  We investigate the ability of 4D Particle Tracking Velocimetry measurements
at high particle density to explore intermittency and irreversibility in a
turbulent swirling flow at various Reynolds numbers. For this, we devise
suitable tools to remove the experimental noise, and compute the statistics of
both Lagrangian velocity increments and wavelet coefficients of the Lagrangian
power (the time derivative of the kinetic energy along a trajectory). We show
that the signature of noise is strongest on short trajectories, and results in
deviations from the regularity condition at small time scales. Considering only
long trajectories to get rid of such effect, we obtain scaling regimes that are
compatible with a reduced intermittency, meaning that long trajectories are
also associated with areas of larger regularity. The scaling laws, both in time
and Reynolds number, can be described by the multifractal model, with a
log-normal spectrum and an intermittency parameter that is three times smaller
than in the Eulerian case, where all the areas of the flow are taken into
account.
