Material spike formation in high Reynolds number flow separation

TL;DR

This paper applies a frame-invariant theory to complex unsteady flows to accurately identify the onset and evolution of material spike formation during flow separation, revealing new phenomena and dynamic interactions.

Contribution

It demonstrates the theory's ability to capture spike formation in diverse unsteady flows without assumptions on flow or separation type, uncovering new dynamic phenomena.

Findings

Identifies transition from on-wall to off-wall separation.

Reveals merger of initially distinct spikes.

Shows severe spikes hidden to previous methods.

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. These 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.