Lagrangian statistics of light particles in turbulence

TL;DR

This study investigates the Lagrangian velocity and acceleration statistics of micro-bubbles in turbulent water, revealing highly non-Gaussian acceleration PDFs with increased intermittency at higher Reynolds numbers, using advanced particle tracking techniques.

Contribution

It provides new experimental data on micro-bubble acceleration statistics in turbulence, highlighting their intermittency and comparison with other particle types and simulations.

Findings

Acceleration PDFs are highly non-Gaussian with flatness 23-30.

Acceleration intermittency increases with Reynolds number.

Micro-bubbles show slower autocorrelation decay at higher Re.

Abstract

We study the Lagrangian velocity and acceleration statistics of light particles (micro-bubbles in water) in homogeneous isotropic turbulence. Micro-bubbles with a diameter of 340 microns and Stokes number from 0.02 to 0.09 are dispersed in a turbulent water tunnel operated at Taylor-Reynolds numbers (Re) ranging from 160 to 265. We reconstruct the bubble trajectories by employing three-dimensional particle tracking velocimetry (PTV). It is found that the probability density functions (PDFs) of the micro-bubble acceleration show a highly non-Gaussian behavior with flatness values in the range 23-30. The acceleration flatness values show an increasing trend with Re, consistent with previous experiments (Voth et al., JFM, 2002) and numerics (Ishihara et al., JFM, 2007). These acceleration PDFs show a higher intermittency compared to tracers (Ayyalasomayajula et al., Phys. Fluids, 2008) and heavy particles (Ayyalasomayajula et al., Phys. Rev. Lett., 2006) in wind tunnel experiments. In addition, the micro-bubble acceleration autocorrelation function decorrelates slower with increasing Re. We also compare our results with experiments in von Karman flows and point-particle direct numerical simulations with periodic boundary conditions.