School of Mechanical Engineering Ron Shnap

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SCHOOL OF MECHANICAL ENGINEERING SEMINAR
Monday November 4, 2019 at 14:00
Wolfson Building of Mechanical Engineering, Room 206

Lagrangian Experimental Investigation of
Dispersion in Canopy Turbulence

Ron Shnapp
Ph.D student of Prof. Alex Liberzon

Transport and mixing in the atmospheric surface layer occur, in large part, due to the turbulent flow near the Earth's surface. These two processes govern the dispersal of pollutants, pesticides, pollens, dust or air-borne bacteria in the environment, and are therefore crucial in affecting the economy and our well-being. Turbulence near the surface is commonly generated when a stream of air encounters roughness obstacles on the surface, for example, man-made structures or vegetation - these flows are termed canopy flows. This work presents a novel experimental study, which focuses on the mechanisms at the heart of transport and mixing processes in the canopy flows, as described in the Lagrangian framework.
For this study, we constructed a canopy flow model within the environmental wind-tunnel laboratory, where we conducted measurements through an extended 3D Particle Tracking Velocimetry method. The results of the experiment amount to a unique data set holding millions of tracer particles' trajectories both within and above the canopy layer. Statistical analysis of the 3D trajectories revealed a locally homogeneous and locally isotropic regime of Lagrangian statistics that occurred at small scales. In the seminar, I will present the experiment itself, the locally-homogeneous regime, and statistics of the relative motion between pairs of particles so-called pair dispersion.