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"Secondary Bifurcations and Explosive Synchronization
in Turbulent Reacting Flow Systems"

by

Prof. R.I. Sujith

Head of the Center of Excellence | IIT Madras

Tuesday, September 26
11:30 to 12:30pm
Food Processing Technology Auditorium

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Meeting ID: 256 640 951 132
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About the Seminar: 
Abrupt transitions from a stable operation to oscillatory instability is a significant problem in engineering systems such as thermoacoustic and aeroacoustic systems. Earlier studies in turbulent combustors have reported that the onset of combustion-driven oscillations is always presaged by intermittent bursts of high amplitude periodic oscillations that appear in a near-random fashion amidst regions of aperiodic low-amplitude fluctuations. Intermittency leads to the appearance of a sigmoid-like transition to thermoacoustic instability in the root mean square (rms) of the acoustic pressure fluctuations. However, abrupt transitions via secondary bifurcations have been reported recently in turbulent thermoacoustic systems. We present the observation of abrupt transition in three disparate turbulent thermoacoustic systems: an annular combustor, a swirl-stabilized combustor, and a preheated bluff-body stabilized combustor. Using a low-order stochastic thermoacoustic model, we show that the reported abrupt transitions occur when an initially stable, supercritical limit cycle becomes unstable, leading to a secondary bifurcation to a large amplitude limit cycle. We show that the chaotic heat release rate fluctuations from turbulent flamelets synchronize explosively leading to an abrupt transition to a periodic state. Furthermore, we discovered abrupt transition from one limit cycle oscillation to another in an aeroacoustic system during the shift in the whistling frequency.

About the Speaker: 
Prof. R. I. Sujith received his B. Tech in Aerospace Engineering from IIT Madras in 1988. He then graduated with an M. S. (1990) and Ph. D. (1994), from the Georgia Institute of Technology. He joined IIT Madras as a faculty member at the Department of Aerospace Engineering in 1995. Currently, he heads the Center of Excellence (CoE) to study Critical Transitions in Complex Systems (CTCS) at IIT Madras. Sujith is a recipient of the Alexander von Humboldt Fellowship and the Hans Fischer Senior Fellowship of the Institute for Advanced Study (IAS) of TU Munich. Sujith was the founding Editor-in-Chief of the International Journal of Spray and Combustion Dynamics and is currently a member of the editorial advisory board of Chaos: An Interdisciplinary Journal of Nonlinear Science. He has been awarded the Swarnajayanti and J. C. Bose Fellowships by the Department of Science and Technology of the Government of India. He is a Distinguished Fellow of the International Institute of Acoustics and Vibration (IIAV) and a Fellow of the Combustion Institute, the Indian National Academy of Engineering and the Indian Academy of Sciences. He has been recently elected as an International Member of the US National Academy of Engineering. He has been conferred with the life-time achievement award of IIT Madras. Prof. Sujith’s research interests are in the area of complex systems theory in general and thermoacoustic instability in particular.