Detailed Image Analysis of Vortex-Flame Interaction under Acoustic Excitation of Coherent Structure Characterized by Geometrical Configuration

在实际的湍流流场中，由于其自身的几何构型不同，存在着多种拟序结构，如射流、尾迹和平面剪切层等。由于这些流场被用作实际湍流燃烧的基本流场，因此湍流燃烧中涡流-火焰相互作用的详细光学观察和图像处理能够模拟基本火焰结构。为了使后者成为可能，各种设备是必要的光学观测和图像处理。在2006年的第一期调查中，相干结构的声学激发已经被引入，使其引人注目，并使光学观测变得容易，而详细的PIV测量和图像处理是为了估计斜压扭矩对涡度守恒方程的影响。在2007年的最后一期研究中，对斜压力矩在火焰-气流相互作用中的具体作用进行了研究。 ...更多信息 艾德使用不可压缩的二维射流，在上述流动中是最简单的。利用PIV测速仪，以直径约1 μm的二氧化钛粉末和熏香烟为跟踪粒子，对微重力（0.1m/s ~ 2）和正常重力下二维涡旋喷射到均匀和非均匀密度场中的行为进行了跟踪和分析。通过对实验装置的改进，如采用塔式系统实现室内微重力条件，采用PIV成像系统研究斜压力矩对涡-火焰相互作用的微弱影响，发现由于密度梯度和压力梯度的共同影响，在涡-火焰相互作用的边界区域沿着明显地产生了对称涡量，并且涡流内的流速在涡流产生的边界区域上不连续地减小。最后还发现，在不可避免地产生陡峭密度梯度的火焰区，斜压力矩对涡-火焰相互作用的影响有选择地增强。

Depending on their own geometric configurations, many types of coherent structures exist in the practical turbulent flow fields, such as jets, wakes and plane shear layers. Since these flow fields are employed as fundamental flow fields for practical turbulent combustion, detailed optical observations and image processing of vortex-flame interaction in the turbulent combustion enable modeling of basic flame structure. To make the latter possible, a variety of devices is necessary concerning optical observations and image processing. During the first term of this investigation, 2006, acoustic excitation of coherent structure has been introduced to make it conspicuous and to make optical observation easy, whereas detailed PIV measurements and their image processing are made to estimate the effects of baroclinic torque on the vorticity conservation equation. In the final term of this investigation, 2007, the concrete roles of baroclinic torque in the flame-flow interaction have been studi … More ed using an incompressible two-dimensional jet, being most simple among the above-mentioned flows. By means of PIV velocimeter using titanium-oxide powder and smoke of an joss stick of about 1 μm diameter as tracking particles, the behaviors of a single two-dimensional vortex ejected into both uniform and non-uniform density fields under micro-gravity of 0.1 m/s2 have been tracked and analyzed, as well as those under normal gravity. Some devices and improvements have been made, such as a tower system to realize the condition of micro-gravity in the normal room situation and an original PIV-imaging system for making clear the weak effects of baroclinic torque on vortex-flame interaction.It was found that, due to the combined influence of density-gradient and pressure-gradient, a symmetric vorticity is clearly generated along the boundary region of the vortex, and that the flow velocity within the vortex decreases discontinuously across the boundary region of vorticity generation. Also found was that, finally, the effects of baroclinic torque on vortex-flame interaction are selectively enhanced in the flame zone where a steep density gradient inevitably is produced Less