Starting: December 2013
The transport of a passive
scalar such as a pollutant, by a high Reynolds number turbulent flow is intimately related to the statistical properties of the fluid particles trajectories. The recent developments of high speed
cameras enabling to track the motion of particles in high velocity flows, gave access to the Lagrangian properties of turbulence (i.e. turbulence seen from the particle’s point of view). In the
last 15 years, studies focusing on homogeneous systems have renewed the experimental approach of turbulence. But most situations of practical interest are inhomogeneous. It is the case of the
atmospheric boundary layer (the few hundred meters above the Earth’s surface), where the flow is extremely turbulent and shows a vertical gradient of velocity.
In this project, a high aspect ratio channel flow will be used as a benchmark case of turbulent boundary layers. This flow exhibits symmetry properties that will make the experimental study simpler. Eulerian measurements will be carried out to fully characterize the flow, and the study will then focus on Lagrangian properties, starting with the acceleration. The dispersion of fluid particles at longer timescales will then be addressed, and the experimental data will be compared to numerical simulations performed by I. Vinkovic and M. Gorokhovski in Ecole Centrale Lyon.
The aim is to better understand the influence of the velocity gradient on the fluid particles trajectories, in order to accurately model the transport properties in this region of the atmosphere.
Polystyrene particles (10 µm) doped with Rhodamine in a turbulent flow. The flow is illuminated by YAG laser sheet and the
fluorescent particles are isolated from the illuminated background by a red filter (exposure time: 1/250 sec).
The first results of this project were presented at the 68th Annual Meeting of the APS Division of Fluid Dynamics in 2015 (read more on the web site of the American Physical Society)
Publication: Stelzenmuller et al. 2017, Lagrangian acceleration statistics in a turbulent channel flow. Physical Review Fluids 2, 054602