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Colloquium by Haitao Xu (Tsinghua University)

The Lagrangina View of Fluid Turbulence

Abstract:

Fluid flow becomes turbulent when the destabilizing inertial effects overwhelm the damping effects due to viscosity or friction. High Reynolds number turbulence is characterized by a flux of energy from the scale at which the energy is supplied into the flow to the scale at which the energy is dissipated. Understanding this energy flux is at the center of turbulence research. Traditionally, studies of turbulence have been almost exclusively in the Eulerian frame, i.e., in a coordinate system fixed in or at a prescribed motion relative to the laboratory frame. The last 15 years witnessed significant development in the Lagrangian viewpoint, i.e., following “fluid particles (tracer particles)” that move with the fluid in high-Reynolds-number turbulent flow field, in both experiments and numerical simulations. The new perspective revealed many interesting properties of turbulence and advanced our understanding, but also posed intriguing questions. Here we report recent Lagrangian Particle Tracking measurements conducted in a high-Reynolds number von Kármán swirling water flow between two counter-rotating and show how the measurements connect the motion of fluid particles with some fundamental properties of turbulence, such as the energy flux through scales and the time irreversibility.
Time: January 4th, 2017, 14:30 pm
Venue: A601, NAOC

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