The momentum transport and entrainment of a developing plane jet are dominated by coherent structures. Percipience about the formation, evolution, and interaction of these coherent structures for oscillating planar jets remains unclear. In the present study, numerical investigations are reported for analyzing spatially oscillating planar jets by solving Navier–Stokes equations coupled with the volume of fluid method to track the air–water interface. Coherent structures in the flow for Reynolds numbers (Re) 4500 and 500 are identified using Q-criterion. It is demonstrated that for oscillating jets, the spread and entrainment increase with an increase in Re. These jet characteristics are greatly influenced by the head vortices, which transform into a pair of hairpin vortices, which further undergo leapfrogging. This jet front dynamics is found to be dampened by viscous forces. The numerical results also suggest the existence of sideways hairpin vortices that expel the fluid by forming a channel and are significantly subdued at low Re. A peculiar merging of span-wise Kelvin–Helmholtz rollers at low Re is also reported in the present study. Furthermore, the dominant flow structures are identified and analyzed using proper orthogonal decomposition and dynamic mode decomposition. The results demonstrate the dominance of coherent structures at the downstream for higher Re with vortices in the near field at the jet peaks also contributing to the flow field dynamics.

中文翻译：

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在静止大气中发展的空间振荡平面液体射流的相干结构

发展中的飞机喷流的动量传输和夹带由相干结构主导。关于振荡平面射流的这些相干结构的形成、演化和相互作用的认识仍不清楚。在本研究中，通过求解 Navier-Stokes 方程结合流体体积法来跟踪空气-水界面，对空间振荡平面射流进行了数值研究。雷诺数 (Re) 4500 和 500 的流动中的相干结构使用 Q 标准进行识别。结果表明，对于振荡射流，扩散和夹带随 Re 的增加而增加。这些射流特性受头涡影响很大，头涡转变为一对发夹涡，进一步进行越级。发现这种射流前沿动力学受到粘性力的抑制。数值结果还表明存在侧向发夹涡流，该涡流通过形成通道来排出流体，并且在低 Re 时被显着抑制。本研究还报道了在低 Re 下展向开尔文-亥姆霍兹滚子的特殊合并。此外，使用适当的正交分解和动态模式分解来识别和分析主要流动结构。结果表明，下游的相干结构占主导地位，具有较高的 Re，喷射峰处的近场涡流也有助于流场动力学。本研究还报道了在低 Re 下展向开尔文-亥姆霍兹滚子的特殊合并。此外，使用适当的正交分解和动态模式分解来识别和分析主要流动结构。结果表明，下游的相干结构占主导地位，具有较高的 Re，喷射峰处的近场涡流也有助于流场动力学。本研究还报道了在低 Re 下展向开尔文-亥姆霍兹滚子的特殊合并。此外，使用适当的正交分解和动态模式分解来识别和分析主要流动结构。结果表明，下游的相干结构占主导地位，具有较高的 Re，喷射峰处的近场涡流也有助于流场动力学。