Decay of Turbulence near the Local Reaction Zone of A Turbulence Premixed Flame

本文试图测量湍流预混火焰局部反应区内的Kolmogorov湍流标度，建立在无反应流动中的Kolmogorov湍流标度小于层流预混火焰厚度的区域。为了测量局部反应区内的Kolmogorov湍流标度，采用了由激光测速系统和微静电探头组成的特殊诊断装置。利用这种技术，可以成功地将局部反应区内的速度波动与未燃烧的混合物或燃烧的气流中的速度波动区分开来。由速度脉动得到的功率谱密度函数可以估算局部反应区湍流的Kolmogorov尺度，而由进流速度脉动得到的湍流功率谱密度函数、湍流强度和Kolmogorov尺度与非反应流中的一致。在非反应流动中存在小于层流预混火焰厚度的小尺度旋涡，研究发现，由于放热导致气体的膨胀，在局部反应区内存在较小尺度的旋涡。由局部反应区速度起伏引起的Kolmogorov湍流标度远大于层流预混火焰厚度。这一结果表明，进场流动中的小尺度涡流可能无法通过预热区。

An attempt has been made to measure the Kolmogorov scale of turbulence within the local reaction zone of a turbulent premixed flame established in a regime in which the Kolmogorov scale of turbulence in the non-reacting flow is smaller than the laminar premixed flame thickness. in order to measure the Kolmogorov scale of turbulence within the local reaction zone, the specially arranged diagnostics composed of the LDV system and the micro-electrostatic probe has been adopted. By using this technique, the velocity fluctuation within the local reaction zone can be successfully distinguished from that in unburned mixture or burned gas stream. Thus, the Kolmogorov scale of turbulence in the local reaction zone could be evaluated on the basis of the power spectrum density function derived from the velocity fluctuations.The powers spectrum density function, the turbulence intensity and the Kolmogorov scale of turbulence derived from velocity fluctuations in the approach flow are shown to be the same as those in the non-reacting flow. Also, the small scale eddies in the non-reacting flow, which are smaller than the laminar premixed flame thickness, are confirmed to exist in the approach flow.It is found that the approach flow turbulence increases in the local reaction zone because of the expansion of gases due to heat release. The Kolmogorov scale of turbulence derived from velocity fluctuations in the local reaction zone is shown to be much larger than the laminar premixed flame thickness. this result implies that the small scale eddies in the approach flow may not survive through the preheat zone.