Evaluating Bypass Effects of Advanced Turbofan Engines on Contrail Formation Using Large Eddy Simulations

Condensation trails formed behind cruising aircraft engines contribute to climate change through radiative forcing. While most contrail studies consider parameterized single-jet profiles, this CFD study investigates dual-stream jets to characterize turbofan bypass effects on contrail microphysics. High-resolution large-eddy simulations refined early plume dynamics for a dual-stream jet, consisting of a bypass jet and a core jet of air and water vapor (Eulerian phase) laden with soot particles (Lagrangian phase). Microphysical modeling employs a solubility model for soot activation, while the subsequent water vapor condensation processes on activated soot particles and ice growth on freezing particles are computed using a deposition model. The first comparison of a turbofan with its equivalent turbojet showed that the bypass jet enhances the mixing and cooling of the core jet, with a mean particle radius increase of up to 30%. Thereafter, three realistic turbofans—CFM56-5B3/3, LEAP-1A/33, and UHBR— classified, respectively, as medium-bypass-ratio, high-bypass-ratio, and ultrahigh-bypass-ratio engines, were compared at ambient temperatures of 215, 220, and 225 K. The analysis showed that higher bypass ratios enhance jet mixing in the near field, increasing soot activation and droplet freezing processes and resulting in initial contrail properties that are less sensitive to ambient temperatures.