Analysis of Aerodynamic Sound Sources in a Flow Around a Two-Dimensional Airfoil Under Stalled Conditions

Abstract

In this paper, we discuss an identification of aerodynamic sound sources in a flow around a two-dimensional NACA0012 airfoil at a Reynolds number of 2×105 to 5×105 under stalled conditions. This study is carried out mainly by experimental method based on the results by the measurement of surface pressure, unsteady flow, resulting far-field sound with high accuracy. Also, the computation was performed by Large-Eddy Simulation (LES) for an incompressible flow. Then, we investigated under the light stall condition (LS) when long bubble formed and under the deep stall condition (DS) when completely stalled. As a result, peaks were observed at a Strouhal number of 0.5 to 0.6 not only in aerodynamic sound spectra but also in surface pressure spectra, the coherence spectra between surface pressure and aerodynamic sound, and the coherence spectra between flow velocity and aerodynamic sound. The flow measurements indicate that the vortices based on Strouhal number of 0.5 to 0.6 formed outside of the separated shear layer. Also, some results showed that strong sound sources existed near the airfoil surface in LS but the sound sources disappeared in DS. This is due to the difference in whether the separated flow passes near the suction surface or not.