Experimental measurement of the flow field of a swirling flame under large amplitude acoustic forcing

The dynamic of a swirling flame under high acoustic perturbation characterizes its non-linear acoustic response. Here, it shows that the time-dependent flow field of a swirling flame under large amplitude acoustic forcing, measured by high-repetition rate pulse burst laser Particle Image Velocimetry (PIV) technique, is highly non-linear. The periodic vortex structures formed in the inner and outer shear layers of the swirling flame can interact with the flame front and flow field though distinct manners:the vortex ring formed in the outer shear layer folds the flame front and alters the flame heat release rate; the vortex ring formed in the inner shear layer mainly affects the velocity distribution in the recirculation zone. We quantitatively analyzed the effects of the outer/inner vortex rings, including the trajectory, vorticity, circulation and size. We found that exit velocity and acceleration are the main factors that determine the formation and release of the out shear layer vortex ring.