McIntosh A.

Pressure wave interactions with combustion has been a subject of a rich pedigree, beginning with Lord Rayleigh’s work in the nineteenth century and the known relevance of these effects in gas turbines and combustors where catastrophic failures can occur due to resonance. In this paper some of the fundamental length and time scales in pressure wave interactions with premixed flames are discussed. These basic relationships are fundamental in understanding the essentials of pressure wave interactions with combustion. There are three main types of interactions - long wavelength disturbances where the flame is essentially passive to the pressure eaves oscillations. Such frequencies would typically be in the 1 – 10 Hz range.. The second type of interactions are for higher frequency (hundreds of Hz ) pressure oscillations and in this case, though the flame movement is still essentially passive to the pressure changes, there can be changes in the energy fluctuations at the flame which then cause Rayleigh's criterion to be obeyed and energy to be added to the acoustic disturbance leading to resonance. For even higher frequencies still (the third region of interactions – KHz to MHz), the pressure wave disturbances can at this level severely disturb the premixed flame since the pressure disturbance length scale is on a par with the flame thickness, and the interactions can then become such as to single out a chemically derived resonant high frequency. Some detailed systems are considered where these basic principles are applied, and theoretical transfer functions for predicting the resonance characteristics for combustion devices are discussed. Some more recent interesting computational results from two dimensional interactions will also be remarked upon.