Abo Bibliothek: Guest
Ninth International Symposium on Turbulence and Shear Flow Phenomena
June 30 - July 3, 2015, University of Melbourne, Australia

DOI: 10.1615/TSFP9

LAGRANGIAN EVOLUTION OF HAIRPIN STRUCTURES IN THE TEMPORAL TRANSITION IN CHANNEL FLOW

pages 667-672
DOI: 10.1615/TSFP9.1120
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ABSTRAKT

A Lagrangian study on the evolution of vortical structures in the Klebanoff-type temporal transitional channel flow is reported. Based on the Eulerian velocity field from the direct numerical simulation, a backward-particletracking method is applied to solve the transport equation of the Lagrangian scalar field. and then the iso-surfaces of the Lagrangian field can be extracted as Lagrangian material surfaces in the evolution. It is noted that the Lagrangian surface, which is initially a vortex surface, is demonstrated as a good approximation of a vortex surface before significant topological changes. Thus the Lagrangian structures can be used to represent the evolution of vortical structures in the early transition. The evolution of a typical Lagrangian surface is presented. The near-wall Lagrangian surface can evolve from a streamwise-spanwise sheet to a triangular bulge, and then into the signature hairpin-like structure. By comparing the Lagrangian results with the vortical structures identified by Eulerian vortex identification criteria, differences between Lagrangian and Eulerian structures are discussed. In particular, the Lagrangian approach can elucidate the continuous temporal evolution of vortical structures in transitional wall flows.

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