Spatiotemporal dynamics at the transition to turbulence

Higgs Centre colloquium

Spatiotemporal dynamics at the transition to turbulence

  • Event time: 1:00pm
  • Event date: 16th September 2015
  • Speaker: Bruno Eckhart (Philipps-Universität Marburg)
  • Location: Higgs Centre Seminar Room,

Event details

Abstract

When Osborne Reynolds documented his observations on the transition to turbulence in pressure driven pipe flow in 1883, he noticed that the turbulence remained localized to regions that extended over the full cross section but did not cover the entire length of the pipe. In recent years similar phenomena have been observed in other flows, and the attention has shifted towards characterizing the  spatio-temporal dynamics of shear flows. The formation of localized  structures from spatially extended ones in subharmonic bifurcations provides organizing elements around which localized turbulent  structures can form. An interesting and unsettled issue concerns the  rate of localization, i.e. exponential vs. algebraic. The possible dynamics of localized turbulent spots includes a decay of the  turbulence, a spreading into the neighboring laminar regions or even the nucleation of new turbulent spots at some distance. This spatio-temporal dynamics has been linked to the phenomenology of directed percolation, and several efforts are under way to measure critical exponents. The spatio-temporal aspects are also relevant for the transition to turbulence in the boundary layer over a flat plate, where dynamical systems approaches  provide an explanation for the nucleation rates and intermittency factors in boundary layer turbulence.