Rotating turbulence

Aim of this project is the experimental investigation of the influence of background rotation on turbulent flows. The project focuses on the anisotropic effects of the Coriolis force on turbulent particle-pair dispersion, quantifying this anisotropy through the comparison of the horizontal (normal to the rotation axis) dispersion and the reduced vertical one. Experiments of electromagnetically forced turbulence are performed in a tank (0.5 m), put on a rotating table: the magnetic field of an array of permanent magnets below the tank interacts with the ions of the NaCl solution, which are set in motion by the electric field generated in the lowest 30 mm with two linear titanium electrodes. This forcing induces a highly 3D turbulent flow in the lowest region of the container, which decays along the upward direction. The background rotation is varied between 0 and 5.0 rad/s (Rossby number between infinity and 0.11 in the forced region).

With Particle Tracking we have access to the three Lagrangian velocity components in a 3D domain, hence to gradients and correlations in all directions, and to dispersion data. The newly-designed PTV system consists of four high speed cameras and a LED array as a continuous light source, and is able to track more than a thousand particles in a volume comparable with the integral scale of the flow, and with space- and time-resolution adequate to fully resolve the Kolmogorov scales.

3D-PTV measurements are performed in a 120 mm side cubic volume at mid-height, and in a 70 mm side low-height one. The figures refer to these latter measurements and show the recovered trajectories and an example of Lagrangian velocities and accelerations from a 10 s image sequence of continuously forced flow.