Multifractal characteristics of combustor dynamics close to lean blowout

• Published in: Journal of fluid mechanics 2015-12, Vol.784, p.30-50
• Main Authors: Unni, Vishnu R., Sujith, R. I.
• Format: Article
• Language: English
• Subjects: Acoustics; Combustion; Fluid mechanics; Fluidized bed combustion; Turbulent flow
• ISSN: 0022-1120; 1469-7645
• DOI: 10.1017/jfm.2015.567

In classical literature, blowout is described as loss of static stability of the combustion system whereas thermoacoustic instability is seen as loss of dynamic stability of the system. At blowout, the system transitions from a stable reacting state to a non-reacting state, indicating loss of static stability of the reaction. However, this simple description of stability margin is inadequate since recent studies have shown that combustors exhibit complex nonlinear behaviour prior to blowout. Recently, it was shown that combustion noise that characterizes the regime of stable operation is itself dynamically complex and exhibits multifractal characteristics. Researchers have already described the transition from combustion noise to combustion instability as a loss of multifractality. In this work, we provide a multifractal description for lean blowout in combustors with turbulent flow and thus introduce a unified framework within which both thermoacoustic instability and blowout can be described. Further, we introduce a method for predicting blowout based on the multifractal description of blowout.