Multiscale analysis of turbulence-flame interaction in premixed flames

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 L ω are stretched strongly by the most extensional principal strain rate of eddies of scale 4L ω , 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 L s 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 2δ th contributes less than 10% to the total tangential strain rate for turbulence intensities, from u′/s L = 1.41 to u′/s L = 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.N.A.K.D. acknowledges the financial support of the Qualcomm European Research Studentship Fund in Technology. N. C. acknowledges the financial support of EPSRC