Biography
Biography: Luc R Pastur
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 memory-less 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.
Figure 1: mean flow field (color map and streamlines) in the wake and pressure distribution (open dots) at the rear and top of a commercial car.
Recent Publications
1. M Grandemange, O Cadot, M Gohlke (2012) Reflectional symmetry breaking of the separated flow over three-dimensional bluff bodies. Physical Review E. 86(3):035302.
2. M Grandemange, M Gohlke O. Cadot (2013) Turbulent wake past a three-dimensional blunt body. Part 1. Global modes and bi- stability. Journal of Fluid Mechanics. 722:51:84.
3. M Grandemange, M. Gohlke, O. Cadot (2014) Turbulent wake past a three-dimensional blunt body. Part 2. Experimental sensitivity analysis. 752:439-461.
4. A Evrard, O Cadot, L R Pastur (2015) Imperfect supercritical bifurcation in a three-dimensional turbulent wake. Physical Review E. 91(6):063005.