  Lagrangian statistics of passive tracers in rotating turbulence is
investigated by Particle Tracking Velocimetry. A confined and steadily-forced
turbulent flow is subjected to five different rotation rates. The PDFs of the
velocity components clearly reveal the anisotropy induced by background
rotation. Although the statistical properties of the horizontal turbulent flow
field are approximately isotropic, in agreement with previously reported
results by van Bokhoven and coworkers [Phys. Fluids 21, 096601 (2009)], the
velocity component parallel to the (vertical) rotation axis gets strongly
reduced (compared to the horizontal ones) while the rotation is increased. The
auto-correlation coefficients of all three components are progressively
enhanced for increasing rotation rates, although the vertical one shows a
tendency to decrease for slow rotation rates. The decorrelation is
approximately exponential. Lagrangian data compare favourably with previously
reported Eulerian data for horizontal velocity components, but show different
behaviour for the vertical velocity components at higher rotation rates.

Fluid Dynamics