Effect of phase-shift feedback on thermoacoustic coupling

Abstract

The feedback interaction between unsteady heat release rate and combustor acoustics leading to self-excited oscillations is a well-known phenomenon, referred technically to as thermoacoustic instability. The phenomenon is a serious problem for practical applications as the resulting oscillations can adversely affect the stability and safety of the system. Flames, which are typically the source of unsteady heat release rate in practical combustors, are nonlinear elements in the thermoacoustic coupling and result in nonlinear dynamics such as sub/supercritical Hopf bifurcations, triggering, and chaotic oscillations, which characterizes thermoacoustic instability. The latter-chaos and known routes to chaos-are features that have recently been identified for thermoacoustic systems, but have been shown to be fundamental to the dynamics of practical systems. In previous work, variations of feedback control have been proposed for the active suppression of thermoacoustic oscillations and their efficacy has been demonstrated for prototypical as well as practical systems. Specifically, it has been shown that the Hopf bifurcation characteristics can be modified to increase the stable operational envelope of the system. In this paper, we will be presenting an extended investigation on phase-shift feedback control based on the full nonlinear system describing thermoacoustic instability in a Rijke tube, a representative system for studying thermoacoustic instability. The investigation will include results on changes in the stability of the system with variation in the system parameters-the heater power and heater location within the Rijke tube-and the parameters of feedback control. Copyright © (2018) by International Institute of Acoustics & Vibration.All rights reserved.