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This paper demonstrates cross-frequency coupling between pressure, heatrelease rate, fuel spray and velocity oscillations in a model aeronautical gasturbine combustor operating at a pressure of approximately 10 atm. Heat releaserate was characterized by 10 kHz chemiluminescence (CL) imaging of severalspecies. Stereoscopic particle image velocimetry and laser Mie scattering fromthe fuel droplets were used to measure the gas velocity and spray dynamics,respectively, at 5 kHz. The pressure fluctuations were dominated byoscillations at a frequency $f_0$, whereas the spray, CL and velocityoscillated at approximately $2f_0$. All of these oscillations werenonstationary, exhibiting changes in frequency and amplitude. Comparing thetime evolution of the dominant frequencies and amplitudes indicates a behaviorconsistent with mutually coupled self-oscillators; the observed dynamics of the1:2 super-harmonic coupling is consistent synchronization via oscillationdeath. Furthermore, increases in the frequency of the ca. $f_0$ velocityoscillations away from the harmonic ratio (increased frequency detuning) werecorrelated with decreases in the power of the $f_0$ pressure oscillations. Thecorresponding nonreacting flow had a natural hydrodynamic mode at a frequencyslightly greater than $2f_0$. Hence, the data are consistent with the $f_0$acoustic mode "pulling" the hydrodynamic frequency towards the super-harmonicratio.

Cross-Frequency Coupling During Thermoacoustic Oscillations in a Pressurized Aeronautical Gas Turbine Model Combustor