Grid resolution requirement of chemical explosive mode analysis for large eddy simulations of premixed turbulent combustion

Abstract

The grid resolution requirement for trustworthy Chemical Explosive Mode Analysis (CEMA) in Large Eddy Simulation (LES) of premixed turbulent combustion is proposed. Explicit filtering, to emulate the effect of the LES filter, is applied to one-dimensional laminar flame and three-dimensional planar turbulent flames across a wide range of Karlovitz numbers $(5-239)$. The identification of the flame front by CEMA is found relatively insensitive to the cell size (Δ), while the combustion mode identification shows more significant sensitivity. Specifically, increasing Δ falsely enhances the auto-ignition and local extinction modes and suppresses the diffusion-assisted mode. Limited dependence of the CEMA performance on the turbulent combustion regime (Karlovitz number) is observed. A simple grid size criterion for reliable CEMA mode identification in LES is proposed as $\mathrm{\Delta }\lesssim {\delta }_L/2$; The criterion can be relaxed to $\mathrm{\Delta }\lesssim {\delta }_L$ in the laminar flame limit. Furthermore, theoretical analysis is conducted on an idealised chemistry-diffusion system. The effects of the filtering process and turbulence on the local combustion mode are demonstrated, which is consistent with the numerical observations. By incorporating turbulent combustion models in CEMA, potential improvement in identifying local combustion modes can be expected.

Keywords:

• chemical explosive mode analysis (CEMA)
• large eddy simulation (LES)
• premixed turbulent combustion

Acknowledgments

The numerical computations were performed using π-2.0 at the Center for High-Performance Computing, Shanghai Jiao Tong University.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The authors gratefully acknowledge financial support from the National Natural Science Foundation of China (No. 91941301 and No. 12002210) and the Shanghai Municipal Natural Science Foundation (No. 21ZR1434000). Argonne National Laboratory's work was supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy under contract DE-AC02-06CH11357.