Investigation of the near field dynamics of a single and tandem array of three jets are provided by 2-D time-resolved particle image velocimetry (TR-PIV) measurements. Instantaneous velocity fields are examined in the transverse and spanwise planes with jet to crossflow velocity ratios in the range from 0.9 to 1.7. Previous studies have shown that for high ratios (\(\ge\) 2), the leading jet provides sufficient shielding to ensure that all jets downstream exhibit nearly identical flow characteristics. The current transverse plane measurements exhibit more unique and localized features as a result of the competing effects of pressure gradients and vortex mechanisms assessed via the jet exit profiles, first and second order turbulent statistics, streamline trajectories, recirculation areas and penetrations depths. Proper orthogonal decomposition (POD) is applied to the spanwise plane instantaneous velocity fields to determine the statistically dominant features of the single and tandem jet configurations at equivalent velocity ratios. The velocity fields are then reconstructed using the truncated POD modes to provide further insight into the shear layer and wake vortices that drive these configurations. Vortex identification algorithms are applied to the reconstructed velocity fields to determine the statistical characteristics of the vortices, including their centroids, populations, areas and strengths, each of which exhibit largely different dependencies on jet configuration and velocity ratio. Several of the investigated metrics are found to exhibit different behaviors below and above a velocity ratio of unity and also as a function of increasing velocity ratio between 1 and 2, implying that several transitions mechanisms are present in the low velocity ratio regime investigated herein.

Graphic abstract

中文翻译：

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在低速比下错流中串联射流阵列的时间分辨粒子图像测速仪测量

通过二维时间分辨粒子图像测速（TR-PIV）测量，可以对三个喷嘴的单个串联阵列的近场动力学进行研究。在横断面和翼展方向上检查瞬时速度场，射流与横流的速度比在0.9到1.7的范围内。先前的研究表明，对于高比率（\（\ ge \）2），前导射流提供足够的屏蔽，以确保下游的所有射流都表现出几乎相同的流动特性。由于通过射流出口剖面，一阶和二阶湍流统计，流线轨迹，再循环面积和穿透深度评估的压力梯度和涡旋机制的竞争效应，当前的横断面测量结果显示出更多独特和局部的特征。将适当的正交分解（POD）应用于翼展方向平面瞬时速度场，以确定在等效速度比下单喷射和串联喷射构型的统计主导特征。然后，使用截断的POD模式重建速度场，以提供对剪切层和驱动这些配置的尾流涡流的进一步了解。将涡流识别算法应用于重建的速度场，以确定涡流的统计特征，包括其质心，总体，面积和强度，每个特征对射流配置和速度比的依赖性都很大。发现一些调查的指标在统一的速度比之下和之上表现出不同的行为，并且还表现为速度比在1和2之间的增加，这意味着本文研究的低速比率方案中存在几种过渡机制。每一个都表现出对射流配置和速度比的很大不同的依赖关系。发现一些调查的指标在统一的速度比之下和之上表现出不同的行为，并且还表现为速度比在1和2之间的增加，这意味着本文研究的低速比率方案中存在几种过渡机制。每一个都表现出对射流配置和速度比的很大不同的依赖关系。发现一些调查的指标在统一的速度比之下和之上表现出不同的行为，并且还表现为速度比在1和2之间增加的函数，这意味着本文研究的低速比率方案中存在几种过渡机制。

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