Merging of corotating vortices is of primary interest in the field of supersonic mixing due to the ability of two or more structures to coalesce and form a larger one which enhances the stirring motion and straining in the flow, thus promoting turbulence production and mixing augmentation. During experimental efforts aimed at quantifying mean and fluctuating flowfields produced by the merging of two supersonic streamwise corotating vortices through stereoscopic particle image velocimetry, it was noticed that both the strain rates and turbulent kinetic energy would peak within the elongated merger’s vorticity patch. The article discusses how this is in fact a counterintuitive phenomenon and shows that a possible explanation can be given by studying the flow within a frame of reference which rotates with the merger itself. It will be shown how the merger is surrounded by a different flowfield than that measured in the laboratory frame of reference, characterized by the presence of recirculation zones referred to as ghost vortices. These vortices introduce large rates of strain within the merger, thus providing a possible justification for the high levels of turbulence attained within the rotating structure. The experimental findings are strongly corroborated by reduced-order, inviscid simulations, showing the formation of similar structures and clarifying the presence of peaks of strain rates within the merger.

由于两个或更多个结构的聚结和形成较大的结构的能力，共旋转涡旋的合并在超音速混合领域中是最重要的，这增强了搅拌运动和流动中的应变，从而促进了湍流的产生和混合的增加。在旨在通过立体粒子图像测速定量两个超声速沿流同向旋涡合并而产生的均值和波动流场的实验工作中，注意到应变率和湍动能都将在拉长的合并涡旋斑内达到峰值。本文讨论了这实际上是一种违反直觉的现象，并表明可以通过研究与合并本身一起旋转的参考框架内的流动来给出可能的解释。幽灵漩涡。这些涡流在合并过程中引入了很大的应变率，因此为旋转结构内获得的高水平湍流提供了可能的证明。实验结果得到了降阶，无粘性模拟的有力佐证，显示出相似结构的形成并澄清了合并中应变率峰值的存在。