Acoustic Excitation of Organized Eddy Structure and Dual diffusion Flames Behind a Rear-Facing Simicircular Cylinder

实验研究了后半圆形燃油喷嘴后两种类型的双扩散火焰；一种是由燃油喷嘴低速侧的普通层流扩散火焰和高速侧的提升火焰组成的平面扩散火焰，另一种是由燃油喷嘴两侧的两个提升火焰组成的崖体稳定尾迹火焰。将计算机辅助锁相平均法（简称CAPLA法）与声激励相结合，研究了声激励对火焰结构的影响，以及有组织涡流和涡流火焰形成过程的相位特征。在燃烧通道的高速侧壁上安装了一个固定频率为300Hz的平板扬声器，进行声激励。根据火焰的闪影图发现，声激励使旋涡火焰轮廓清晰，且旋涡的组织迅速清晰，使激发强度减小，使火焰的一般特征几乎保持不变。两种火焰的温度和离子电流强度波动频谱表明，在最大激发强度下，只观察到300Hz的基频峰及其部分谐波，没有表现出任何白噪声特征。由此证明了声激励在湍流火焰的锁相平均测量中是非常有用的。得到了两种双火焰连续8个相的二维相平均温度和离子电流强度分布图，清晰地展示了从有组织涡流形成到涡流火焰形成的整个过程。结果表明，平面扩散火焰中有组织涡流火焰的平均寿命约为有组织涡流形成周期（1/300秒）的3倍，而尾流火焰中有组织涡流火焰的平均寿命约为有组织涡流形成周期（1/300秒）的2倍。少

Two types of dual diffusion flames established behind a rear-facing semicircular fuel nozzle were experimentally investigated ; one is the plane diffusion flame consisiting of an ordinary laminar diffusion flame on the lower-velocity side of the fuel nozzle and a lifted flame on the higher-velocity side, the other the bluffbody stabilized wake flame composed of two lifted flames on both sides of the fuel nozzle. The computer-aided phase-locked averaging method (the CAPLA method for short) was combined with the acoustic excitation to examine not only effects of the acoustic excitation on the flam estructure, but also phase characteristics of the formation processes of organized eddies and eddy-flames. The acoustic excitation was apploed by a flat loud-speaker flush-mounted on the higher-velocity side wall of the combustion tunnel at a constant frequency of 300Hz.According to flash shadowgraphs of flames the acoustic excitation was found to make the outline of eddy-flames clear with incr … More easing the excitation intensity due to rapid and clear formation of organized eddies, leaving general features of flames almost unvaried. Frequency spectra of fluctuating temperature and ion current intensity for two kinds of flames showed that, at the maximum excitation intensity applied, only the fundamental peak at 300Hz and some of its harmonics were observed without exhibiting any white noise character. Therefore, it was proved that the acoustic excitation is very usefulin the phase-locked-averaging measurements of turbulent flames.Two dimensional phase-averaged temperature and ion current intensity profiles at eight consecutive phases obtained for two kinds of dual flames demonstrated clearly the entire process from the formation of an organized eddy to the establishment of an eddy-flame. As a result, an organized eddy-flame in the plane diffusion flame was found to have an mean lifetime of about three times the period of organized eddy formation of 1/300 sec, while the lifetime of an organized eddy-flame in the wake flame was about twice the period of the organized eddy formation. Less