Abstract
Aircraft contrails contribute to climate change through global radiative forcing. As part of the general effort aimed at developing reliable decision-making tools, this paper demonstrates the feasibility of implementing a Lagrangian ice microphysical module in a commercial CFD code to characterize the early development of near-field contrails. While engine jets are highly parameterized in most existing models in a way that neglects the nozzle exit-related aspects, our model accounts for the geometric complexity of modern turbofan exhausts. The modeling strategy is based on three-dimensional URANS simulations of an aircraft nozzle exit involving a bypass and a core jet (Eulerian gas phase). Solid soot and ice particles (dispersed phase) are individually tracked using a Lagrangian approach. The implemented microphysical module accounts for the main process of water-vapor condensation on pre-activated soot particles known as heterogeneous condensation. The predictive capabilities of the proposed model are demonstrated through a comprehensive validation set based on the jet-flow dynamics and turbulence statistics in the case of compressible, turbulent coaxial jets. Simulations of contrail formation from a realistic nozzle-exit geometry of the CFM56-3 engine (short-cowl nozzle delivering a dual stream jet with a bypass rate of 5.3) were also carried out in typical cruise flight conditions ensuring contrail formation. The model provides reliable predictions in terms of the plume dilution and ice-particle properties as compared to available in-flight and numerical data. Such a model can then be used to characterize the impact of nozzle-exit parameters on the optical and microphysical properties of near-field contrails.
Highlights
The continuous growth in air passengers by about 5% per year has increased scientific concerns about the climate impact of commercial aviation.[1]
As part of the general effort aimed at developing reliable decision-making tools, this paper demonstrates the feasibility of implementing a Lagrangian ice microphysical module in a commercial CFD code to characterize the early development of near-field contrails
The computational domain was the twodimensional rectangular box measuring 40Ds × 15Ds based on the half-nozzle model, and the Reynolds-averaged Navier–Stokes (RANS) equations were solved in cylindrical coordinates (O, ⃗⃗r, y)
Summary
The continuous growth in air passengers by about 5% per year has increased scientific concerns about the climate impact of commercial aviation.[1] Cruise flights contribute to global warming through soot and water-vapor emissions from aircraft engines that are responsible for visible white condensation trails (contrails) behind aircraft.[2, 3] Persistent contrails composed mainly of supersaturated ice crystals survive in the atmosphere for several hours and even evolve to form large cirrus formations referred to as aircraft-induced clouds (AIC).[4] The spreading and persistence of this artificial cloudiness in the atmosphere determine their impact on the earth’s radiative balance.[5] Global assessments[6] show that the impact of linear contrails is about 3–9·10-3 W.m-2, while the impact of AIC is 10 times higher,[6] which corresponds to 3 times the impact of aviation CO2 alone.[7] For this reason, the contrail formation process has been a topic of increasing interest in the literature. The following is a short review of main approaches and findings
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