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DY: Fachverband Dynamik und Statistische Physik
DY 3: Fluid Physics of Turbulence
DY 3.10: Vortrag
Montag, 16. März 2020, 12:15–12:30, ZEU 118
Asymmetries of Lagrangian Coherent Structures — •Gerrit Maik Horstmann1,2, Jeffrey Tithof2, and Douglas H. Kelley2 — 1Institute of Fluid Dynamics, Helmholtz-Zentrum Dresden - Rossendorf, Bautzner Landstr. 400, 01328 Dresden, Germany — 2Department of Mechanical Engineering, University of Rochester, Rochester, New York 14627, USA
Lagrangian coherent structures (LCSs) are the dominant barriers to mixing in a fluid flow. LCSs are either the most repelling or most attracting material surfaces in the flow over a given time interval and are computed using velocity fields evolving either forward or backward in time, respectively. Using data from different 2D and 3D laboratory experiment and direct numerical simulations (DNS), an asymmetry between repelling and attracting LCSs growing with the Reynolds number is revealed. In 2D, this asymmetry is characterized by attracting LCSs occurring over a larger fraction of the spatial domain and moving in a more irregular way than repelling LCSs. Studying an analytical model that captures the salient features of this asymmetry, it can be argued that LCS asymmetry is tied to the direction of the energy cascade in turbulence and exhibits opposite trends in 2D versus 3D. In the 3D flows, it is further observed that attracting LCSs are stronger than repelling LCSs indicating the existence of a second, possibly independent, asymmetry. These results are partially connected to recent discoveries of temporal asymmetry in turbulence suggesting LCSs as an alternative analyzing tool for studying some fundamental properties of turbulent flows.