Cross-frequency coupling during thermoacoustic oscillations in a pressurized aeronautical gas turbine model combustor

This paper demonstrates cross-frequency coupling between pressure, heat release rate, fuel spray and velocity oscillations in a model aeronautical gas turbine combustor operating at a pressure of approximately 10 atm. Heat release rate was characterized by 10 kHz chemiluminescence (CL) imaging of several species. Stereoscopic particle image velocimetry and laser Mie scattering from the fuel droplets were used to measure the gas velocity and spray dynamics, respectively, at 5 kHz. The pressure fluctuations were dominated by oscillations at a frequency f 0 , whereas the spray, CL and velocity oscillated at approximately 2 f 0 . All oscillations were non-stationary, exhibiting temporal changes in frequency and amplitude. Comparing the time evolution of the dominant frequencies and amplitudes indicated a behaviour consistent with mutually coupled and unsynchronized self-oscillators; the observed dynamics are consistent with variations in reactive coupling strength. Specifically, increases in the frequency of the ca . 2 f 0 velocity oscillations away from the 1:2 harmonic ratio (increased frequency detuning) were correlated with decreases in the power of the f 0 pressure oscillations. The corresponding nonreacting flow had a natural hydrodynamic mode at a frequency slightly greater than 2 f 0 . Hence, the data are consistent with the f 0 acoustic mode ?pulling? the hydrodynamic frequency towards the 1:2 harmonic ratio. ? 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

This study investigates cross-frequency coupling between different signals in a model aeronautical gas turbine combustor, with non-stationary oscillations exhibiting temporal changes in frequency and amplitude. The experimental data supports the notion of mutually coupled self-oscillators.