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

Author:

Berger Frederik M.1,Hummel Tobias2,Schuermans Bruno3,Sattelmayer Thomas1

Affiliation:

1. Lehrstuhl für Thermodynamik, Technische Universität München, Garching 85748, Germany e-mail:

2. Lehrstuhl für Thermodynamik, Technische Universität München, Garching 85748, Germany; Institute for Advanced Study, Technische Universität München, Garching 85748, Germany e-mail:

3. Institute for Advanced Study, Technische Universität München, Garching 85748, Germany; GE Power, Baden 5401, Switzerland e-mail:

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 levels of pulsation amplitudes is assessed and interpreted. Spatial dynamics of the flame are measured by imaging the OH⋆ chemiluminescence (CL) 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 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 displacement 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.

Funder

Bundesministerium für Wirtschaft und Technologie

Publisher

ASME International

Subject

Mechanical Engineering,Energy Engineering and Power Technology,Aerospace Engineering,Fuel Technology,Nuclear Energy and Engineering

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