Study on The Flame Behaviors in A Centrifugal Acceleration Environment of Solid Vortex

由于旋涡中存在强烈的湍流，火焰在旋涡中的传播表现出复杂的行为。本文利用带混合气旋转的旋转燃烧装置，研究了旋转流动环境对火焰行为的实际影响。实验结果表明，在强烈的旋转流动中，由于火焰核向中心的快速运动和湍流火焰锋的层叠化，旋涡增强燃烧并不总是能够实现。实验结果表明：(1)在容器中心点燃的燃烧气体迅速膨胀，由于未燃烧气体和燃烧气体之间存在的机械不平衡所引起的干扰，可能会抑制火焰的生长，并可能导致火焰熄灭，这取决于条件。(2)靠近容器壁点火时，火焰迅速向容器中心移动，火焰区比中心点火时发展得更快。但是，湍流火焰区的层叠化很快就出现了与中心点火相似的过程。虽然消光半径比中心点火大，但消光时间（燃烧周期）仍与中心点火大致相同。(3)消光极限似乎由火焰传播速度与火焰对流速度的相对关系决定。随着Vc/Vf比值的增大，消光趋势变得明显。(4)除转速影响外，预热区厚度、燃烧速度和与火焰结构有关的刘易斯数对燃烧的影响程度较大。

Flame propagation in a swirl flow shows complicated behaviors due to the intense turbulence accompanied by the swirl. In this study, by making use of the rotary combustion device which rotates with mixture in it, the real effects of the rotating flow environments on the flame behaviors are investigated. The experimental results make clear that the enhanced combustion by the swirl cannot always be realized because of the rapid motion of a flame kernel toward the center and the laminarization of turbulent flame front in the intense rotating flow. The experimental results are summarized as follows :(1)A rapid expansion of the burned gas ignited at the vessel center may suppress the growth of flame due to disturbance caused by a mechanical non-equilibrium existing between unburned and burned gas, and may cause a flame extinction, depending on the condition.(2)In the case of the ignition near the vessel wall, flame quickly moves to the vessel center and the flame zone develops more than for the central ignition. But, the laminatization of the turbulent flame zone soon appears to follow the similar process to the central ignition. Although the extinction radius becomes larger than that for the central ignition, the extinction time(burnig period)still remains approximately the same as that for the central ignition.(3)The extinction limit seems to be determined by the relative relation between a flame propagation speed and a flame convection speed. The extinction tendency becomes considerable with the increase of the ratio, Vc/Vf.(4)With the exception of the influence of the rotation speed, the degree of influence considerably depends on the preheat zone thickness, the burning velocity, and the lewis number that are related to the flame structure.