Suppression of chaotic thermoacoustic oscillations by external acoustic forcing

Previous studies have shown that periodic and quasiperiodic oscillations in self-excited thermoacoustic systems can be suppressed by applying acoustic forcing at a frequency sufficiently far from the natural frequency to cause a torus-death bifurcation to lock-in. However, whether this control strategy works on more complex thermoacoustic oscillations is not clear. In this experimental study, we investigate the forced synchronization of a ducted premixed flame oscillating chaotically. We find that the oscillation amplitude can be drastically reduced whenever lock-in is achieved, regardless of how close the forcing frequency is to the dominant frequency of the strange attractor. This implies that an open-loop controller designed for periodic or quasiperiodic oscillations should still be effective on chaotic oscillations, provided that lock-in is achieved. However, the reverse is not necessarily true: an open-loop controller designed for chaotic oscillations would amplify periodic and quasiperiodic oscillations if the forcing frequency was not sufficiently far from the natural frequency. It is important to recognize this difference when designing open-loop control strategies for complex thermoacoustic oscillations.