Exhaust jet mixing and condensation effects in the near field of aircraft wakes

Abstract

In order to investigate the process of contrail formation, an integral model and a two-dimensional direct numerical simulation have been used to analyse the mixing and entrainment processes of the engine exhaust through their interaction with the vortex wake of various aircraft. The objective of this study is to evaluate the partial vapour pressure of water and temperature in the near field of subsonic and supersonic aircraft. Results are presented involving the saturation calculation by post-processing solution fields which provide a qualitative indicator of the condensation process. After testing the numerical algorithm with some success, this study was performed for three transport subsonic aircraft: A-330, B-737 and DC-9; for the twin-engine ATTAS of DLR and for the Anglo-French supersonic Concorde. For subsonic aircraft, in the early wake, the distance where saturation is reached depends only upon the engine jet characteristics. The engine jet location with respect to the vortex axis has an important influence on the mixing rate and on the saturation evolution. For the supersonic aircraft, a low saturation ratio has been shown along the plume centreline. The wing-tip vortices contribute largely to increase the mixing and dispersion of the exhaust plume. Consequently, the water saturation profiles are clearly changed by the vortical structure. Effects of the aerodynamic parameters are analysed and discussed.