Thermoacoustic Coupling Mechanism of Combustion Instability in a Continuously Variable Resonance Combustor

Longitudinal self-excited combustion instability in Continuously Variable Resonance Combustor is numerically reproduced by changing the oxidizer inlet temperature from 700K to 720K. Modal and Causal analyses using sparsity-promoting Dynamic Mode Decomposition and Permutation Transfer Entropy, respectively, are conducted to understand the mechanism of the combustion instability. Through the modal analysis, it is found that the heat release rate and the acoustic mode are in phase when the combustion instability reaches to the stationary condition. Overlap between the acoustic antinode and the peak of the heat release rate are larger for 720K case where the large combustion instability is obtained, which corresponds to the combustion instability criteria based on the Rayleigh index. It is also found that the fluctuation of the heat release rate is correlated to the pulsating motion of the oxidizer. According to the causality analysis, the heat release rate is found to be unilaterally correlated to the acoustic mode.