Strong and weak interactions of a V-shaped premixed swirling flame with outer vortex rings

This paper reports two distinct vortex-flame interaction mechanisms existing in a self-excited V-shaped premixed flame. Time-resolved simultaneous measurements of particle image velocimetry (PIV) and OH* chemiluminescence are employed to capture the mean and coherent flow and flame structures. The qualitative study demonstrates the importance of the outer vortex rings (OVR) in governing the flame front dynamics of two representative lean and near-stoichiometric cases. The interaction of the flame with the OVRs is further analyzed quantitatively during one OVR's entire lifespan. Results suggest that the vortex-flame interaction in the lean case is a weak one as the response of the flame's HRR to OVR's growth is interrupted by the tip extinction. This can be understood as a response to the flow perturbation excited in the Helmholtz mode of the plenum. However, the near-stoichiometric case yields a strong interaction that the peak HRR is synchronized with the OVR's peak circulation, which could contribute to a stronger thermoacoustic coupling that leads to the stronger pressure oscillation and frequency drift away from the Helmholtz mode.