Journal of Applied Mechanical Engineering

Bi-stability in turbulent wakes past 3D bluff bodies

2^nd International Conference on Fluid Dynamics & Aerodynamics

October 19-20, 2017 | Rome, Italy

Luc R Pastur and France Olivier Cadot

ENSTA ParisTech, France
University of Liverpool, UK

Posters & Accepted Abstracts: J Appl Mech Eng

Abstract:

Recent studies have shown that beyond some critical value of the ground clearance and Reynolds number, turbulent wakes past bluff bodies may undergo antisymmetric instabilities that result into the (steady) defelection of the wake in the direction of the body main shape ratio. As a consequence, additional lateral forces apply to the body, and temporally intermittent shifts from one deflected position to the symmetrical position are most usually observed. This resulting pitchfork bifurcation can be imperfect, when the yaw angle is non-vanishing. For moderate yaw angles, the wake can be blocked into one of the two allowed deflected positions. The lifetime of the wake, in a given deflected position, is larger by orders of magnitude than the characteristic vortex shedding time. Lifetime distributions follow Poisson-like probability laws, indicating a memoryless process. In this presentation, we propose to review the main results we gathered from several campaigns of measurements on flat backed 3D bluff bodies bluff bodies, over the last five years. We show that this phenomenon is quite generic, as it is observed, with slightly different features, in the wake of axisymmetric bluff bodies and even of spheres. We conclude with perspectives in flow control.

Biography :

Luc R Pastur has expertise in Aerodynamics and Dynamical System Theory. His work on open cavity flows has covered the study of both the shear-layer selfsustained oscillations and centrifugal instabilities that may develop in the inner-flow, at lower Reynolds numbers. More recently, he started to investigate wake bistability of bluff bodies, in collaboration with Olivier Cadot, a phenomenon only recently discovered by the fluid dynamics community, despite its generic occurrence in almost any fluid configurations involving three-dimensional bluff bodies.