We present a new technique to study preferential concentration of droplets in a turbulent air flow. Preferential concentration is the tendency of droplets to cluster in regions of strain, while avoiding regions of rotation. We study the properties of the droplet concentration field in zero mean flow turbulence that was created using an array of synthetic jets. The droplets are made of a phosphorescent solution of Europium chelate. They are excited by a laser sheet from a pulsed UV laser, after which the glowing droplets are followed using a high-speed intensified camera. % We quantify preferential concentration through measurement of the density–density correlation function and the fractal dimension of the droplet distribution. We argue that this correlation function is similar to the two-dimensional projection of the well-known radial distribution function. At the Stokes numbers studied (${\rm St}\approx 2$) we find strong clustering, as quantified by a large value of the clustering exponent.

中文翻译：

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使液滴在湍流中发光

我们提出一种新技术来研究湍流中液滴的优先浓度。优先浓度是液滴在应变区域内聚集的趋势，同时避免了旋转区域。我们研究了使用合成射流阵列创建的零均流湍流中液滴浓度场的特性。液滴由Euro螯合物的磷光溶液制成。它们由脉冲紫外激光的激光片激发，然后使用高速增强相机跟踪发光的液滴。％我们通过测量密度-密度相关函数和液滴分布的分形维数来量化优先浓度。我们认为，该相关函数类似于众所周知的径向分布函数的二维投影。在斯托克斯学习的数字（$ {\ rm St} \ approx 2 $），我们发现强大的聚类，可以通过较大的聚类指数值来量化。