Mitigating self-excited flame pulsating and thermoacoustic oscillations using perforated liners

Open-loop control of self-excited flame pulsating oscillations and thermo-acoustic instability is considered in this work. The performance of the control strategy is numerically evaluated in a 2D Rijke-type combustor with a perforated pipe implemented. It is found that approximately 38 dB sound pressure level (SPL) reduction can be achieved by actively tuning the cooling flow through the perforated pipe. Furthermore, the vorticity-induced damping performance is contributing to the breaking up of flame-acoustics coupling. However, the shedding of vortices is not uniformly distributed along the perforated pipe. To apply the control strategy in practice and to validate the findings, experimental studies are performed on a customerdesigned Rijke-type combustor with a perforated liner implemented. To mimic practical engines, a cooling flow generated by a centrifugal pump is provided to pass through the perforated pipe. Properly tuning the cooling flow rate is found to lead to the unstable combustor being successfully stabilized. SPL is reduced by approximately 35 dB at omega(1) /2 pi approximate to 245 Hz, and harmonic thermoacoustic modes are completely attenuating. Further study is conducted by suddenly removing the perforated pipe section. The combustion system is found to be associated with not only classical thermo-acoustic limit cycle oscillations with a dominant mode at 2.45 x 10(2) Hz, but also beating oscillations at 1.4 x 10( )(0)Hz. It is revealed that increasing acoustic losses by implementing the perforated pipe is another critical mechanism contributing to attenuating flame pulsating instability. The present work opens up an applicable means to attenuate both selfexcited high-frequency thermoacoustic and low-frequency flame pulsating oscillations. (C) 2019 Science China Press. Published by Elsevier B.V. and Science China Press. All rights reserved.