Directed percolation transition to turbulence

Björn Hof
IST Austria
Directed percolation has recently emerged as the likely solution to the century old riddle surrounding the onset of turbulence in simple shear flows. In pipes and ducts turbulence typically arises even though the laminar base flow is linearly stable. The resulting large scale flow patterns are characterized by the co-existence and the competition between laminar and turbulent domains. Although analogies between the dynamics of laminar turbulent fronts and directed percolation have already been proposed more than 30 years ago subsequent studies observed a discontinuous, non-universal scenario instead. I will here present a series of recent experiments that for the first time provide access to the excessive spatial and temporal scales that are relevant at the onset of turbulence and can hence clarify the nature of the transition.