## Experimental study of turbulent multiphase flows : inertial particles, collisions and bubble dynamics

Turbulent multiphase flows encompass some of the biggest open questions in modern fluid mechanics. The dynamics of solid particles, liquid droplets and gas bubbles represent significant gaps in our fundamental understanding, while at the same time, being of great relevance in many industrial and environmental applications. There are multiple examples of the relevance of these problems, but I will focus on the formation of rain in warm clouds as a classical example where the poor basic understanding hinders progress in accurate modeling and prediction of the underlying geophysical, or engineering, process.

I will discuss laboratory experiments in which we probe the inertial effects in the dynamics of heavy particles in a homogeneous isotropic turbulent flow. The interaction of the inertial particles with the turbulent vortical structures results in accumulation of droplets in regions of high strain and the modification of the drift velocity of droplets due to gravity. Both of these effects lead to a higher probability of collisions due to smaller inter-droplet distance and higher relative velocities.

I will also describe results for the same problem at the opposite side of the density ratio spectrum : The dynamics of bubbles in turbulent flows. I will conclude with a brief description of a new study to understand the behaviour of microbubbles under the effect of shear and ultrasound-induced forces.