Abstract: The transition in dynamics from low-amplitude, aperiodic, combustion noise to high-amplitude, periodic, combustion instability in confined, combustion environments was studied experimentally in a laboratory-scale combustor with two different flameholding devices in a turbulent flow field. We show that the low-amplitude, irregular pressure fluctuations acquired during stable regimes, termed ‘combustion noise’, display scale invariance and have a multifractal signature that disappears at the onset of combustion instability. Traditional analysis often treats combustion noise and combustion instability as acoustic problems wherein the irregular fluctuations observed in experiments are often considered as a stochastic background to the dynamics. We demonstrate that the irregular fluctuations contain useful information of prognostic value by defining representative measures such as Hurst exponents that can act as early warning signals to impending instability in fielded combustors. This talk does not need any prior knowledge of multifractality.

Biosketch: 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 has been conferred the title of “TUM ambassador” or the Technical University of Munich. Sujith brought dynamical systems theory and complex systems theory to thermoacoustics. This has paid rich dividends both in understanding the phenomena, and from an industrial perspective of obtaining precursors to these undesirable transitions.

For more information, please contact Prof. Ann Karagozian at ark@seas.ucla.edu
All faculty, students, AFRL researchers, and guests are welcome to this event (refreshments will be served)