Active Control and Noise Reduction of Turbulent Diffusion Flames with Coherent Structure by Acoustic Excitation

在这项研究中，两种扩散火焰是在相同的几何和流动条件下，在相同的几何和流动条件下被声学激励的，它们建立在二维燃烧风洞中的后向半圆形圆柱体后面，具有剪切流动固有的相干结构。采用了两种激励技术：一种是平面扬声器方法，扬声器施加的声压波动直接刺激剪切层中的Kelvin-Helmholtz不稳定性，促进了一系列相干结构的形成；另一种是燃料供应速度波动方法，即在喷嘴上游的燃油供应管路上施加规定幅度的燃料流量波动。为了阐明声激励对燃烧特性的影响，测量了平均浓度分布和温度波动。此外，还尝试使用PIV技术来构造算法，即…通过钝体后面的回流区，更多地实现了速度矢量剖面的光学和平面测量。主要研究结果如下：(1)采用转镜法加上偏置速度，使得速度矢量方向的判别成为可能。基于各种观测和考虑，构造了PIV算法，该算法由模式识别、矢量计算、误差矢量消除和矢量内插四部分组成。结果表明，本文提出的PIV算法可以对具有反向流动的反应性湍流流场进行图像处理。(2)虽然两种激励技术都增强了拟序结构的周期性，但供油速度脉动法比平面扬声器方法更有效。(3)随着激励强度的增加，有序涡的尺度变得均匀，火焰区域集中在半圆形喷管后面的中心区域，火焰长度变短，表明促进了反应和燃烧强度。结果表明，在中心火焰区，NOx和CO_2增加，CO和HC减少，而在有组织涡焰区域，由于有组织涡的强烈吞没运动产生了严重的冷却效应，CO和HC减少。较少

In this investigation two types of diffusion flames, which are established behind a rear facing semi-circular cylinder in a 2-D combustion tunnel and are characterized by the coherent structure inherent in shear flows, are acoustically excited under the same geometrical and flow conditions. Two kinds of excitation techniques are used ; one is the flat speaker method, in which the sound pressure fluctuation applied by the speaker stimulates directly the Kelvin-Helmholtz instability in the shear layr and promotes the formation of a series of coherent structure, and the other is the fuel supply velocity fluctuation method, in which fluctuation having a prescribed amplitude of fuel flow rate is applied to the fuelflow supply line upstream of the nozzle. In order to elucidate effects of the acoustic excitation on the combustion characteristics, mean concentration profiles and temperature fluctuations are measured. Also an attempt is made to construct algorithm using the PIV-technique, that … More enables optical and planar measurements of the velocity vector profiles with a recirculation zone behind a bluffbody. The results obtained are summarized as follows.(1) addition of the bias-velocity using a rotating mirror method makes discrimination of the velocity vector direction possible. Based on various kinds of observations and considerations, the PIV-algorithm is constructed, which consists of the pattern discrimination, the vector calculation, the error vector elimination and the vector interpolation. It is shown that the proposed PIV-algorithm makes possible picture processing of the reactive turbulent flow field with reverse flows.(2) Although two types of excitation techniques equally enhance the periodicity of the coherent structure, the fuel supply velocity fluctuation method is found to be more effective than the flat speaker method.(3) With increasing the excitation intensity, the scale of organized eddies becomes uniform, the flame region is concentrated into the central zone behind the semicircular nozzle, and the flame length becomes short, indicating the promotion of reaction and combustion intensity. As a result, in the central flame region NOx and CO_2 increase, and CO and HC decrease, whereas in the organized eddy-flame region the very reverse holds, due to the severe cooling effect by the intense engulfing motion of the organized eddies. Less