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首页> 外文期刊>Experimental Thermal and Fluid Science: International Journal of Experimental Heat Transfer, Thermodynamics, and Fluid Mechanics >Droplet clustering and local spray unsteadiness in air-assisted sprays
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Droplet clustering and local spray unsteadiness in air-assisted sprays

机译：液滴聚类和局部喷涂在空气辅助喷雾中的不稳定性

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摘要

The clustering of droplets in air-assisted water sprays operating under ambient atmospheric conditions is experimentally studied with the aim to characterize the droplet clusters and study the consequence of clustering on local turbulent mass flux of droplets. Planar measurements of droplet number density and velocity were achieved by application of the PIV technique, while the ILIDS technique was used for sizing individual droplets. Experiments were performed for four different injector operating conditions corresponding to different liquid mass fractions at the radial measurement stations far downstream of the injector exit. The droplet clusters were statistically characterized by the measurement of the D parameter. The clustering of droplets occurs over a range of length scales, however, the largest length scale of droplet clusters (L-c) was found to scale with large eddies of the turbulent air flow around droplets. For higher local liquid mass fraction, the D parameter was also higher, while L-c was smaller, indicating intense clustering. The local turbulent number flux of droplets, which is essentially the correlation between fluctuations of the droplet number density and the droplet velocity ((nu) over bar), was found to be non-negligible relative to the steady flux especially towards the edge of the spray, where the tendency of the droplets for clustering was found to be higher. Also, the correlation (nu) over bar was always negative suggesting that locally higher droplet number density due to passage of the clusters of droplets leads to smaller droplet velocity fluctuations.
机译：通过实验研究了在环境大气条件下运行的空气辅助水喷雾中的液滴的聚类，目的是表征液滴簇，并研究聚类对局部湍流质量磁通量的结果。通过应用PIV技术实现了液滴数密度和速度的平面测量，而ILIDS技术用于尺寸尺寸的单个液滴。对对应于在喷射器出口下游的径向测量站的不同液体质量级分的四种不同的注射器操作条件进行实验。通过测量D参数，液滴簇的特征在于。液滴的聚类发生在一系列长度范围内，然而，发现液滴簇（L-C）的最大长度尺度与液滴周围的湍流空气流的大漩涡缩放。对于较高的局部液体质量分数，D参数也较高，而L-C较小，表示强烈的聚类。液滴的局部湍流数量，这基本上是液滴数密度的波动与液滴速度（（nu）上方的液滴）之间的相关性，而不是稳定的助焊剂是不可忽略的，尤其是朝向边缘喷雾，发现液滴用于聚类的趋势更高。此外，上方的相关性（Nu）始终是负面的，表明由于液滴簇通过导致的局部液滴数密度导致较小的液滴速度波动。

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