Effects of jet/vortex interaction on contrail formation in supersaturated conditions

Abstract

The effects of the interaction between a model of aircraft trailing vortex and engine jets on the formation of a contrail in supersaturated ambient air are studied using Eulerian-Lagrangian two-phase flows large-eddy simulations. The three-dimensional structure of the contrail, the mean flow properties, and the statistical correlations between ice and water vapor are analyzed for different jet and vortex parameters and different soot particle numbers. The interaction is characterized by the entrainment of the jets by the trailing vortex. In the four-engines case, particles exhausting the outboard jets are exposed to local higher supersaturation due to the temperature drop in the low-pressure vortex core region. The soot particle number affects both the structure and the global characteristics of the contrail. The increase in soot loading results in stronger vapor depletion – which leads to larger ice production – and to smaller ice particles for a given amount of vapor exhaust. The fraction of activated particles decreases with soot loading because of the increased competition for the vapor available for condensation. Of particular interest is the interaction between the jet/vortex turbulence and ice microphysics (activation, condensation, particle size distribution, and optical depth). It is found that the characteristic timescales of mixing and condensation can be of the same order in the jet regime. For the present high ambient supersaturation conditions, the competition between the entrainment of humid ambient air and vapor depletion plays an important role in determining the initial growth of the contrail and the spatial and size distributions of ice particles.