Abstract
Abstract. The dispersion of aircraft emissions during the vortex phase is studied using a 3-D LES model with Lagrangian particle tracking. The simulations start with a fully rolled-up vortex pair of a type B747/A340 airplane and the tracer centred around the vortex cores. The tracer dilution and plume extent is studied for a variety of ambient and aircraft parameters until aircraft-induced effects have ceased. For typical upper tropospheric conditions, the impact of stratification is more dominant compared to turbulence intensity or vertical wind shear. Moreover, the sensitivity to the initial tracer distribution was found to be weak. Along the transverse direction, the tracer concentrations can be well approximated by a Gaussian distribution, along the vertical a superposition of three Gaussian distributions is adequate. For the studied parameter range, the vertical plume expansion ranges from 400 m to 550 m and cross-sectional area from 4.0 × 104 m2 to 6 × 104 m2 after six minutes. For validation, selected simulations were compared to an alternative LES model and to in-situ NO-measurements.
Highlights
From the wake-vortex dynamics point of view, it is convenient to distinguish three phases in the life cycle of an aircraft wake (Hoshizaki et al, 1975): During the jet regime the vorticity sheet around the wings rolls up into two counterrotating vortices
We found that the secondary vorticity structures, which evolve along the vortex-pair oval, and the primary vortex reconnection and ring formation control the heterogenization of the tracer along flight direction on small and large scales, respectively
A large eddy simulation (LES) model with Lagrangian particle tracking has been employed to study the dilution of aircraft emissions during the first minutes behind an aircraft
Summary
From the wake-vortex dynamics point of view, it is convenient to distinguish three phases in the life cycle of an aircraft wake (Hoshizaki et al, 1975): During the jet regime the vorticity sheet around the wings rolls up into two counterrotating vortices. When the vortex pair descends most of the exhaust is stored in that primary wake and, sinks below flight level. The evolution of aircraft plumes during the vortex phase is important to study for several reasons. Unterstrasser et al.: Dimension of aircraft plumes: effect of wake vortices presented results have implications, both for nonlinear plume chemistry and for the microphysical evolution in a contrail. The focus of the present study is on the impact of wake vortices on the tracer distribution rather than on the wake vortex evolution itself. This is followed by thorough sensitivity analyses varying stratification, ambient turbulence, linear vertical wind shear, vortex initial circulation, and initial spatial distribution.
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