Investigation of Interaction between Diffusion Flame and Vortex by Advanced Laser Image Diagnostics

火焰-旋涡相互作用是分析湍流火焰微观结构和熄灭的重要因素，因而受到人们的广泛关注。采用瑞利散射和激光诱导荧光（LIF）相结合的方法，对燃料侧声激励诱导的大尺度涡与氮气稀释的氢气（H2 30%+ N2 70%）扩散火焰相互作用过程中的二维温度分布和OH-LIF分布进行了瞬态和同步测量。研究了火焰与涡流相互作用过程中扩散火焰熄灭和中断的动力学行为。本研究中观察到的结果描述如下。(1)在燃料射流速度波动较大的情况下，在涡流的凸起和圆周部分，反应区的温度和OH-LIF变得显著降低，在该部分存在涡流的温度层，并导致OH-LIF和温度层变薄，从而导致火焰熄灭。(2)在对燃料射流施加较大的速度波动的情况下，反应区在涡流的圆周部分或背面被中断。通过涡流的卷起运动，已燃气体被从上游反应区拉起，并在火焰内部形成高温区，已燃气体随时间局部消散。消散的已燃烧气体减少了进入周向反应区的燃料供应，并引起反应区的中断。边缘火焰形成在火焰内部和涡流的圆周部分处。

The flame-vortex interaction has attracted research attentions because it constitutes important elements for analyzing the microscopic turbulent flame structure and extinction. Instantaneous and simultaneous measurements of two-dimensional temperature and OH-LIF profiles by combining Rayleigh scattering with laser induced fluorescence (LIF) were demonstrated in nitrogen-diluted hydrogen (H_2 30 % + N_2 70 %) diffusion flame interacted with a large scale vortex induced by the acoustic excitation at the fuel side. It is investigated to analyze dynamic behavior of the diffusion flame extinction and interruption during the flame-vortex interaction processes. The results observed in this study are described as follows.(1) In the case that a large velocity fluctuation is given to the fuel jet, the temperature and the OH-LIF at the reaction zone become significantly lowered at the convex and circumferential part of the vortex where temperature layer of the vortex exists and the thinning of the OH-LIF and temperature layer and the consequent flame extinction are induced.(2) In the case that a larger velocity fluctuation is given to the fuel jet, the reaction zone is interrupted at the circumferential part or backside of the vortex. By curling up motion of the vortex, the burnt gas is pulled up from the upstream reaction zone and makes high temperature region inside the flame and the burnt gas dissipates locally with time. The dissipated burnt gas reduces the supply of fuel into circumferential reaction zone and interruption of the reaction zone is induced. The edge flames are formed inside the flame and at the circumferential part of the vortex.