Regensburg 2007 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 24: Poster I

DY 24.56: Poster

Mittwoch, 28. März 2007, 16:00–18:00, Poster D

Statistical analysis of coherent structures in transitional pipe flow — Tobias Schneider, Bruno Eckhardt, and •Jürgen Vollmer — Fachbereich Physik, Philipps Universität, 35032 Marburg, Germany

The transition to turbulence in pipe flow is an outstanding problem in fluid dynamics. Although linear stability theory suggests that the laminar state always remains stable, the transition to turbulence occurs at rather moderate flow speeds. Recently, computer simulations and the numerical discovery of unstable travelling waves have supported a transition scenario that is inspired by ideas from dynamical systems theory. According to these ideas, the transition is connected with a strange saddle that forms in the state space of the system in the neighbourhood of the travelling waves. One indicator for this saddle is the transient appearance of the travelling waves in the flow field. Time traces of correlation functions clearly show regions dominated by four or six vortices, in agreement with experimental observations. We study the time spent near each travelling wave and characterise the dynamics by transition probabilities between the states. This allows us to make a first and empirically feasible step towards an analysis of the turbulence characteristics in terms of travelling waves.