A CFD–LES Framework for Simulating Contrail Formation from Ammonia Aviation Fuels

by Torge Bohlken, Ph.D. Student, University of South Florida, tbohlken@usf.edu

Contrail formation is one of the most significant non-CO2 climate impacts of aircraft operations, outweighing the radiative forcing from CO2 emissions by almost a factor of two. Understanding differences in microphysical evolution and optical characteristics between contrails produced by traditional and carbon-free aviation fuels is, therefore, crucial to ensuring the successful development of climate-friendly propulsion systems. While ammonia is considered a promising hydrogen-based fuel alternative, its contrail formation and persistence characteristics remain uncertain owing to unique thermodynamic conditions in the aircraft’s wake. While soot, acting as a primary nucleation site in contrails produced by traditional fuels, is absent in the ammonia-system’s exhaust, water vapor emissions are significantly increased, and contrail nucleation may still occur on ambient aerosol populations at upper tropospheric levels. To assess the climate impacts of ammonia-powered contrails, a specialized CFD contrail module has been developed within the atmospheric code Meso-NH, based on the microphysical parameterization LIMA (Liquid Ice Multiple Aerosols) and coupled with anelastic and pseudo-incompressible formulations. To reconcile the significantly varying spatial and temporal scales throughout a contrail’s lifetime, the model couples two temporal LES domains specialized to the jet, vortex, and early-dissipation regimes by superimposing synthetic atmospheric and wake-turbulence fields. The development of this model paves the way to enabling the first detailed simulation-backed comparison of optical and persistence characteristics between contrails produced by ammonia and kerosene.