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, James Clerk Maxwell Building (JCMB) James Clerk Maxwell Building Peter Guthrie Tait Road Edinburgh EH9 3FD GB
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.