Instabilities in the wake of an inclined prolate spheroid

TL;DR

This study uses direct numerical simulations to explore the complex flow instabilities, bifurcations, and wake transitions behind an inclined prolate spheroid across a broad range of Reynolds numbers, revealing new flow features.

Contribution

It provides a detailed analysis of wake instabilities and flow features behind an inclined prolate spheroid, including the discovery of a helical vortex structure and symmetry alterations.

Findings

Symmetry loss and unsteadiness increase with Reynolds number.

Identification of a helical vortex tube in the wake.

Observation of self-similarity in the far wake.

Abstract

We investigate the instabilities, bifurcations and transition in the wake behind a 45-degree inclined 6:1 prolate spheroid, through a series of direct numerical simulations (DNS) over a wide range of Reynolds numbers (Re) from 10 to 3000. We provide a detailed picture of how the originally symmetric and steady laminar wake at low Re gradually looses its symmetry and turns unsteady as Re is gradually increased. Several fascinating flow features have first been revealed and subsequently analysed, e.g. an asymmetric time-averaged flow field, a surprisingly strong side force etc. As the wake partially becomes turbulent, we investigate a dominating coherent wake structure, namely a helical vortex tube, inside of which a helical symmetry alteration scenario was recovered in the intermediate wake, together with self-similarity in the far wake.