Effect of inlet flow turbulence on flame–vortex dynamics during thermo-acoustically induced flame flashback in a premixed dump combustor

The present article reports the investigation on the effect of inlet flow turbulence on flame–vortex dynamics during the thermo-acoustically induced flame flashback in a premixed dump combustor. The inlet turbulence intensity can be varied independently of the Reynolds number by using plates of different slot widths and is placed significantly upstream of the nominal flame-stabilization zone. The study aims to experimentally address the flame flashback behavior and the conventional combustion dynamics mechanisms involving flame–vortex interaction. The reacting flow-field is characterized using high-speed simultaneous measurement of dynamic pressure fluctuation with the time-resolved/phase-resolved visualization of flame and flow-field utilizing CH*/OH* chemiluminescence and particle image velocimetry. We note that higher turbulence intensity delays the onset of combustion dynamics and significantly influence the flame flashback behavior. In the present work, we observed two types of flame flashback behavior with large amplitude oscillations — (a) intermittent flame flashback, which relates to upstream flame displacement during certain phases of the acoustic pressure cycle and (b) permanent flame flashback, which results in flame quenching. The results reveals that the recirculation zone length plays a key role in determining the flame flashback. The role of enhanced turbulence is seen in two effects- (1) Dictating the length of the recirculation zone and (2) The modulation of the flame by the wake vortex, which correlates with the tendency of flame to flashback directly.