Non-Equilibrium Phase Changes in Aircraft Exhaust: A Computational Study on Early Contrail Formation

Abstract: A numerical framework is developed to model contrail formation in the near-field exhaust of aircraft engines, resolving non-equilibrium phase transitions in compressible, multi-component, non-ideal fluid flows. The approach combines well-established methods from steam turbine modeling for liquid-phase transitions with cloud microphysics models for ice formation. It resolves homogeneous and heterogeneous nucleation, interphase momentum exchange, and polydispersed size distributions of droplets, ice crystals, and soot particles. These models are implemented in a parallelized finite-volume solver and applied to a high-bypass turbofan exhaust configuration with simplified geometry. Results indicate that non-equilibrium effects strongly influence condensation and freezing dynamics, while nozzle geometry and water vapor content modulate local supersaturation and phase transition pathways. The findings underscore the limitations of equilibrium-based models and highlight the value of physics-based, scalable tools for analyzing contrail formation across fuels and propulsion systems.