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research-article

Pulsation-Amplitude-Dependent Flame Dynamics of High-Frequency Thermoacoustic Oscillations in Lean-Premixed Gas Turbine Combustors

[+] Author and Article Information
Frederik M. Berger

Lehrstuhl für Thermodynamik Technische Universität München 85748 Garching, Germany
berger@td.mw.tum.de

Tobias Hummel

Lehrstuhl für Thermodynamik Technische Universität München 85748 Garching, GermanyInstitute for Advanced Study Technische Universität München 85748 Garching, Germany
hummel@td.mw.tum.de

Bruno Schuermans

Institute for Advanced Study Technische Universität München 85748 Garching, GermanyGE Power 5401 Baden, Switzerland
bruno.schuermans@ge.com

Thomas Sattelmayer

Lehrstuhl für Thermodynamik Technische Universität München 85748 Garching, Germany
sattelmayer@td.mw.tum.de

1Corresponding author.

ASME doi:10.1115/1.4038036 History: Received July 03, 2017; Revised August 01, 2017

Abstract

This paper presents the experimental investigation of pulsation-amplitude-dependent flame dynamics associated with transverse thermoacoustic oscillations at screech level frequencies in a generic gas turbine combustor. Specifically, the flame behavior at different pulsation amplitude levels is assessed and interpreted. Spatial dynamics of the flame are measured by imaging the OH* chemiluminescence signal synchronously to the dynamic pressure at the combustor's face plate. First, linear thermoacoustic stability states, modal dynamics, and flame-acoustic phase relations are evaluated. It is found that the unstable acoustic modes converge into a predominantly rotating character with the mean flow swirl. Furthermore, the flame modulation is observed to be in phase with the acoustic pressure at all oscillation amplitude levels. Second, distributed flame dynamics are investigated by visualizing the mean and oscillating heat release distribution at different pulsation amplitudes. The observed flame dynamics are then compared against numerical evaluations of respective amplitude-dependent thermoacoustic growth rates, which are computed using analytical models in the fashion of a non-compact flame-describing function. While results show a non-linear contribution for the individual growth rates, superposition of flame deformation and displacements balances out to a constant flame driving. This latter observation contradicts the state-of-the-art perception of root-causes for limit-cycle oscillations in thermoacoustic gas turbine systems, for which the heat release saturates with increasing amplitudes. Consequently, the systematic analysis of amplitude-dependent flame modulation shows alternative paths to the explanation of mechanisms that might cause thermoacoustic saturation in high frequency systems.

Copyright (c) 2017 by ASME
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