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

本文研究了在相同的几何和流动条件下，建立在二维燃烧通道中后半圆柱体后的两种扩散火焰，它们具有剪切流固有的相干结构。采用了两种激励技术；一种是平面扬声器法，扬声器施加的声压波动直接刺激剪切层的开尔文-亥姆霍兹不稳定性，促进一系列相干结构的形成；另一种是供油速度波动法，在喷嘴上游的燃料流供应线上施加具有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，本文还尝试利用piv技术构建了一种算法，使其能够对崖体后再循环带的速度矢量剖面进行光学和平面测量。所得结果总结如下：(1)利用旋转镜法加入偏速，使速度矢量方向判别成为可能。基于各种观测和考虑，构建了piv算法，该算法包括模式识别、矢量计算、误差矢量消除和矢量插值。结果表明，所提出的piv算法使具有反向流动的反应性湍流场的图像处理成为可能。(2)虽然两种激励方法都能提高相干结构的周期性，但供油速度波动法比扁平扬声器法更有效。(3)随着激发强度的增加，有组织涡流的规模变得均匀，火焰区域集中到半圆形喷嘴后的中心区域，火焰长度变短，表明反应和燃烧强度得到了提高。结果，在火焰中心区域，NOx和CO_2增加，CO和HC减少，而在有组织涡流-火焰区域，由于有组织涡流的强烈吞没运动产生了严重的冷却作用，情况正好相反。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