Review of Unsteady Vortex Flows over Slender Delta Wings

摘要

A wide range of unsteady phenomena relevant to slender vortex flows over stationary and maneuvering delta wings is reviewed. The origin, characteristics, and physical mechanisms of these unsteady phenomena and their role in buffeting are discussed. Dynamic response of leading-edge vortices for maneuvering wings and mechanisms of hysteresis and time lag effects are reviewed. Issues and challenges for unsteady vortex flows over delta wings are outlined. Although the main features of the unsteady phenomena related to slender delta wings are relatively well understood, many aspects require further study. The details of the shear layer instabilities, steady and unsteady substructures, and transition need to be investigated further, Vortex wandering remains a problem in the characterization of the leading-edge vortices. Time-averaged velocity in the core of a wandering vortex is not representative of instantaneous core structure. The relationship between the shear layer instabilities and vortex wandering requires further study. The main instability associated with vortex breakdown is the helical mode instability, and the spiral form of breakdown is a consequence of this instability of the breakdown wake. The mechanisms of vortex interactions, which appear in the form of antisymmetric oscillations of breakdown locations, need to be investigated further. Whether vortex breakdown is a necessary part of these interactions is not known. Although these kinds of vortex interactions are thought to be dominant over slender wings, they also, surprisingly, exist over nonslender wings. These interactions may take very complicated forms when excited by ek-ternal disturbances. The frequency spectrum of the unsteady flow phenomena that exist over stationary wings is very wide, which is one of the challenges in numerical simulations of these flows. Vortex breakdown, vortex interactions, and vortex shedding, either alone or in combination, play an important role in wing. and fin buffeting, although vortex breakdown is the main source of buffeting over slender wings.