Berlin 2008 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 25: Fluid dynamics I

DY 25.5: Hauptvortrag

Donnerstag, 28. Februar 2008, 12:30–13:00, MA 001

State space properties of linearly stable flows - How does flow in a pipe become turbulent? — •Tobias M. Schneider — Fachbereich Physik, Philipps-Universität Marburg, D-35032 Marburg, Germany

According to most textbooks flow down a straight circular pipe becomes turbulent near a Reynolds number of 2000. However, despite research since 1883 when Reynolds performed his famous experiments, details of the transition mechanism are still not completely understood. This has primarily to do with the absence of a linear instability of the laminar profile for any flow rate, thus making the transition fundamentally different from the ones in the well studied cases of fluids heated from below (Rayleigh-Benard) or between rotating cylinders (Taylor-Couette). The transition in pipe flow is not mediated by any intermediate simple states but rather jumps to a complex flow state immediately. The flow rates at which the onset of transition has been observed vary over a wide range, and there are indications that the turbulent state is not permanent but can decay spontaneously. All these observations are compatible with the formation of a strange chaotic saddle in the system's state space. We will summarize evidence for the existence of this saddle, discuss the properties of the turbulent state and analyze the `edge of chaos' that separates laminar and turbulent dynamics.