Shear-layer effects on the dynamics of unsteady premixed laminar counterflow flames

TL;DR

This study investigates how shear-layer effects influence the behavior of unsteady premixed laminar counterflow flames, revealing that off-center locations exhibit complex dynamics dominated by higher harmonic responses linked to vortex activity.

Contribution

It extends previous research by experimentally analyzing off-center flame behavior, highlighting multi-dimensional effects and the role of vortex dynamics in unsteady counterflow flames.

Findings

Off-center flame dynamics differ significantly from centerline behavior.

Higher harmonic responses dominate off-center regions.

Vortex intensity correlates with higher harmonic strength.

Abstract

The influence of flow non-uniformity and unsteadiness on premixed flames is of considerable interest due to its direct relevance to practical combustion systems. The steady counterflow flame has long served as a canonical configuration for investigating flame dynamics under controlled, spatially non-uniform conditions. A commonly studied variation, referred to as the unsteady counterflow, introduces a controlled temporal perturbation to the otherwise steady flow from the nozzles, thereby enabling the systematic examination of the coupled effects of unsteadiness and non-uniformity. Prior investigations have focused on flame dynamics along the line of symmetry, where the reduced dimensionality of the problem facilitates analysis. In the present study, we extend this perspective by experimentally examining flame behavior at off-center locations, where multi-dimensional effects of non-uniformity and unsteadiness are more pronounced. Results reveal markedly different dynamics away from the centerline, characterized by a dominant contribution from higher harmonic responses. Further analysis of the associated vortex dynamics in the shear layer demonstrates that the intensity of these vortical structures directly governs the strength of the observed higher harmonics, and thereby the altered flame behavior.