0022-1120
- Publication type
Article
- DOI
10.1017/jfm.2021.535