Abstract
The turbulent counter-flow flame (TCF) has proven to be a useful benchmark to study turbulence-chemistry interactions, however, the widely observed bulk flow fluctuations and their influence on the flame stability remain unclear. In the present work, premixed TCFs are studied numerically using a Large Eddy Simulation (LES) method. A transported probability density function (pdf) approach is adopted to simulate the sub-grid scale (sgs) turbulence-chemistry interactions. A solution to the joint sgs-pdf evolution equation for each of the relative scalars is obtained by the stochastic fields method. The chemistry is represented using a simplified chemical reaction mechanism containing 15 reaction steps and 19 species. This work compares results with two meshing strategies, with the domain inside nozzles included and excluded respectively. A conditional statistical approach is applied to filter out the large scale motions of the flame. With the use of digital turbulence, the velocity field in the flame region is well reproduced. The processes of local extinction and re-ignition are successfully captured and analysed together with the strain rate field, and local extinctions are found correlated to the turbulent structures in the reactant stream. The predicted probability of localised extinction is in good agreement with the measurements, and the influence of flame stoichiometry are also successfully reproduced. Overall, the current results serve to demonstrate the capability of the LES-pdf method in the study of the premixed opposed jet turbulent flames.
Highlights
Turbulent flames involve complex mutual interactions between unsteady flows and chemical reactions over a variety of temporal and spatial scales, which poses a great challenge for combustion research
Coppola and his colleagues first studied this instability in an isothermal turbulent counter-flow flame (TCF) using proper orthogonal decomposition (POD) (Coppola and Gomez 2010; Gomez 2011), which shows the existence of two modes of the oscillation of the mixing layer, namely an axial one and a precession one about the system axis
To understand the effects of flame stoichiometry on the local extinction, we study the flame with reactant equivalence ratio varied from t = 0.5 to t = 1.0, while other flow conditions remain the same as the standard conditions
Summary
Turbulent flames involve complex mutual interactions between unsteady flows and chemical reactions over a variety of temporal and spatial scales, which poses a great challenge for combustion research. Numerical simulations can provide researchers with further. Turbulence and Combustion (2021) 106:1379–1398 understanding of the turbulence-chemistry interactions, as they have the abilities to overcome the difficulties associated with measurement techniques
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