Optical and Numerical Analyses of Vortex-Flame Interaction Using Simultaneous and Two-Directional High-Speed Schlieren Photography and Discrete Vortex Method

结合以下两种设计方法，首次观测了平面丙烷-空气预混剪切层中火花点燃后火焰的传播特性；平面剪切层和同时双向纹影系统的声激励。为了获得平面预混剪切层中涡焰相互作用的特征火焰外观，引入了另一种特殊的点火极值点分配思想；一个在有组织涡流的中心，涡旋运动起着重要作用，另一个在两个相邻有组织涡流的中点，卷起运动占主导地位。在离散涡旋法描述的二维涡旋流场上，叠加火焰以恒定燃烧速度运动后的热膨胀，模拟了中点点火后火焰轮廓的二维变化。所得结果总结如下……(1)发现平面剪切流中有组织涡流中存在两种类型的火焰传播增强机制；一种是涡流运动引起的涡流破裂，另一种是卷起运动引起的涡流增强，它们对火焰传播增强过程的影响在数量上几乎相同。同时还发现，涡流助推是两种涡焰相互作用构型中的一种，利用所提出的离散涡方法可以定性地捕捉到。(2)模拟的火焰横向传播速度与实验得到的同步和双向高速纹影图像的轴向和横向传播速度吻合较好，但忽略斜压力矩、涡焰相互作用的三维性和火焰曲率的综合影响，会导致火焰传播速度的估计略高。结果表明，本文提出的二维离散涡旋法结合惠更斯原理对火焰在平面预混剪切层中的传播速度进行定性估计和建模是有效的，尽管为简化数值模拟引入了许多假设。(3)平面预混剪切层中火焰传播的增强效应由涡旋-火焰相互作用产生的物理增强效应和层流燃烧速度产生的化学增强效应组成。对于涡旋-火焰相互作用的两种构型，平面预混剪切层中涡旋相互作用下的火焰传播速度V_f由涡旋切向速度v_θ加上未受干扰火焰的传播速度（ρ_u/ρ_b）S_L给出，用下面的简单线性方程表示。V_f = v_θ+(ρ_u /ρ_b) S_L更少

The behavior of the propagating flame after the spark ignition in the plane propane-air premixed shear layer is first observed in this paper by combining the following two devised techniques; the acoustic excitation of the plane shear layer and the simultaneous and two-directional schlieren system. To obtain characteristic flame appearances due to the vortex-flame interaction in the plane premixed shear layer, another special idea of assigning two extreme points of ignition is introduced; one at the center of an organized eddy where the vortex motion plays an important role, and the other at the midpoint between two adjacent organized eddies where the rolling-up motion prevails. The two-dimensional change of flame outlines after the midpoint ignition is also simulated by superposing the flame movement with a constant burning velocity followed by thermal expansion on the two-dimensional vortex flow field described by the discrete vortex method. The results obtained are summarized as fol … More lows.(1) It is found that two types of the enhancement mechanisms of flame propagation exist among the organized eddies in the plane shear flow; one is the vortex bursting due to the vortex motion, the other is the vortex boosting due to the rolling-up motion, and exert quantitatively almost the same influences on the flame propagation enhancement process. Also found is that the vortex boosting which is one of the two configurations of vortex-flame interactions can be qualitatively captured by the proposed discrete vortex method.(2) The simulated lateral flame propagation velocities agree relatively well with the axial and lateral flame propagation velocities experimentally obtained from the simultaneous and two-directional high-speed schlieren images, although neglect of the combined effects of the baroclinic torque, the three dimensionality of vortex-flame interaction and the flame curvature leads to slight overestimation of the flame propagation velocity. This result verifies that the proposed two-dimensional discrete vortex method combined with Huygens' Principle is useful for qualitatively estimating and modeling the flame propagation velocity in the plane premixed shear layer, in spite of many assumptions introduced to simplify the numerical simulation.(3) The enhancement effects of flame propagation in the plane premixed shear layer are composed of the physical one due to the vortex-flame interactions and the chemical one through the laminar burning velocity. For both configurations of the vortex-flame interactions, the flame propagation velocity V_f with vortex interaction in the plane premixed shear layer is given by the vortex tangential velocity v_θ plus the propagation speed of the undisturbed flame (ρ_u/ρ_b)S_L, and expressed by the following simple linear equation.V_f=v_θ+(ρ_u/ρ_b)S_L Less