Study of Spectral Noise Emissions from Standard Turbulent Nonpremixed Flames
Study of Spectral Noise Emissions from Standard Turbulent Nonpremixed Flames
复制标题
标准湍流非预混火焰的频谱噪声发射研究
作者：
Kapil Singh;S. Frankel;J. Gore
振荡燃烧和燃烧不稳定性的发生引起了人们对火焰噪声的原因、机制、抑制和控制的兴趣。非预混合火焰噪声频率较低，并且难以使用传统的声学衬里进行控制，因此需要通过改变源来显着降低噪声。封闭火焰产生的噪声具有更大的实际意义，但比明火产生的噪声更复杂，而明火本身尚不清楚。通过研究火焰声音的频谱内容，试图加深对明火产生的噪声的理解，文献中提供了详细的速度、标量特性和辐射测量（国际湍流非预混研讨会火焰；http://www.ca.sandia.gov/TNF/abstract.html）。与相同雷诺数下空气射流产生的声音的频谱内容进行了比较。在所有频率下，火焰产生的频谱声压级（SSPL）均高于相应空气射流产生的频谱声压级。 SSPL 之间的差异在 400-2000 Hz 的相对低频范围内最大。对于靠近轴的位置，火焰在此频率范围内发出恒定的 SSPL。该范围的宽度在较大的径向位置处减小。频率越高，流速的影响越强。频谱显示远离燃烧器出口的高频分量显着减少，特别是在轴向方向。这些观察结果可用于设计噪声较低的燃烧器，也可用于评估计算气动声学代码。
The occurrence of oscillating combustion and combustion instability has led to resurgence of interest in causes, mechanisms, suppression, and control of flame noise. Nonpremixed flame noise is low frequency and difficult to control using conventional acoustic liner and so significant noise reduction needs to be achieved by altering the source. Noise generated by enclosed flames is of greater practical interest but is more complicated than the noise generated by open flames, which itself is not clearly understood. Improved understanding of the noise generated by open flames is attempted by studying spectral content of the sound for flames for which detailed velocity, scalar property, and radiation measurements are available in the literature (International Turbulent Non-Premixed Workshop flames; http://www.ca.sandia.gov/TNF/abstract.html). Comparisons were made with the spectral content of sound generated by air jets at identical Reynolds numbers. The spectral sound pressure levels (SSPL) generated by the flames were higher than those generated by corresponding air jets at all frequencies. The differences between the SSPL were the highest in the relatively low-frequency range of 400-2000 Hz. The flames emanate a constant SSPL in this frequency range for locations near the axis. The width of this range decreases at larger radial locations. The effects of flow velocity are stronger at higher frequencies. The spectra show substantial reduction in highfrequency components away from the burner exit, especially in the axial direction. These observations can be used for designing combustors with lower noise and also in the evaluation of computational aeroacoustics codes.