2017 Volume 59 Issue 187 Pages 24-32
Large-eddy simulation (LES) is performed to simulate high-frequency combustion instability in a single-element atmospheric combustor. Simulations are conducted for the corresponding combustion experiments, and the self-excited combustion instability observed in the experiments is successfully reproduced. The first tangential (1T) mode of the combustion chamber is excited in the LES, and the amplitude and frequency of the pressure fluctuations are consistent with the experimental observations. The 1T mode in the LES was observed at 1 kHz and the peak-to-peak amplitude was approximately 4% of time-averaged pressure. The coupling mechanism between the flame and acoustic velocity fluctuations is explored based on the LES results. The periodic ignition of the unburnt H2/O2 mixture produces a lifted combustion in a pulsating motion at the 1T mode frequency. This unsteady pulsating flame behavior is caused by the coupling between the fuel injection and the 1T mode acoustic oscillations. The Rayleigh index indicates that a primary driving factor of the instability is the acoustically coupled pulsating flame motion. The present results demonstrate that the LES can accurately capture the unsteady heat release and its coupling with pressure oscillations. The LES results clarify details of flame structures that are not completely understood solely from the experimental data, and therefore are valuable for understanding the coupling mechanism of the flame and acoustic mode in a combustion chamber.
