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

对后置半圆形燃油喷嘴后的两种双扩散火焰进行了实验研究，一种是由喷嘴低速侧的普通层流扩散火焰和较高速侧的提升火焰组成的平面扩散火焰，另一种是喷嘴两侧由两个提升火焰组成的钝体稳定尾迹火焰。将计算机辅助锁相平均法(简称CAPLA法)与声激励相结合，不仅考察了声激励对火焰结构的影响，而且研究了有序涡和涡焰形成过程的相位特征。声激励采用固定频率为300 Hz的平板式扬声器，安装在燃烧风洞的高速侧壁上。根据火焰的闪光阴影图，利用INCR…发现声激励使涡流火焰的轮廓清晰由于快速而清晰地形成有组织的涡流，激发强度更加缓和，使火焰的总体特征几乎保持不变。两种火焰的脉动温度和离子电流强度的频谱表明，在最大激发强度下，只观察到300 Hz的基波及其部分谐波，没有表现出任何白噪声特征。实验结果表明，声激励在湍流火焰的锁相平均测量中是非常有用的。获得了两种双火焰连续八个相的二维相平均温度和离子流强度分布，清楚地展示了从有组织涡流的形成到涡流火焰的建立的全过程。结果发现，平面扩散火焰中的有组织涡焰的平均寿命约为1/300秒有组织涡流形成周期的三倍，而尾迹火焰中有组织涡焰的平均寿命约为有组织涡流形成周期的两倍。较少

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