Aircraft wake sensing and tracking strategies towards operational formation flight : assessment of data assimilation, reinforcement learning and control approaches within large eddy simulations

Every year, the sky comes to life with migratory birds that line up and draw 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. Are airplanes also able to take advantage of the wake of an aircraft in front of them? This thesis is dedicated to bringing some answers to that question by focusing on the concept of extended formation flight, and by studying its impact on the air traffic management. The swirling movement of the air around the leader’s wake encountered by the following aircraft explains the benefits of the formation flight technique. However, this movement can lead to hazardous dynamic effects such as strong rolling moments. If properly controlled, those effects are also disseminated information that can be exploited 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 a 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.