  We investigate the growth in the spanwise direction of turbulent spots
invading a laminar flow in a plane Couette flow. Direct Numerical Simulation is
used to track the nucleation of streaks during the spot growth. Experiment and
direct numerical simulation allow us to study the velocity of the spot fronts
and of the vortices observed at the spots' edges. All these results show that
two mechanisms are involved when turbulent spots grow: a formerly proposed
local growth occurring at the spot spanwise tips but also in comparable
proportion a global growth induced by large-scale advection identified in the
present work.

Fluid Dynamics