Intermittency—A State That Precedes Thermoacoustic Instability and Blowout in Turbulent Combustors

Abstract

Let us recall from Chaps. 3 and 4 that during the onset of thermoacoustic instability in laminar systems, the dynamics of the acoustic pressure fluctuations transitions from a state of fixed point to limit cycle oscillations. We observed that this transition in the acoustic pressure fluctuations is direct without the presence of an intermediate state. Additionally, the transition is accompanied by a sudden jump in the pressure amplitude for subcritical Hopf bifurcation or a gradual increase in the pressure amplitude for supercritical Hopf bifurcation. In the present chapter, we will focus on understanding the dynamical changes happening in the acoustic pressure fluctuations during the occurrence of thermoacoustic instability in turbulent thermoacoustic systems. We will first systematically characterize the properties of acoustic pressure fluctuations during the states of stable operation and unstable operation of a turbulent combustor. Subsequently, we will discuss the characteristics of the dynamical transition from stable to unstable operation, and also the properties of the state of intermittency. We will also shed light on the route to the occurrence of another undesired dynamic phenomenon called lean flame blowout. Finally, we will present a universal scaling observed in acoustic pressure fluctuations during the onset of thermoacoustic instability in different turbulent combustors.