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COMPARATIVE STUDY OF LAGRANGIAN EVOLUTION OF DISTURBANCES: VORTICITY VERSUS MATERIAL LINES

Barak Galanti
High Performance Computing Unit of the IUCC, Tel-Aviv University, Tel-Aviv 69978, Israel

Dmitri Gendler- Fishman
Department of Fluid Mechanics and Heat Transfer, School of Mechanical Engineering, Tel-Aviv University, P.O. Box 39040, Tel-Aviv 69978, Israel

Alexander Liberzon
School of Mechanical Engineering, Faculty of Engineering, Tel Aviv University, Ramat Aviv 69978, Israel

Arkady Tsinober
Department of Fluid Mechanics and Heat Transfer, School of Mechanical Engineering, Tel-Aviv University, Tel-Aviv, Israel; and Institute for Mathematical Sciences and Department of Aeronautics, Imperial College, London, United Kingdom

Abstrakt

The evolution of disturbances in turbulent flows is studied here using direct numerical simulations (DNS) and experimentally using three dimensional particle tracking velocimetry (3D-PTV) through a Lagrangian tracking of pairs of particles. The disturbances are presented as an evolving differences between the vorticity vectors of the initially closed particles and also infinitesimal material lines, attached to the particles. There is a striking dissimilarity of the evolution of active turbulent quantities, such as vorticity as compared to the passive objects such as material lines. The gained insight in the differences is important for progress in understanding of the mechanisms involved in genuine turbulence and evolution of passive objects.