Newsletter 35

The transition to turbulence in pipe and plane Couette flow differs from the better understood situation of Taylor-Couette or Rayleigh-Bénard flow in that the laminar profile is stable against infinitesimal perturbations for all Reynolds numbers. Moreover, even when turbulent flow is established, it can spontaneously return to laminar flow. These observations are compatible with the formation of a strange chaotic saddle known from dynamical system theory. Here we focus on the dynamics near the boundary between laminar and turbulent dynamics. Applying the iterated edge tracking algorithm we compute the relevant hyperbolic structures intermediate between laminar and turbulent dynamics and relate our findings to the classical saddle-node bifurcation scenario.