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Material spike formation in highly unsteady separated flows

Published online by Cambridge University Press:  26 November 2019

Mattia Serra
Affiliation:
School of Engineering and Applied Sciences, Harvard University, Cambridge, MA02138, USA
Seán Crouzat
Affiliation:
Department of Mechanical Engineering, LADYF, Polytechnique Montréal, Montréal, QC,H3C 3A7, Canada
Gaël Simon
Affiliation:
Department of Mechanical Engineering, LADYF, Polytechnique Montréal, Montréal, QC,H3C 3A7, Canada
Jérôme Vétel
Affiliation:
Department of Mechanical Engineering, LADYF, Polytechnique Montréal, Montréal, QC,H3C 3A7, Canada
George Haller
Affiliation:
Institute for Mechanical Systems, ETH Zürich, Leonhardstrasse 21, 8092Zürich, Switzerland
Corresponding
E-mail address:

Abstract

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.

Type
JFM Papers
Copyright
© 2019 Cambridge University Press

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Serra et al. supplementary movie 1

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