On bypass transition in separation bubbles: a review

Zhiyin Yang

Department of Mechanical Engineering and the Built Environment, College of Engineering and Technology, University of Derby, Derby, UK

Abstract: Transition from laminar flow to turbulent flow is of great practical interest as it occurs in many engineering flows and often plays a critical role in aerodynamics and heat transfer performance of those flow devices. There could be many routes through transition, depending on flow configuration, geometry and the way in which transition is initiated by a wide range of possible background disturbances such as free-stream turbulence, pressure gradient, acoustic noise, wall roughness and obstructions, periodic unsteady disturbance and so on. This paper presents a brief overview of wall bounded flow transition in general and focuses more on the transition process in the free shear layer of separation bubbles, demonstrating that at elevated free-stream turbulent intensity the so called bypass transition could occur in geometrically induced separation bubbles where the separation point is fixed.

Keywords: Transition; Bypass transition; Separated free shear layer; Separation bubbles; Free-stream turbulence