Ivan De Visscher

Aircraft wake vortices in stably stratified and weakly turbulent atmospheres: simulation and modeling

This study investigates the influence, on aircraft wake vortex behavior, of atmospheres that are stably stratified (neutral to very strong) and weakly turbulent, by means of large-eddy simulations at very high Reynolds number and on relatively fine grids. The atmospheric fields are first generated using large-eddy simulations of forced and stratified turbulence reaching a statistically stationary state. The obtained fields are shown to be realistic and consistent with the literature. A pair of counter-rotating vortices, with relatively tight cores, is then put in the obtained fields and evolved. The evolution of the wake vortex topology, transport, and decay is analyzed in depth by measuring the wake vortex characteristics in all cross planes. The vortex transport and deformation are related to the stratification and turbulence levels. Stratification combined with weak turbulence is seen to strongly affect the Crow instability development. Different decay mechanisms are identified, related to the interactions with the turbulence, the turbulent baroclinic vorticity, and/or between the vortices themselves. Finally, improved simplified models of vortex altitude evolution and of vortex decay (with two phases) are proposed and calibrated on the present results. They yield good agreement with the large-eddy simulation results and are usefully integrated in our operational models. Read More: http://arc.aiaa.org/doi/abs/10.2514/1.J051742

Vortex Particle-Mesh simulations of atmospheric turbulence effects on wind turbine blade loading and wake dynamics

We develop a Vortex Particle-Mesh (VPM) method for the Large Eddy Simulation of wind turbine wakes and coarse scale aerodynamics.

Design Principles for a Separation Support Tool Allowing Optimized Runway Delivery

The research in the wake vortex domain made possible in the last years to tackle airport capacity issues by designing new concepts for wake separations between aircraft on approach and departure. Those new solutions allow for dynamic wake separation reduction depending on aircraft characteristics and weather conditions. Amongst those concepts are found Time-Based Separation (TBS), RECAT Pairwise (RECAT-PWS) and Weather Dependent Separation (WDS). However, the application of dynamic separations entails the use of a spacing delivery support tool. This tool shall compute the applicable timeor distance-based separation minima and provide distance indicators supporting their correct delivery by the controller. Distance indicators have hence to account for aircraft separation compression effects but also for the uncertainties related to aircraft speed and wind evolution. This paper presents the principles used for the design of a demonstrator of such a separation delivery support platform called LORD. The LORD tool makes use of a methodology to mitigate separation infringement and to prevent aircraft under spacing by using an additional buffer on the spacing computation. The use of such buffers allows the separations to be correctly delivered up to a certain ‘failure rate’ equivalent to what is currently observed at airports while still providing capacity benefits with a better spacing management by the controller in different separation modes (e.g. distance based or time based). To prevent spacing infringement, different support warnings are also implemented in the tool. These warnings are to be used as safety nets to quickly identify potential issues in the approach/landing phase and allow the controller to take corrective actions. The LORD tool was successfully tested by Air Traffic Controllers during Real-Time Simulation campaigns. The use of the new separation concepts together with the LORD tool is seen to allow for an increase of throughput and reduction of separation infringement, while maintaining workload and situation awareness at an acceptable level.

Analysis of extreme aircraft wake vortex circulations

Because of its take-off, an aircraft generates a wake essentially made of a pair of counter-rotating vortices notably characterized by their total circulation. In this test case, we analyze the evolution of wake vortex total circulation with the extreme value theory. It consists in estimating the probability that a wake vortex circulation exceeds a given threshold for a fixed set of CMC samples