Mode and regime identification for a static NACA0012 airfoil at transitional Reynolds numbers

Abstract

This work examines the flow structure modes in the boundary layer and in the wake of a NACA0012 airfoil in static conditions at transitional chord-based Reynolds numbers (Rec), for small angles of attack (α). A laminar mode, with a laminar separation of the boundary layer and laminar Kármán streets in the wake, was first observed for Rec< 61400 andα= 0°. For 77 000 < Rec< 118600, which corresponds to a regime between laminar and transitional mode called subcritical mode, the boundary layer exhibited a long separation bubble reattached close to the trailing edge, and the wake showed a turbulent Kármán street. Finally, for higher Recandα, a critical transition mode consisted of a long bubble followed by a turbulent separation, and a less structured vortex street in the wake of the airfoil.