Multifractal analysis of flame dynamics during transition to thermoacoustic instability in a turbulent combustor

Suppression of thermoacoustic instability by targeting the hubs of the turbulent networks in a bluff body stabilized combustor

“…They illustrated that the large-scale vortices observed during the periodic epoch of intermittency and thermoacoustic instability are a result of the phenomenon of collective interaction of small-scale vortices (Ho & Nosseir 1981). Recently, from the Mie-scattering images obtained from the same experimental set-up used in the present study, Raghunathan et al (2020) classified the size of the vortices as small-scale, (≈0.08 times the step size), medium-scale (≈0.24 times the step size) and large-scale (≈0.6 times the step size) during combustion noise, intermittency and thermoacoustic instability, respectively.…”

“…Recently, from the Mie-scattering images obtained from the same experimental set-up used in the present study, Raghunathan et al. (2020) classified the size of the vortices as small-scale, ( times the step size), medium-scale ( times the step size) and large-scale ( times the step size) during combustion noise, intermittency and thermoacoustic instability, respectively.…”

Seeds of phase transition to thermoacoustic instability

“…It was recently discovered that S C , referred to as combustion noise, is chaotic 41,42 . S C is also characterized by disorganized flow and flame dynamics 41,[43][44][45] . During S IN , bursts of periodic oscillations appear amidst epochs of aperiodic dynamics at apparently random intervals 39 .…”

“…During S IN , bursts of periodic oscillations appear amidst epochs of aperiodic dynamics at apparently random intervals 39 . Additionally, during S IN , macroscopic patterns at the size of the system geometry emerge during the regime of periodic oscillations, while disordered small-scale structures exist during the regime of aperiodic oscillations [43][44][45] . On the other hand, S TI typically exhibits the coexistence of large-scale coherent flow structures or vortices, spatially and temporally organized reaction fields, distinct standing wave modes, large-amplitude periodic acoustic pressure oscillations etc 44 .…”

“…On the other hand, S TI typically exhibits the coexistence of large-scale coherent flow structures or vortices, spatially and temporally organized reaction fields, distinct standing wave modes, large-amplitude periodic acoustic pressure oscillations etc 44 . In fact, during the transition from S C to S TI via S IN , the disordered dynamics decreases continuously, while the ordered dynamics increases through the collective behaviour of small-scale structures 44,45 . This continuous evolution makes it difficult to identify the critical point of the system parameter or the onset of S TI , which is crucial for designing safe operating regimes of such complex spatiotemporal systems.…”