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FLAME DYNAMICS INTERMITTENCY IN THE BI-STABLE REGION NEAR A SUBCRITICAL HOPF BIFURCATION

[+] Author and Article Information
Dominik Ebi

Laboratory for Thermal Processes and Combustion, Paul Scherrer Institute, 5232 Villigen, Switzerland
dominik.ebi@psi.ch

Alexey Denisov

Institute of Thermal and Fluid Eng., School of Engineering, Hochschule für Technik FHNW, 5210 Windisch, Switzerland
alexey.denisov@fhnw.ch

Giacomo Bonciolini

CAPS Laboratory, Mechanical and Process Eng. Dept., ETH Zürich, 8092 Zürich, Switzerland
giacomob@ethz.ch

Edouard Boujo

CAPS Laboratory, Mechanical and Process Eng. Dept., ETH Zürich, 8092 Zürich, Switzerland
eboujo@ethz.ch

Nicolas Noiray

CAPS Laboratory, Mechanical and Process Eng. Dept., ETH Zürich, 8092 Zürich, Switzerland
noirayn@ethz.ch

1Corresponding author.

ASME doi:10.1115/1.4038326 History: Received August 10, 2017; Revised August 28, 2017

Abstract

We report experimental evidence of thermoacoustic bi-stability in a lab-scale turbulent combustor over a well-defined range of fuel-air equivalence ratios. Pressure oscillations are characterized by an intermittent behavior with "bursts", i.e. sudden jumps between low and high amplitudes occurring at random time instants. The corresponding probability density functions of the acoustic pressure signal show clearly separated maxima when the burner is operated in the bi-stable region. The gain and phase between acoustic pressure and heat release rate fluctuations are evaluated at the modal frequency from simultaneously recorded flame chemiluminescence and acoustic pressure. The representation of the corresponding statistics is new and particularly informative. It shows that the system is characterized, in average, by a nearly constant gain and by a drift of the phase as function of the oscillation amplitude. This finding may suggest that the bi-stability does not result from an amplitude-dependent balance between flame gain and acoustic damping, but rather from the non-constant phase difference between the acoustic pressure and the coherent fluctuations of heat release rate.

Copyright (c) 2017 by ASME
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