The characteristics of square twin surface jets at various offset heights from the free surface were studied using a particle image velocimetry technique. The offset heights were varied from 1 to 4 nozzle widths at a fixed Reynolds number of 3890. The entrainment and mixing characteristics were examined using the potential core length, merging point, combined point, maximum velocity decay, half-velocity width and were found be nearly independent of offset height in near field. The jet–surface interaction was examined by surface velocity, vorticity thickness and surface turbulence intensities. The growth rate of the vorticity thickness reduced in the interaction region; and was more severe for shorter offset height. Turbulent structures were examined using weighted joint probability density function and two-point cross-correlations between swirling strength and velocity fluctuations. Weaker turbulent events were observed for deeper jet close to a free surface at the streamwise location beyond the attachment point.

中文翻译：

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偏移高度对双表面射流湍流特性的影响

使用粒子图像测速技术研究了距自由表面不同偏移高度的方形双表面射流的特性。在 3890 的固定雷诺数下，偏移高度从 1 到 4 个喷嘴宽度变化。使用潜在的核心长度、合并点、组合点、最大速度衰减、半速宽度检查夹带和混合特性，发现是几乎与近场中的偏移高度无关。通过表面速度、涡度厚度和表面湍流强度检查射流-表面相互作用。相互作用区涡度厚度的增长速度减小；并且对于较短的偏移高度更严重。使用加权联合概率密度函数和涡流强度和速度波动之间的两点互相关来检查湍流结构。对于在附着点以外的流向位置靠近自由表面的更深的射流，观察到较弱的湍流事件。