Complex network analysis of a premixed swirling flame influenced by precessing vortex core

This work investigates the influences of precessing vortex cores (PVCs) on the coherent interactions in the transient flow and heat release fields of a weak premixed swirling flame, based on a 10-kHz simultaneous measurement of OH^* chemiluminescence and stereoscopic particle image velocimetry together with the state-of-the-art vortical and heat release rate (HRR) network analyses. The PVC effect is studied by contrasting the lifted helical and attached symmetric states of a unique transitioning V-shaped flame, corresponding to an alternate quasi-periodic appearance and disappearance of PVC in the inner shear layer (ISL). The results suggest that the emergence of PVC significantly escalates the coherent oscillation in the ISL, leading to the break of the scale-free topology in the vortical network. However, the PVC also promotes coherence in the local HRR variation, resulting in improved connectivity in the positive HRR network and enhanced assortative mixing in the negative HRR network. Furthermore, the flame mode transition is also captured by the differences in the mean degree of the positive HRR network and the power-law fitting goodness of the negative HRR network, showing promises of complex network analysis in distinguishing the flame dynamical modes.