Reduction of tonal noise of a NACA 0012 airfoil by roughness elements

Abstract

© 2023, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.An array of cylindrical roughness elements was used to reduce the tonal noise introduced by the separation bubble over a NACA 0012 airfoil at low angles of attack. Experiments were performed for four configurations: a baseline smooth airfoils, two with roughness elements at only one of the airfoil surfaces (pressure side or suction side), and the other with roughness elements at both airfoil surfaces. Arowof spanwise periodically spaced cylinderswas placed close to the mid-chord position in order to induce streaks that render the bubble three-dimensional, decreasing separation and stabilizing the Kelvin-Helmholtz instability of the separated shear layer, which is related to tonal noise. Our results show a decrease, and in some cases the total suppression, of the tonal noise at Reynolds numbers ranging from 0.6×105 to 2.5×105, and angles of attack ranging from 0 to 4 degrees.