Transverse jet mixing characteristics
Transverse jet mixing characteristics
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横向喷射混合特性
DOI：
10.1017/jfm.2016.5
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发表时间：
2016
影响因子：
3.7
通讯作者：
A. Karagozian
中科院分区：
文献类型：
--
作者：
L. Gevorkyan;T. Shoji;D. Getsinger;Owen Smith;A. Karagozian
该实验研究探索并量化了在一系列流动和注射条件下垂直注入交叉流的气体圆形射流相关的混合特性。该研究利用丙酮平面激光诱导荧光成像来确定射流中心面和横截面的混合指标，包括一系列射流与横流动量通量比 ( $2\leqslant J\leqslant 41$ )、密度比 ( $0.35\leqslant S\leqslant 1.0$ ) 和喷射器配置（冲洗喷嘴、冲洗管道和高架喷嘴），所有这些均在固定射流处进行雷诺数为 1900。对于所探索的大多数条件，射流上游剪切层不稳定性的性质与结构之间存在直接对应关系，如 Getsinger 等人中详细记录的那样。 (J. Fluid Mech., vol. 760, 2014, pp. 342–367)，以及射流的混合特性，与扩散主导的过程一致，但有一些值得注意的例外。当量化为沿射流轨迹的距离的函数时，具有绝对不稳定的上游剪切层和相对对称的反向旋转涡对横截面结构的交叉流中的射流的混合度量往往比具有对流不稳定的上游剪切层和通常不对称的横截面结构的射流表现出更好的局部分子混合。然而，对于一些特定的对流不稳定条件，下游距离的混合空间演变可能更大，这显然与作为改善混合的触发因素的剪切层卷起的启动和性质有关。这些趋势的一个值得注意的例外是，横流中的等密度射流具有已经绝对不稳定的上游剪切层，并且与横流相比，射流密度降低。在这里，低于统一的密度比往往比等密度条件混合得不好，这被证明是由于较高密度横流夹带进入较低密度剪切层涡流的性质差异造成的。
This experimental study explores and quantifies mixing characteristics associated with a gaseous round jet injected perpendicularly into cross-flow for a range of flow and injection conditions. The study utilizes acetone planar laser-induced fluorescence imaging to determine mixing metrics in both centreplane and cross-sectional planes of the jet, for a range of jet-to-cross-flow momentum flux ratios ( $2\leqslant J\leqslant 41$ ), density ratios ( $0.35\leqslant S\leqslant 1.0$ ) and injector configurations (flush nozzle, flush pipe and elevated nozzle), all at a fixed jet Reynolds number of 1900. For the majority of conditions explored, there is a direct correspondence between the nature of the jet’s upstream shear layer instabilities and structure, as documented in detail in Getsinger et al. (J. Fluid Mech., vol. 760, 2014, pp. 342–367), and the jet’s mixing characteristics, consistent with diffusion-dominated processes, but with a few notable exceptions. When quantified as a function of distance along the jet trajectory, mixing metrics for jets in cross-flow with an absolutely unstable upstream shear layer and relatively symmetric counter-rotating vortex pair cross-sectional structure tend to show better local molecular mixing than for jets with convectively unstable upstream shear layers and generally asymmetric cross-sectional structures. Yet the spatial evolution of mixing with downstream distance can be greater for a few specific convectively unstable conditions, apparently associated with the initiation and nature of shear layer rollup as a trigger for improved mixing. A notable exception to these trends concerns conditions where the equidensity jet in cross-flow has an upstream shear layer that is already absolutely unstable, and the jet density is then reduced in comparison with that of the cross-flow. Here, density ratios below unity tend to mix less well than for equidensity conditions, demonstrated to result from differences in the nature of higher-density cross-flow entrainment into lower-density shear layer vortices.