Intrinsic thermoacoustic modes and their interplay with acoustic modes in a Rijke burner

To this end, the system is examined for a range of time delays, temperature ratios and reflection coefficients as adjustable parameters. A linear acoustic network model is used and all modes with frequency below the cut-on frequency for non-planar acoustic waves are considered.

The results show that when reflection coefficients are reduced, the presence of a pure ITA mode limits the reduction in the growth rate that usually results from a reduction of the reflection coefficients. In certain conditions, the growth rates can even increase by decreasing reflections. As the time delay of the flame and thus the ITA frequency decreases, the acoustic modes couple to and subsequently decouple from the pure ITA modes.