The subject of the paper is the instability of the flow in local regions of laminar boundary-layer separation, the so-called "separation bubbles" that arise in the flow of an incompressible fluid. Typical examples of separated flows of this type are the areas of separation that accompany the flow around airfoils at low Reynolds numbers, geometric surface roughness of various kinds, blunt edges, etc. In accordance with the nature of the flow behind the separation point, a recirculation zone is formed in the laminar or transitional regimes. The aim of this study is the experimental study of the properties of vortical perturbations developing in the flows with the local regions of flow separation including their linear instability with respect to small vortical disturbances, non-linear mechanisms appearing when the velocity fluctuations reach finite amplitude and their nonlocal influence on the basic flow, the mechanisms of formation and strengthening of three-dimensional structure of the basic flow, and effects of three-dimensionality of the surface on the development of disturbances.
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