Visualization of the space-time impulse response of the subcritical wake of a cylinder

The well-known Benard-von Karman cylinder wake is one of the most challengi ng phenomena of fluid mechanics. As the Reynolds number of the flow around a cylinder passes through a critical value, alternating vortex shedding app ears via a Hopf bifurcation. Theoretical studies of the wake have described the appearance of this self-sustained oscillation as the result of a conve ctive to absolute transition resulting in the formation of a global mode. W e illustrate here the convective global regime of the subcritical wake by a nalyzing visualizations of its impulse response.