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Synchronization, the phenomenon of matching the rhythms of oscillators upon coupling, is ubiquitous in nature. Until now, one has held the notion that mutually coupled chaotic oscillators synchronize but retain their chaotic behavior, and so do coupled periodic oscillators. The possibility of alteration of the underlying dynamics of mutually coupled oscillators during synchronization seems to have received less attention. We present experimental evidence of synchronization, wherein the desynchronized coupled chaotic oscillators transition from a state of chaotic to periodic oscillations as they synchronize.

The thermoacoustic system we consider in this study is a turbulent flame combustor. The synchronization happens between the acoustic oscillations and heat release rate oscillations in this combustor. We carry out two separate analyses, one in the temporal domain and the other in the spatiotemporal domain. In the temporal analysis, the collective behavior of the spatially extended heat release rate oscillations is captured by summing up the intensity of light emitted from the flame. On the other hand, in the spatiotemporal analysis, we consider the spatial field of heat release rate oscillations as a set of coupled oscillators. The thermoacoustic system transitions from low amplitude chaotic oscillations to large amplitude periodic oscillations with a suitable change in some control parameter.

Our temporal analysis reveals that this transition culminates in a state of generalized synchronization (GS) of the two coupled oscillators, having gone through intermittent phase synchronization (IPS) and phase synchronization (PS). During IPS, the oscillators are periodic in the synchronized phase while harboring aperiodicity in the desynchronized phase. The spatiotemporal analysis, on the other hand, demonstrates the desynchronized nature of entire population of oscillators during the chaotic state, while a phase synchronized behavior is seen in the periodic state. An interesting feature of the spatiotemporal study is observed during intermittency, wherein the patches of synchronized periodic oscillations and desynchronized aperiodic oscillations simultaneously coexist in the reaction zone. This intermittent state resembles a chimera state. Additionally, in both the temporal and spatiotemporal cases, the amplitude of synchronous oscillations is found to be very large.

About Dr. Sujith
Dr. R. I. Sujith graduated with his B. Tech in Aerospace Engineering from the Indian Institute of Technology Madras in 1988 and M. S. (1990) and Ph. D. (1994) from the Georgia Institute of Technology, where he received the “top graduate student in the college of engineering” award. He worked as a post-doctoral fellow at the Georgia Institute of Technology in 1995. He joined the Department of Aerospace Engineering at the Indian Institute of Technology Madras in 1995 and is a full professor since 2006. He is also a Hans Fischer Senior Fellow of the Institute for Advanced Study (IAS) of the Technical University of Munich.

Sujith was the founding editor-in-chief of the International Journal of Spray and Combustion Dynamics from 2009-2015. He is a recipient of the Alexander Von Humboldt Fellowship. He is a fellow of the Indian National Academy of Engineering and the Indian Academy of Sciences, Bangalore, and has been conferred the title of “TUM ambassador” or the Technical University of Munich.