Droplet growth by turbulent coagulation - Comparison of theory and measurements

While it is well known that cloud droplets grow in an inherently turbulent environment, the role of turbulence is only now being elucidated. Over the course of several decades, both experimental and theoretical studies have come to the conclusion that in-cloud turbulence enhances droplet growth. However, the adequate treatment of turbulence effects on droplet growth still represents a major gap in our understanding of cloud microphysics.

To shed light on this issue, we compare published measurements of droplet growth by collision in turbulent flow with numerical simulations. Since the measurements demonstrate an accelerated growth under turbulent conditions compared to laminar ones, the data clearly cannot be simulated using the well-established kernel for sedimentation under laminar conditions.

However, we show that by employing a collision kernel that has been recently derived from direct numerical simulations we are able to capture the enhancement effect of turbulence for the droplet growth under the experimental conditions adequately and reproduce the experimental data successfully.