Aircraft Wake Sensing and Tracking Strategies towards Operational Formation Flight: Assessment of data assimilation, reinforcement learning and control approaches within large eddy simulations by Ignace RANSQUIN

For the degree of Doctor of Engineering Sciences and Technology

Every year, migratory birds liven the sky up by aligning in arrows and drawing impressive V-shapes. The energetic efficiency of this flying technique is explained by the existence of a wake in a region behind every individual and that each can perceive. Just like birds, airplanes also leave a wake consisting of two parallel vortices made visible in the sky by the condensation trails of the engines. Just like birds, are airplanes also able to take advantage of the wake of an aircraft in front of them? This thesis is devoted to bringing some elements of answer to that question by focusing on the concept of extended formation flight characterized by a several tens of wingspan distance between the leader and the follower, and by studying its impact on the air traffic.

The swirling movement of the air around the leader’s wake encountered by the following aircraft explains the benefits of the formation flight technique but can also lead to hazardous dynamic effects such as strong rolling moments. Nevertheless, those effects are disseminated information that can be interpreted by the follower in order to detect the position of the leader’s wake. In large eddy simulations, we aim to reproduce all those effects, from the aerodynamics of the aircraft to their six-degrees-of-freedom dynamics.

Then, we exploit control and data assimilation tools designed to predict the characteristics of the leader’s wake without requiring direct visual information. We show that the tracking of the wake can be performed using controllers built either from model-based Ensemble Kalman Filters or from model-free Reinforcement Learning techniques. We highlight observability issues related to the prediction of the wake characteristics and we use an appropriate mathematical framework to quantify that observability in order to optimize the wake tracking controllers. Finally, thanks to the development of methodology that combines both space-developing and time-developing simulations, we study the impact of formation flight on the long-term dynamics of the wake resulting from the two-aircraft formation. We highlight the strong asymmetry of the wake and the impact of the uncertainty of the relative position between the leader and the follower on its dynamics. We show the difference of this wake with the one produced by an isolated aircraft.

Jury members :

• Prof. Philippe Chatelain (UCLouvain, Belgium), supervisor
• Prof. Aude Simar (UCLouvain, Belgium), chairperson
• Prof. Grégoire Winckelmans (UCLouvain, Belgium)
• Prof. Julien Hendrickx (UCLouvain, Belgium)
• Prof. Mattia Gazzola (University of Illinois Urbana Champain, USA)
• Mr. Jordan Adams (Airbus, France)

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