Large eddy simulations of spray combustion instability in an aero-engine combustor at elevated temperature and pressure

Abstract

Large eddy simulations (LES) of self-excited spray combustion instability in an aero-engine combustor are performed to investigate the mechanisms of combustion instability. Three spray flames with different droplet diameters and wall boundary conditions are trigged to be unstable explicitly. The dominant oscillation frequencies are around 1437 Hz, 1314 Hz and 1200 Hz in the three cases, respectively. The pressure and heat release rate oscillate with the same frequency and phase, which shows that the combustion instability is mainly caused by thermo-acoustic interaction. In the spray combustion instability process, flame surfaces collapse and merge with the adjacent flame surfaces to form burning pockets. The dominant mechanisms that drive the spray combustion instability are attributed to the formation and annihilation of burning pockets. The oscillation amplitudes are affected by the initial droplet diameter and wall boundary condition. When the initial averaged droplet diameter increases from 15 μm to 20 μm or the cooling air is removed from the combustor, the oscillation amplitudes decrease. These results give new insights into more complex mechanisms and influencing factors of self-excited spray combustion instability.