Simulation and characterization of the laminar separation bubble over a NACA-0012 airfoil as a function of angle of attack

Abstract

This study examines the effects of angle of attack on the characteristics of the laminar separation bubble (LSB), its associated low-frequency flow oscillation (LFO), and the flow field about a NACA-0012 airfoil at Reynolds number of 5×104 and 9×104, Mach number of 0.4, and several angles of attack near stall. In the range of the investigated angles of attack, statistics of the flow field suggest the existence of three distinct angle-of-attack regimes. At angles of attack lower than the stall angle of attack, the mean flow field is attached, a short bubble is formed, and the flow field is not much affected by the LFO. At angles of attack higher than the stall angle of attack and lower than the angle of attack of maximum LFO, the flow field undergoes a transition process in which the LFO develops until the flow field reaches a quasiperiodic switching between separated and attached flow and the LSB switches between short and long bubble. At angles of attack higher than the angle of attack of maximum LFO, the mean flow field is massively separated, an open bubble is formed, and the LFO gradually loses momentum and becomes unable to reattach the flow until the airfoil approaches the angle of a full stall. These angle-of-attack regimes have, to the best of the authors' knowledge, not been reported in the literature before.