HRT

Abstract

We study the transition from laminar flow to fully developed turbulence in a von Karman flow (Re from 50 to 106). The flow undergoes a classical succession of bifurcations driven by the destabilization of the azimuthal shear-layer. We observe that the transition to turbulence is globally supercritical: the kinetic energy of the velocity fluctuations can be used as a single order parameter to characterize the transition. We also measure the dissipation through the torque injected in the flow. For high Reynolds numbers, the mean flow presents multiple solutions: the canonical symmetric solution becomes marginally unstable towards a flow which breaks the basic Rπ-symmetry. The global bifurcation between these states is highly subcritical and the system thus keeps a memory of its history. The transition recalls low-dimension dynamical system transitions and exhibits slow dynamics and peculiar statistics. References F. Ravelet et al., J. Fluid Mech. 601, 339 (2008) F. Ravelet et al., Phys. Rev. Lett. 93, 164501 (2004)