TY - GEN
T1 - Pulsation-amplitude-dependent flame dynamics of high-frequency thermoacoustic oscillations in lean-premixed gas turbine combustors
AU - Berger, Frederik M.
AU - Hummel, Tobias
AU - Schuermans, Bruno
AU - Sattelmayer, Thomas
N1 - Publisher Copyright:
Copyright © 2017 ASME.
PY - 2017
Y1 - 2017
N2 - This paper presents the experimental investigation of pulsationamplitude-dependent flame dynamics associated with transverse thermoacoustic oscillations at screech level frequencies in a generic gas turbine combustor. Specifically, the flame behavior at different levels of pulsation amplitudes 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, as well as flame-acoustic phase relations are evaluated. It is found that the unstable acoustic modes converge into a predominantly rotating character in the direction of the mean flow swirl. Furthermore, the flame modulation is observed to be in phase with the acoustic pressure at all levels of the oscillation amplitude. Second, distributed flame dynamics are investigated by means of visualizing the mean and oscillating heat release distribution at different pulsation amplitudes. The observed flame dynamics are then compared against numerical evaluations of the respective amplitude-dependent thermoacoustic growth rates, which are computed using analytical models in the fashion of a noncompact flame-describing function. While results show a nonlinear contribution for the individual growth rates, the 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 observations and analysis of amplitude-dependent flame modulation shows alternative paths to the explanation of mechanisms that might cause thermoacoustic saturation in high frequency systems.
AB - This paper presents the experimental investigation of pulsationamplitude-dependent flame dynamics associated with transverse thermoacoustic oscillations at screech level frequencies in a generic gas turbine combustor. Specifically, the flame behavior at different levels of pulsation amplitudes 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, as well as flame-acoustic phase relations are evaluated. It is found that the unstable acoustic modes converge into a predominantly rotating character in the direction of the mean flow swirl. Furthermore, the flame modulation is observed to be in phase with the acoustic pressure at all levels of the oscillation amplitude. Second, distributed flame dynamics are investigated by means of visualizing the mean and oscillating heat release distribution at different pulsation amplitudes. The observed flame dynamics are then compared against numerical evaluations of the respective amplitude-dependent thermoacoustic growth rates, which are computed using analytical models in the fashion of a noncompact flame-describing function. While results show a nonlinear contribution for the individual growth rates, the 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 observations and analysis of amplitude-dependent flame modulation shows alternative paths to the explanation of mechanisms that might cause thermoacoustic saturation in high frequency systems.
UR - http://www.scopus.com/inward/record.url?scp=85029046875&partnerID=8YFLogxK
U2 - 10.1115/GT201763997
DO - 10.1115/GT201763997
M3 - Conference contribution
AN - SCOPUS:85029046875
T3 - Proceedings of the ASME Turbo Expo
BT - Combustion, Fuels and Emissions
PB - American Society of Mechanical Engineers (ASME)
T2 - ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition, GT 2017
Y2 - 26 June 2017 through 30 June 2017
ER -