Björn Hof

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How turbulence arises in simple shear flows, such as pipes and channels has
been an open question for over a century. In these flows turbulence is found
despite the linear stability of the laminar flow and transition is caused by
finite amplitude perturbations. Despite numerous experimental and
theoretical studies it has not been possible to determine a well defined
critical point nor to clarify the nature of the transition. It will be shown
for the examples of pipe and Couette flow that the onset of sustained
turbulence is a nonequilibrium phase transition. The critical point is
determined by resolving the extremely long time scales of the underlying
growth and decay processes. By detailed numerical simulations and
experimental measurements close to the transition point we also determine
the critical exponents and show that this transition falls into the directed
percolation universality class.

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IST Austria
Hörsaal III der Physikalischen Institute
Contact: Joachim Krug