  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 $2f_0$. All of these oscillations were
nonstationary, exhibiting changes in frequency and amplitude. Comparing the
time evolution of the dominant frequencies and amplitudes indicates a behavior
consistent with mutually coupled self-oscillators; the observed dynamics of the
1:2 super-harmonic coupling is consistent synchronization via oscillation
death. Furthermore, increases in the frequency of the ca. $f_0$ velocity
oscillations away from the 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 $2f_0$. Hence, the data are consistent with the $f_0$
acoustic mode "pulling" the hydrodynamic frequency towards the super-harmonic
ratio.
