Multiscale analysis of turbulence-flame interaction in premixed flames

N.A.K Doan,N Swaminathan,N Chakraborty

doi:10.1016/j.proci.2016.07.111

N.A.K Doan, N Swaminathan + Show 1 more

Open Access

https://doi.org/10.1016/j.proci.2016.07.111

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Abstract

Multiscale analysis of turbulence–flame interaction is performed using direct numerical simulation (DNS) data of premixed flames. Bandpass filtering method is used to educe turbulent eddies of various sizes and their vorticity and strain rate fields. The vortical structures at a scale of Lω are stretched strongly by the most extensional principal strain rate of eddies of scale 4Lω, which is similar to the behaviour in non-reacting turbulence. Hence, combustion does not influence the physics of vortex stretching mechanism. The fractional contribution from eddies of size Ls to the total tangential strain rate is investigated. The results highlight that eddies larger than two times the laminar flame thermal thickness contributes predominantly to flame straining and eddies smaller than 2δth contributes less than 10% to the total tangential strain rate for turbulence intensities, from u′/sL=1.41 to u′/sL=11.25, investigated here. The cutoff scale identified through this analysis is larger than the previous propositions and the implication of this finding to subgrid scale premixed combustion modelling is discussed.

Highlights

Most of practical combustion occurs in turbulent flows involving a strong nonlinear coupling between turbulence and chemical processes, and the flame is wrinkled and strained by turbulent eddies [1,2,3,4]
The aim of this study is to find answers to these questions by analysing Direct Numerical Simulation (DNS) data of premixed flames using a multiscale analysis called bandpass filtering technique
It is observed that vortical structures of scale Lω are stretched by larger eddies with the maximum stretching from eddies of scale about 4Lω

Summary

Introduction

Most of practical combustion occurs in turbulent flows involving a strong nonlinear coupling between turbulence and chemical processes, and the flame is wrinkled and strained by turbulent eddies [1,2,3,4]. One can query if the whole spectrum of these scales imparts influences on the flame physics or only a certain part of this spectrum influences the flame predominantly. This classical question has been raised in many earlier studies and it has been suggested that the Gibson scale may be an appropriate cutoff scale [1], and Kolmogorov scale are too weak to wrinkle or strain the flame [7,8]. Our interest here is from the perspective of combustion modelling for large eddy simulation (LES)

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