A Numerical Investigation of the Laminar Instability Multi-Tonal Noise of Aerofoils

In the frame of applied aeroacoustics the numerical prediction of the aerofoil self generated noise is key issue for a number of applications in aeronautics, vehicle industry and wind energy. Aerofoil airborne noise has been widely approached in several studies and well characterized for a number of flow conditions. Nevertheless there are still many cases where it is not yet completely clear how the flow noise is generated. The objective of this paper is to perform a deep and accurate analysis of the noise generated by laminar instabilities of the boundary layer arising for Reynolds numbers ranging approximately between 0.6M and 1.1M. The test-case chosen is the NACA 0012 aerofoil which has been investigated by means of transient RANS aerodynamic simulations coupled with the Ffowcs Williams and Hawkings acoustic analogy and a Finite Element based approach to Lighthill´s equation for the acoustic computations. Numerical sound pressure spectra have been compared to experimental data achieving a very good agreement for different flow speeds and Angles of Attack. The numerical simulations performed have been able to capture the sharply peaked multi-tonal acoustic phenomena which arise from the flow instabilities evolving within the boundary layer proving the high potentialities of such numerical approaches in the frame of the applied aeroacoustics.