Abstract Understanding the near-field region of a spray is integral to optimization and control efforts because this region is where liquid break-up and spray formation occurs, setting the conditions under which the spray dynamics evolve under the gas turbulence and droplet inertia. However, the high optical density of this region complicates measurements; thus, it is not yet well characterized. This paper is intended to compare four of the leading experimental techniques that are being used or developed to study the near-field region of a spray. These techniques are shadowgraphy, tube source X-ray radiography, high-speed synchrotron white-beam X-ray imaging, and synchrotron focused-beam X-ray radiography. Each of these methods is applied to a canonical spray, using the same nozzle, under identical flow conditions. Synchrotron focused-beam radiography shows that a time-averaged Gaussian liquid distribution is a valid approximation very near the nozzle, before the core has broken apart. The Gaussian behavior continues as the spray progresses further downstream, showing self-similarity. A spray angle can be defined from the linear spreading of the Gaussian intensity distribution with downstream distance. The spray angle found from shadowgraphy is validated with focused-beam testing. Additionally, a novel method of estimating the intact length of the spray from different X-ray techniques, that uses broadband illumination, is presented.

中文翻译：

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光密同轴空气辅助雾化器近场 X 射线和光学测量的比较

摘要 了解喷雾的近场区域是优化和控制工作不可或缺的一部分，因为该区域是发生液体分解和喷雾形成的地方，设定了在气体湍流和液滴惯性下喷雾动力学发展的条件。然而，该区域的高光密度使测量复杂化。因此，它还没有很好地表征。本文旨在比较四种主要的实验技术，这些技术正在使用或开发来研究喷雾的近场区域。这些技术是阴影照相术、管源 X 射线照相术、高速同步加速器白束 X 射线成像和同步加速器聚焦束 X 射线照相术。这些方法中的每一种都适用于标准喷雾，使用相同的喷嘴，在相同的流动条件下。同步加速器聚焦束射线照相显示，在核心破裂之前，时间平均的高斯液体分布是非常靠近喷嘴的有效近似值。随着喷雾进一步向下游推进，高斯行为继续，表现出自相似性。喷射角可以由高斯强度分布随下游距离的线性扩展来定义。从阴影成像中发现的喷射角度通过聚焦光束测试进行验证。此外，还介绍了一种使用宽带照明估计来自不同 X 射线技术的喷雾完整长度的新方法。表现出自相似性。喷射角可以由高斯强度分布随下游距离的线性扩展来定义。从阴影成像中发现的喷射角度通过聚焦光束测试进行验证。此外，还介绍了一种使用宽带照明估计来自不同 X 射线技术的喷雾完整长度的新方法。表现出自相似性。喷射角可以由高斯强度分布随下游距离的线性扩展来定义。从阴影成像中发现的喷射角度通过聚焦光束测试进行验证。此外，还介绍了一种使用宽带照明估计来自不同 X 射线技术的喷雾完整长度的新方法。