Sur la nature de la première bifurcation des écoulements interdisques

The transition to unsteadiness is studied by direct numerical simulation. A direct transition from steady to chaotic behavior is observed for a Reynolds number 1 % above threshold. The convective instability of the stator boundary layer seems to be related to the direct transition to chaos. Low spatial resolution can trigger the radial convective instability of the boundary layer. It is shown that the curvature induces sharp gradients which require high spatial resolution. Nevertheless, the Hopf bifurcation responsible for the transition to periodic solutions has been located independently of mesh refinement.