High-fidelity simulation of contrail formation from jet to vortex phase

Contrails—clouds of ice crystals formed behind aircraft—represent one of the most uncertain contributors to aviation-induced climate forcing. Contrail formation involves complex interactions between jet exhaust dynamics, vortex roll-up and descent, turbulent entrainment, and ice microphysics across multiple spatial and temporal scales. Most large-eddy simulations (LES) of contrails begin at the vortex phase, assuming simplified initial conditions for ice crystal number and size and neglect the highly transient jet phase that precedes it.

We perform high-fidelity simulations using Lagrangian particle-based microphysics models coupled to an LES compressible flow solver. The jet phase is initialized with representative thermodynamic and water vapor profiles, including atmospheric aerosol and soot particles, and lasts a few seconds. The vortex phase, lasting minutes, includes the jet/vortex entrainment, descent and mixing with stratified atmosphere. As the jet phase requires high spatial and temporal resolution, contrail simulations for the vortex phase usually assume an initial jet decayed flow field and ice crystal number and size, thereby neglecting the initial jet phase. In this work, we bridge the two phases by concatenating the jet phase solution over an axial domain length extending up to a maximum of one Crow instability wavelength (~8 times the vortex pair separation), thus providing physically consistent inflow conditions for the vortex-phase simulation.

Our framework allows for the direct propagation of ice crystals from the jet into the vortex phase and is applied to contrails from both kerosene and hydrogen combustion. The results provide more realistic initial conditions for subsequent use in lower-fidelity models that simulate contrail persistence over a timeframe of hours. This work will eventually allow an improved initialization of atmospheric codes and global circulation models.