Bringing clouds into the lab

We investigate experimentally the behavior of droplets in a fully developed turbulent flow, approximating the conditions inside clouds. The rate of collision of the droplets can be enhanced by turbulence. In this experimental study we focus on how droplet sedimentation in a homogeneous and isotropic turbulent flow affects the dynamics of droplets and their mutual interaction: collision, clustering and coalescence of droplets. These effects are monitored by measuring the temporal evolution of droplet size spectrum and also the detection of individual collision events. For this aim we are modulating the turbulence conditions and the dispersity of the droplet collection in the flow. In a truncated icosahedron (soccer ball) chamber with 20 air jets we generate controlled turbulence with specified properties (Reynolds number, dissipation rate, fluctuation velocity). Two different spinning disk droplet generators are used to generate different-size droplets. 3D-Particle Tracking Velocimetry (PTV) with Laser Induced Fluorescence (LIF) tagging is chosen as the experimental method to track the droplets and to detect the mutual interactions. In parallel, droplet size spectrum measurements are carried out using Phase-Doppler Anemometry (PDA). With these tools we will elucidate the interplay of turbulence and droplet interactions