Wake Vortices and Boundary Layer Interaction

The interaction between wake vortices from an upstream body and a downstream boundary layer is significant for both fundamental and practical aspects of fluid mechanics. An in-depth understanding of the underlying flow physics is crucial for numerous problems in aeronautics, architectonics, and energy related to the complex interferences between different bodies or apparatuses. The incoming wake vortices can generally be divided into streamwise, vertical, and spanwise vortices based on their axial directions relative to the coordinate system of downstream boundary layer. They interact with the downstream boundary layer in different ways. However, the spanwise wake vortex has more profound effects on the downstream boundary layer than the other two, because it simultaneously disturbs the whole span region of boundary layer. Therefore, the vortex dynamics of interaction between spanwise wake vortices and a downstream boundary layer is focused on in this review. The efforts of unveiling the flow physics related to this kind of interaction with different canonical configurations are reviewed as the geometrical complexity increases. The wake-triggered spanwise secondary vortices and the laminar-to-turbulent transition routine caused by their destabilization are highlighted in particular. The transition process characterized by the evolution of secondary vortices is distinct from that of a natural transition or a bypass transition induced by freestream turbulence and is commonly encountered in flows around complex geometries. Finally, areas that deserve more attention in future work are outlined and discussed.