Predicting the Amplitude of Thermoacoustic Instability Using Universal Scaling Behaviour

Abstract

The complex interaction between the turbulent flow, combustion and the acoustic field in gas turbine engines often results in thermoacoustic instability that produces ruinously high-amplitude pressure oscillations. These self-sustained periodic oscillations may result in a sudden failure of engine components and associated electronics, and increased thermal and vibra-tional loads. Estimating the amplitude of the limit cycle oscillations (LCO) that are expected during thermoacoustic instability helps in devising strategies to mitigate and to limit the possible damages due to thermoacoustic instability. We propose two methodologies to estimate the amplitude using only the pressure measurements acquired during stable operation. First, we use the universal scaling relation of the amplitude of the dominant mode of oscillations with the Hurst exponent to predict the amplitude of the LCO. We also present a methodology to estimate the amplitudes of different modes of oscillations separately using ‘spectral measures’ which quantify the sharpening of peaks in the amplitude spectrum. The scaling relation enables us to predict the peak amplitude at thermoacoustic instability, given the data during the safe operating condition. The accuracy of prediction is tested for both methods, using the data acquired from a laboratory-scale turbulent combustor. The estimates are in good agreement with the actual amplitudes.

Rijke tube: A nonlinear oscillator

“…In thermoacoustic systems, different measures have been invented to obtain early warning signals that predict the occurrence of thermoacoustic instability. 340 These measures exhibit a drastic change in their values prior to the onset of such instability. Tracking the changes in the measure can help us to provide early warning for impending instability.…”

Rijke tube: A nonlinear oscillator

“…In thermoacoustic systems, different measures have been invented to obtain early warning signals that predict the occurrence of thermoacoustic instability 331 . These measures exhibit a drastic change in their values prior to the onset of such instability.…”