Laminar separation bubble effect on the lift curve slope of an airfoil

Abstract

This paper explores some unusual aerodynamic features that can arise due to the existence of laminar separation bubbles which occur at a transitional Reynolds number of 120,000 on two standard NACA airfoils of 21% thickness-to-chord ratio. These effects include an apparent increase in the lift-curve slope beyond the ideal lift slope (2p rad 1) at high angles of attack as well as a sudden stall characteristic. In addition, on one typical airfoil profile, it is demonstrated that negative lift can be generated at low angles of attack. In each case the laminar separation bubble is found to alter the curvature of the external flow, leading to an effective change in the camber of the foil.