This paper describes an experimental investigation on the time dependent lift-off behaviors of flames stabilized in axisymmetric turbulent jet. Reactive mie scattering techniques and high speed CCD photography were employed to investigate the behaviors of lifted flame and the flow field in the near-nozzle region of isothermal jets, attached flames, and lifted flames. Using the visualization techniques, it is observed that the lowest point of flame base of the lifted flame rotates around the periphery of the jet, and this rotating behavior is confirmed by measuring temperature fluctuation at the flame base of the lifted flame. Thus, this rotating behavior gives rise to azimuthal variations in the instant lift-off height. And it is found that there exist large scale vortex motion in the isothermal region of the lifted flame through visualizing various entrainment patterns of the ambient air into the jet fluid. These large scale helical vortex field of the jet in the relative near field of the nozzle bring about the rotating behavior of the lifted flame base. Also, in this study, it is suggested that the lobe size as well as the local jet diameter should be considered for determining the large scale mixing time in connection with the large scale structural mixing model of the lifted flame. Obviously, the physical mechanism of the lifted flame is yet sufficiently well understood, hence the present investigation was performed in order to provide more detailed understandings of the lift-off behaviors in relation to large scale turbulent structures.
