Catastrophic events in separated flow theory.

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The study of flow separation from the surface of a solid body, and thedetermination of global changes in the flow field that develop as a result of the separation, are among the most fundamental and difficult problems of fluid dynamics. Separation not only alters the form of trajectories of fluid particles around the body, but also leads to a significant change in the values of the aerodynamic forces acting on the body.The behaviour of separated flow is quite complicated. For example, when a thin aerofoil is placed in subsonic flow, and the angle of attack is gradually increased, the separation is first observed at the leading edge of the aerofoil. It manifests itself through the formation of a small bubble of reversed flow near the leading edge. Catastrophic separation arises when for increased angles of attack, or changes in geometry, the bubble suddenly bursts and is replaced by a massive separation region covering almost the whole aerofoil. This causes drastic changes to aerodynamic properties such as lift and drag.The proposed research is aimed at furthering our understanding of separated flows. The emphasis will be on ``blow-up'' phenomena and post-catastrophic behaviour of separated flows. We intend to show that there is a relationship between these phenomena and nonlinear instability of separated flows.