Particle trapping in three dimensional fully developed turbulence

The statistical properties of fluid particles transported by a three dimensional fully developed turbulent flow are investigated by means of high resolution direct numerical simulations. Single trajectory statistics are investigated in a time range spanning more than three decades, from less than a tenth of the Kolmogorov timescale, $\tau_{\eta}$, up to one large-eddy turnover time. Our analysis reveal the existence of relatively rare trapping events in vortex filaments which give rise to enhanced intermittency on Lagrangian observables up to $10 \tau_{\eta}$. Lagrangian velocity structure function attain scaling properties in agreement with the multifractal prediction only for time lags larger than those affected by trapping.