The jet in crossflow, or a transverse jet, eventually undergoes a linear transition from convectively to absolutely/globally unstable as the crossflow to jet velocity ratio increases. This flow field, however, has an extremely complex dynamics. Hence, determining this transition location is not a trivial task. It has long been known that this transition is associated with the upstream shear layer connected to the near field Kelvin-Helmholtz vortex ring, but it was only recently that the most unstable global mode and wave maker were located there as well. These findings led to the realization that an inviscid and planar linear stability analysis of the local velocity profile extracted from the jet in the crossflow upstream shear layer was strongly correlated with its transition to absolute/global instability. It is shown in this paper that such an analysis can be turned into an accurate predictive tool with the use of a viscous (instead of inviscid) and round (instead of planar) mixing layer. In other words, replacing an inviscid analysis of a planar mixing layer with counterflow by a viscous analysis of a round coaxial jet with outer nozzle suction leads to an accurate prediction of the jet in crossflow convective to an absolute instability transition.

中文翻译：

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射流在对流中从线性对流到绝对不稳定的线性转换的标准：逆流粘性和圆形混合层的类比

随着横流与射流速度比的增加，横流射流或横向射流最终经历了从对流到绝对/全局不稳定的线性过渡。然而，该流场具有极其复杂的动力学。因此，确定此过渡位置并不是一件容易的事。早已知道，这种过渡与连接到近场开尔文-亥姆霍兹涡旋环的上游剪切层有关，但是直到最近，最不稳定的全局模式和造波器也位于那里。这些发现导致人们认识到，从错流上游剪切层中的射流中提取的局部速度分布图的无粘性和平面线性稳定性分析与其向绝对/全局不稳定性的过渡密切相关。本文表明，通过使用粘性（而不是无粘性）和圆形（而不是平面）混合层，可以将这种分析转变为准确的预测工具。换句话说，用带有外部喷嘴吸力的圆形同轴射流的粘性分析来代替平面混合层的无粘性分析，从而可以准确预测横流中对流的射流，从而达到绝对不稳定的过渡。