Abstract The fluid dynamics in the far-field of liquid sprays involves a wide range of spatio-temporal scales; challenging experimental observation and numerical modeling alike. Here we show how a combination of multiple imaging approaches, targeted to different scales, can provide useful insight into this class of flows. We performed multi-scale imaging measurements in the far-field of an upward-facing liquid spray issued into a large quiescent air chamber by a hollow-cone atomizer. Time-resolved planar laser imaging was carried out simultaneously over two nested windows: one aimed at the large-scale dynamics of the spray cone, and the other focused on the intermediate-scale motions spanning the cone half-width. Spray velocity fields were obtained from both windows via Particle Image Velocimetry (PIV) using robust phase correlation and multi-frame pyramid correlation. Additionally, Lagrangian droplet trajectories were obtained in the intermediate-scale window via Particle Tracking Velocimetry (PTV). Finally, droplet sizes and velocities were obtained via shadowgraphy using a double-pulsed LED source over a small-scale (cm-sized) window. We discuss the agreement between the different techniques, as well as the physical insight offered by the combined measurement approaches on various aspects of the flow, including: velocity self-similarity, correlated and uncorrelated motion, frequency content, and droplet size-velocity correlation.

中文翻译：

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远场区域向上液体喷雾的多尺度成像

摘要 液体喷雾远场流体动力学涉及广泛的时空尺度；具有挑战性的实验观察和数值建模。在这里，我们展示了针对不同尺度的多种成像方法的组合如何可以提供对此类流的有用见解。我们在由空心锥形雾化器喷入大型静止气室的朝上液体喷雾的远场中进行了多尺度成像测量。时间分辨平面激光成像在两个嵌套窗口上同时进行：一个针对喷雾锥的大尺度动力学，另一个针对跨越锥半宽度的中间尺度运动。使用稳健的相位相关和多帧金字塔相关，通过粒子图像测速 (PIV) 从两个窗口获得喷雾速度场。此外，拉格朗日液滴轨迹是通过粒子跟踪测速 (PTV) 在中间尺度窗口中获得的。最后，使用双脉冲 LED 光源在小尺度（厘米大小）窗口上通过阴影成像获得液滴尺寸和速度。我们讨论了不同技术之间的一致性，以及组合测量方法在流动的各个方面提供的物理洞察力，包括：速度自相似性、相关和不相关运动、频率内容和液滴尺寸-速度相关性。拉格朗日液滴轨迹是通过粒子跟踪测速 (PTV) 在中尺度窗口中获得的。最后，使用双脉冲 LED 光源在小尺度（厘米大小）窗口上通过阴影成像获得液滴尺寸和速度。我们讨论了不同技术之间的一致性，以及组合测量方法在流动的各个方面提供的物理洞察力，包括：速度自相似性、相关和不相关运动、频率内容和液滴尺寸-速度相关性。拉格朗日液滴轨迹是通过粒子跟踪测速 (PTV) 在中尺度窗口中获得的。最后，使用双脉冲 LED 光源在小尺度（厘米大小）窗口上通过阴影成像获得液滴尺寸和速度。我们讨论了不同技术之间的一致性，以及组合测量方法在流动的各个方面提供的物理洞察力，包括：速度自相似性、相关和不相关运动、频率内容和液滴尺寸-速度相关性。