Unsteady Modes in the Flowfield about an Airfoil with a Horn-Ice Shape

Abstract

An experimental investigation was conducted on an NACA 0012 airfoil with a leadingedge horn-ice shape to identify and characterize flowfield unsteadiness related to ice-induced flow separation. This type of iced-airfoil flowfield is dominated by a leading-edge separation bubble, which is associated with several inherent modes of unsteadiness. Using unsteady surface pressure and wake velocity measurements, three distinct modes of unsteadiness were identified at various locations throughout the flowfield. These unsteady modes included a regular mode of vortical motion and a shear-layer flapping mode, which are both associated with separation bubbles. A low-frequency mode was also observed that was associated with the thin-airfoil stall type of the iced airfoil, and was represented by a global oscillation of the airfoil circulation. The characteristic frequencies, convective qualities, and flowfield locations corresponding to these unsteady modes were compared with those reported in the literature for iced-airfoil flowfields and flows about canonical geometries.