TURBULENT BLUFF-BODY FLAMES CLOSE TO STABILITY LIMITS REVEALED BY COUPLING OF HIGH SPEED OPTICAL DIAGNOSTICS

The understanding of flame stabilization is a requirement for the development of innovative combustion regimes associated to low pollutant emissions and high efficiency. Bluff-body burners are well adapted for the stabilization of turbulent non-premixed flames near extinction limit. In the present work, the stabilization mechanisms involved in turbulent bluff-body flames are investigated by means of time-resolved optical diagnostics. High-Rate Particle Image Velocimetry (HR-PIV) is coupled simultaneously to High-Rate flame imaging in order to point out the correlation between the aerodynamic fields and the flame structures from images time series. A periodic ejection of burning pockets is observed from the recirculation zone established at the burner exit to the base of the main lifted flame. The characteristic frequencies are determined by extracting local velocities and flame emission with time. This periodic behaviour is correlated to the intermittency of the aerodynamic structures. These results provide a better understanding of the physical phenomena controlling the stabilization of this turbulent flame.