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ANALYSIS OF ACOUSTIC WAVE INTERACTIONS WITH TURBULENT PREMIXED FLAMES

机译:湍流预混火焰声波相互作用的分析

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This paper analyzes acoustic wave interactions with turbulent, premixed flames. It generalizes a previous study that treated the flame as a passive temperature discontinuity by accounting for the effects of pressure disturbances upon the mass burning rate. Similar to the prior study the problem is posed with an integral formulation of the wave equation and assumes that the local flame front curvature is much larger than the acoustic wavelength. Thus, it is most appropriate for considering interactions between flames and short-wavelength (e.g., high-frequency) disturbances. The analysis includes such factors as the response of the mass burning rate to acoustic perturbations, the temperature change across the flame, and the geometric complexities of the evolving, wrinkled front. Explicit solutions are derived for the coherent field, showing that its characteristics are controlled by the wavelength of the disturbance, the probability density function of the flame front position and orientation, the incident wave angle, the temperature jump across the flame, and the response of the mass burning rate to acoustic perturbations. These results suggest that several differences exist between the characteristics of waves scattered from laminar and turbulent flames. With increased flame front wrinkling, the coherent field becomes increasingly independent of the temperature jump across the flame and response of the mass burning rate. This result contrasts with the strong importance of these parameters in laminar-flame-acoustic-wave interaction problems. In addition, results show that the wrinkled characteristics of turbulent flames shift the phase and reduce the amplitude of the coherent field relative to its value if the flame front were smooth; that is, they serve as a source of damping of coherent acoustic energy. This damping source is particularly significant for disturbances whose wavelengths are on the order of or smaller than the characteristic scales of flame wrinkling.
机译:本文分析了湍流,预混火焰与声波的相互作用。它概括了以前的研究,该研究通过考虑压力扰动对整体燃烧速率的影响,将火焰视为被动的温度不连续性。与先前的研究类似,该问题由波动方程的积分公式提出,并假设局部火焰前曲率比声波波长大得多。因此,最适合考虑火焰与短波(例如,高频)干扰之间的相互作用。分析包括诸如质量燃烧速率对声学扰动的响应,火焰上的温度变化以及不断发展的,起皱的前部的几何复杂性等因素。导出了相干场的显式解,表明其特性受扰动波长,火焰前沿位置和方向的概率密度函数,入射波角,火焰温度跃迁以及火焰响应的控制。质量燃烧速率对声学扰动的影响。这些结果表明,层流和湍流火焰散射的波的特性之间存在若干差异。随着火焰前褶皱的增加,相干场变得越来越独立于火焰上的温度跃变和整体燃烧速率的响应。该结果与这些参数在层流-火焰-声波相互作用问题中的重要意义形成鲜明对比。另外,结果表明,如果火焰前缘是光滑的,湍流火焰的起皱特性会改变相位,并减小相干场的振幅(相对于其值)。也就是说,它们充当了相干声能的阻尼源。对于波长约为或小于起皱纹特征尺度的干扰,此阻尼源特别重要。

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