Three-Dimensional Massively Separated Flows over Wings

Three-dimensional massively separated flows around finite wings at high angles of attack exhibit complex dynamics. The wakes feature large-scale flow structures, including the separation bubbles, stall cells, shear layers, tip vortices, leading- and trailing-edge vortices, arch vortices, and ram's horn vortices. Smaller vortices also emerge from the breakdown of the larger structures through various instability mechanisms. The collection of the large-scale flow features strongly influences the three-dimensional nature of the flow and the forces exerted on the wing. The planform parameters of aspect ratio, sweep, taper ratio, and twist determine the structures and instabilities that are accentuated in the wake, giving rise to a wide variety of behaviors. These wake dynamics have been studied extensively over the last decade in coordinated experimental, computational, and theoretical investigations across a range of Reynolds numbers. In particular, modal and nonmodal linear global stability analyses of the three-dimensional separated flows have provided enhanced physical insights and supported the design of flow control strategies. The effectiveness of control approaches for massively separated flows has been verified by companion experiments for both laminar and turbulent regimes. This review summarizes research efforts that have elucidated large-scale separated flow characteristics and universal flow features across different wake regimes in translating wings from low to moderate Reynolds numbers. The findings from these efforts provide a foundation for a deeper understanding of massively separated flows at higher Reynolds numbers and suggest potential opportunities for wake analysis of wings experiencing dynamic motion and gusts.