Particle Resolved Simulation of Turbulence-Contrail Interactions for the Assessment of Climate Impact

Condensation trails or contrails, which are basically clouds of ice, are the biggest source of aviation impact on the climate. They form when jet exhaust, laden with water vapor and soot particles from combustion, interacts with the cold ambient atmosphere. Numerical modeling of contrails is a current research problem. After contrails form as a collection of ice crystals, they evolve, dilute through entrainment, mix with surrounding air, and eventually disappear. In this study, we focus on the dispersion phase of contrail evolution. The air is turbulent in the lower stratosphere, and to capture turbulence-particle interactions, the smallest scales of flow need to be resolved. We develop a particle-resolved direct numerical simulation model that solves for these eddies and tracks ice particles individually. The role of the exhaust soot, which is a type of condensation nuclei, in determining contrail evolution and persistence is evaluated. We also seek to understand the influence of turbulent fluctuations on contrail properties from a microphysics viewpoint. Particle size distributions are interpreted to recognize the activation of ice crystals and deactivation of soot particles. Different mixing scenarios, falling between two limiting cases- homogeneous and inhomogeneous, are also investigated. Since this work is computationally intensive, we place some emphasis on parallelizing and optimizing our numerical solution algorithms. Results from this research will help determine the climate impact of aviation contrails and formulate mitigation strategies.