CONICET | Buscador de Institutos y Recursos Humanos

The phenomenon of turbulence is relevant due to its presence in a wide variety of flows, from atmospheric and oceanic flows, to industrial ones. It has the property of being highly efficient in the transport and mixing of substances and particulate matter which are advected by the flow, such as volcanic ashes in the air or plastic waste on the surface of the sea. In order to better comprehend the physics behind these processes, it is necessary to study the dynamics of the flow from a Lagrangian viewpoint. The present work focuses mainly in studying the behaviour of the Lagrangian velocity structure functions (LVSF).We present the results of an experimental study carried out in an inertially driven turbulent von Kármán swirling flow generated by two counter-rotating impellers fitted with straight blades, and reaching an integral Reynolds number of order 1x10^5. The working fluid, water, is seeded with neutrally buoyant 6 mm spherical particles, whose size comparable to the integral scale of the flow. The trajectory of each individual particle is measured by PTV, for a duration of several integral times, within the whole experimental volume (20 x 20 x 20 cm^3). From their trajectories we derive the lagrangian velocities and accelerations for each particle. In order to compare our experimental results with numerical data, we perform direct numerical simulations of the Navier-Stokes equation using a Taylor-Green forcing in a cubic box with 768^3 mesh points, for Re ~ 1x10^4. In the simulations, the flow is seeded with 1x10^6 Lagrangian particles whose evolution is followed for several integral times.Our results indicate that the mean structure of the flow, present both in the DNS and the experiment, plays an important role in the scaling laws observed in the LVSF. See: https://statphys27.df.uba.ar/registration/index.php/SP27/MainConference/paper/view/553