Investigation on flow structure and aerodynamic characteristics over an airfoil at low Reynolds number—A review

This Review summarizes the progress in research on the flow structure and aerodynamic characteristics of an airfoil at a low Reynolds number encountered by near-space low-speed aircrafts and micro-air vehicles. The structures of several kinds of laminar separation bubbles and their effect are discussed by drawing on experimental and numerical results reported in the past few decades. The transition process in the separation bubble is detailed from various perspectives, including the receptive, primary instability, secondary instability, and break-down stage. The process of evolution of a coherent vortex structure that may affect the transition is discussed by analyzing the vortex dynamics in the separation bubble. Combined with the flow characteristics at a low Reynolds number and data on the airfoil, aerodynamic characteristics of the airfoil, such as the nonlinear effect and static hysteresis effect at a low angle of attack, are discussed.