Preferential concentration of poly-dispersed droplets in stationary isotropic turbulence
Preferential concentration of poly-dispersed droplets in stationary isotropic turbulence
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DOI：
10.1007/s00348-013-1525-3
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发表时间：
2013-05
影响因子：
2.4
通讯作者：
H. Lian;G. Charalampous;Y. Hardalupas
中科院分区：
文献类型：
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作者：
H. Lian;G. Charalampous;Y. Hardalupas
实验研究了Sauter平均直径在25 ~ 95 μm范围内的多分散水滴在四种不同湍流强度（Re λ= 107、145、185和213）的稳态均匀各向同性湍流中的优先浓度。描述了记录的来自液滴的散射光强度图像的图像处理方法，并且根据图像质量评估了其识别液滴的能力。评价了图像处理参数对测量的液滴聚类特性的影响。径向分布函数（RDF）和二维Voronoprano分析定量的大小的优先液滴浓度和两种方法的结果一致。RDF表明，在所有的实验条件下，所产生的液滴簇的特征长度尺度在20和30倍之间变化的Kolmogorov长度尺度。已经发现，优选浓度更适当地由斯托克斯数描述，基于各种代表性直径，即算术平均直径D10或直径DN 60%，低于该直径时喷雾中存在60%的总液滴数，或直径DV 5%，其携带喷雾中5%的总液体体积。在所有实验条件下，当所提出的Stokes数为1时，液滴优先浓度的大小最大。与最近的DNS研究结果相反，发现优先浓度的大小对湍流雷诺数的依赖性很小（Tagawa等人，J Fluid Mech 693：201-215，2012）。
The preferential concentration of poly-dispersed water droplets with a range of Sauter mean diameters between 25 and 95 μm has been studied experimentally in stationary homogeneous isotropic turbulence with four different intensities, characterized by turbulent Reynolds numbers based on Taylor microscale, ofReλ= 107, 145, 185 and 213. The image processing method of recorded scattered light intensity images from droplets is described and its ability to identify droplets is assessed in terms of image quality. The influence of image processing parameters on measured characteristics of droplet clustering is evaluated. The radial distribution function (RDF) and 2D Voronoï analysis quantified the magnitude of preferential droplet concentration and the results from both methods agreed well. RDF showed that the characteristic length scale of resulting droplet clusters varies between 20 and 30 times the Kolmogorov length scale over all the experimental conditions. It was found that the preferential concentration is more appropriately described by a Stokes number, based on various representative diameters, namely the arithmetic mean diameter,D10, or the diameter, DN60 %, below which 60 % of the total droplet number in the spray is present, or the diameter, DV5 %, which carries 5 % of the total liquid volume in the spray. The magnitude of droplet preferential concentration was maximum when the proposed Stokes number was around unity for all experimental conditions. Little dependence of the magnitude of preferential concentration on turbulent Reynolds numbers was found, in contrast to the recent DNS findings (Tagawa et al. in J Fluid Mech 693:201–215, 2012).