Effect of gravitational acceleration on particle entrainment in turbulent-turbulent interfaces

Droplet-laden turbulent flows have been studied widely in homogeneous turbulence, generating insights into particle dynamics in those conditions. Interfaces between areas of different turbulent intensities are present in many phenomena relevant to environmental or industrial applications. A better understanding of turbulent-turbulent interfaces would lead to a better understanding of complex physical processes that are still open problems, such as warm-rain formation. Cumulonimbus clouds present sharp interfaces between highly turbulent droplet-laden air and low turbulence unladen ambient air. Different factors influence the dynamics of the particles at the interface. In this experimental study, we investigate the effect of the orientation of the interface with respect to gravity on particle entrainment in a T/T interface. Experiments inside a low-speed wind tunnel capture the dynamics of droplets with turbulent scaling representative of those found in clouds. We investigate preferential concentration and settling velocity of the droplets by performing particle tracking and Phase Doppler Particle Analysis. Keeping particle and turbulent interface characteristics identical, we compare cases with different alignment of the interface respective to gravity, shedding new light on the effect of orientation of the interface, e.g., the cloud boundary, on the particle dynamics due to the interaction with turbulence.