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Material spike formation in highly unsteady separated flows. (English) Zbl 1430.76280

Summary: We apply the recent frame-invariant theory of separation spike formation to complex unsteady flows, including a turbulent separation bubble, an impinging jet, and flows around a freely moving cylinder and a freely rotating ellipse. We show how the theory captures the onset of material spike formation, without any assumption on the flow type (steady, periodic, unsteady) or separation type (on- or off-wall, fixed or moving boundaries). We uncover new phenomena, such as the transition from on-wall to off-wall separation, the merger of initially distinct spikes, and the presence of severe material spikes that remain hidden to previous approaches. Remarkably, even in steady flows around curved boundaries, we detect material spikes in the absence of flow reversal, the main ingredient to existing separation criteria. Together, our results unveil how an involved network of spikes arises, interacts and merges dynamically, leading to the final ejection of particles from the wall in highly transient flow separation processes.

MSC:

76F40 Turbulent boundary layers
76F65 Direct numerical and large eddy simulation of turbulence
37N10 Dynamical systems in fluid mechanics, oceanography and meteorology

Software:

FreeFem++
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Full Text: DOI arXiv

References:

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