Date de présentation: Mai 2023
Auteur(s): Parisa Afkari, Mohamed Chouak, François Garnier
Conférence: CSME-CFD 2023, Sherbrooke, QC, Canada
https://savoirs.usherbrooke.ca/handle/11143/20979
Abstract
The study of aircraft contrails involves several physical and chemical processes at various spatial and temporal scales, from contrail formation near the engine exhaust up to contrail cirrus at a large scale depending on the atmospheric conditions. Given the impact of near field jet characteristics on the contrail life cycle, characterizing the dynamic and microphysical properties of jet contrails has been emphasized. Within the large eddy simulation (LES) framework, the modeling of contrail formation in literature is mostly performed using a temporal approach by assuming axial gradients negligible as compared to radial ones, which is only valid far from the engine nozzle. In contrast, the spatial LES approach is more rigorous and allows for modeling the entire jet development with no assumptions. Moreover, based on the changing concentrations of water vapor in the upper troposphere, and the difficulties in measuring that, modeling the aircraft engine in different levels of relative humidity in the atmosphere is crucial. As such, we propose to use a spatial LES to better characterize the dynamic and microphysical properties in the near field of an aircraft exhaust at cruise level for two cases in different ambient conditions in terms of relative humidity value. A high-order (six orders in space and three orders in time) compressible computational fluid dynamic (CFD) code, FludiLES, was used along with an ice-only microphysical model to investigate contrail particles in an Eulerian-Lagrangian approach. Model validation of 1st and 2nd order statistics of turbulence with experimental results showed a good agreement in the case of a round jet. Furthermore, contrail microphysical properties (saturation ratio, particle radius, and optical depth) were characterized in the case of the CFM56-3 engine. The analysis of results at two ambient relative humidity 60% and 130% confirmed literature findings; the case of saturated ambient conditions leads to larger ice particles and with plume age, fewer particles are evaporated as compared to the lower relative humidity case.
