Reheat buzz: an acoustically coupled combustion instability. Part 2. Theory

Reheat buzz is a low-frequency instability of afterburners. It is caused by the interaction of longitudinal acoustic waves and unsteady combustion. Similar combustion instabilities occur in laboratory rigs. A theory is developed to determine the frequency and mode shape of the instability and is tested by comparison with the experimental results described in Part1. The predicted and measured frequencies are found to be within 6 Hz (7%) of each other. The theory is able to predict the observed variation of frequency with equivalence ratio, inlet Mach number and geometry.