Theoretical investigation on the moving flame–sound interaction in a closed-open combustor

Abstract

Self-excited thermoacoustic instability is highly undesirable for power generation gas turbines, aero-engine afterburners, liquid-fuelled ramjet, and rocket motors. It is typically generated due to the constructive interaction between acoustic perturbations and the flame. It is a general practice to assume that the flame is non-moving and the combustor is typically assumed to be acoustically opened. In this work, we consider a closed-open thermoacoustic combustor with a moving flame. To better understand the physics between the acoustic disturbances and the moving flame, we theoretically investigate the moving flame-sound interaction. We find that the presence of the moving flame can amplitude the gaseous oscillations. Furthermore, the amplification process is shown to depend on the laminar burning velocity on the temperature and density of the combustible gas mixture into which the flame propagates. The sound source is shown to be the quadrupole mode. It radiates very little energy, if the flame dimensions are smaller than the wavelength of the sound produced. The present work shed lights on the sound generation from a moving flame and its interaction with sound.