Bypass transition in boundary layers as an activated process etc15 Tracking Number 352Presentation: Session: Instability and Transition 5 Room: Room A Session start: 10:30 Thu 27 Aug 2015 Tobias Kreilos tobias.kreilos@epfl.ch Affifliation: Emergent Complexity in Physical Systems Laboratory (ECPS), \'Ecole Polytechnique F\'ed\'erale de Lausanne, CH-1015 Lausanne, Switzerland Taras Khapko taras@mech.kth.se Affifliation: Linn\'e FLOW Centre, KTH Mechanics, Royal Institute of Technology, SE-100 44 Stockholm, Sweden Philipp Schlatter pschlatt@mech.kth.se Affifliation: Linn\'e FLOW Centre, KTH Mechanics, Royal Institute of Technology, SE-100 44 Stockholm, Sweden Yohann Duguet duguet@limsi.fr Affifliation: LIMSI-CNRS, Universit\'e Paris-Sud, UPR 3251, F-91403, Orsay, France Dan S Henningson henning@mech.kth.se Affifliation: Linn\'e FLOW Centre, KTH Mechanics, Royal Institute of Technology, SE-100 44 Stockholm, Sweden Bruno Eckhardt bruno.eckhardt@physik.uni-marburg.de Affifliation: Fachbereich Physik, Philipps-Universit\"at Marburg, 35032 Marburg, Germany Topics: - Instability and transition, - Wall bounded flows Abstract: We consider the spatio-temporal aspects of the transition to turbulence in a boundary layer above a flat plate exposed to free-stream turbulence. Combining results from the receptivity to free-stream turbulence with the observation of a double threshold from transition studies in e.g. pipe flow we arrive at a physically motivated prediction for the spatial distribution of nucleation events in boundary layers. We use a cellular automaton to implement a complete model for the spatial and temporal evolution of turbulent patches and show that the model reproduces the statistical features of the boundary layer remarkably well. The success of the modeling shows that bypass transition occurs as a spatiotemporally activated process, where transition is triggered by critical fluctuations imported from the free-stream turbulence. |