Experimental and numerical investigation of thermo-acoustic instability in a liquid-fuel aero-engine combustor at elevated pressure: Validity of large-eddy simulation of spray combustion

The feasibility of applying the large-eddy simulation (LES) of spray combustion to the investigation of the thermo-acoustic instability mechanisms in practical aero-engine combustors was examined, employing experimental data obtained from optical measurements. Single sector combustion tests using a staged fuel injector were conducted at the JAXA high temperature and pressure combustion test facility. An unstable operating condition exhibiting strong self-excited thermo-acoustic instability with a peak frequency of approximately 500 Hz and an amplitude more than 40 kPa was chosen for measurements of the dynamic pressure, in addition to OH-PLIF and OH∗ chemiluminescence studies. LES calculations were performed under the same conditions and the use of LES was validated based on comparisons of results with experimental data, considering the dynamic pressure and unsteady flame behaviors. In addition, a more detailed investigation was performed with the LES data, focused on unsteady characteristics such as velocity, evaporation rate, equivalence ratio and heat release rates. In general, LES was found to successfully reproduce the experimentally observed unsteady characteristics of pressure and flame structures during thermo-acoustic instability, though there were several discrepancies between LES and experimental results with regard to the oscillation amplitude and local flame behavior, such as the periodical flame flashback. In the LES data, the time evolution of the product of the flame surface area and the flame-area-averaged equivalence ratio were in good agreement with the overall heat release rate variations, suggesting a simple dominant mechanism for the thermo-acoustic instability. These results provide evidence for the feasibility of employing LES as a means of further exploring the effects of key physical parameters, such as the spatial distribution of fuel and its temporal variations, on combustion instability.