Anisotropy of particle-pair dispersion in bubble-induced turbulence

Bubble-induced turbulence (BIT) plays an important role in mixing, transport and collision of small particles in many natural and industrial applications. In recent years, Lagrangian measurements following the motion of individual fluid tracers have become possible in bubbly flows. A crucial component of the Lagrangian description of BIT is the relative pair dispersion, based on the relative separation of two particles at the respective positions. The present work aims to address the anisotropic property of particle-pair dispersion in BIT. For this purpose, 3D Lagrangian particle tracking measurements are carried out in an octagonal bubble column in which the flow is generated by a homogeneously distributed bubble swarm rising in water. Our results show that the relative dispersion follows the classical ballistic regime at short times. After this, the dispersion transitions to another regime whose behavior depends on the initial separation. We further developed a new method that allows us to quantify and visualize the anisotropy of particle-pair dispersion for varying initial separation vectors. We are currently obtaining improved data to explore and understand in more detail the anisotropic relative dispersion behavior.