Lagrangian acceleration measurements via PTVA (Particle Tracking Velocimetry and Accelerometry) on a turbulent-like flow

Quasi-two-dimensional turbulence (Q2D) has both a practical and theoretical relevance. Following the topological approach, turbulent-like flows have the aim to model and study some of the aspects of turbulence. With this target, in the laboratory of the Imperial College London, Q2D electromagnetically-controlled multiple-scale flows are experimentally studied. To study those flows, an accurate Lagrangian technique to measure acceleration is needed: a novel technique, Particle Tracking Velocimetry and Accelerometry (PTVA), based on Image Analysis techniques, has been designed, developed and validated. PTVA is a self-adaptive methods which relies on a number of positions to approximate the trajectories that adapts to the topology and acceleration of the flow and grants much more precise measurements compared to previous methods. PTVA has allowed to experimentally measure all the Navier-Stokes equation’s terms over the entire investigation field, to classify zero acceleration points, to extract the map of power input and output along with the one of the divergence of acceleration (stirring intensity), measured for the first time, obtaining the tools to work on mixing efficiency. The pdf of the acceleration components has turned out to be very similar to the one usually measured in real turbulence: as this pdf has been often considered as the signature of turbulence, this result makes the question of which characteristics of turbulence generate which features arise.