Tonal Noise prediction of SD7037 Airfoil using 3D Large Eddy Simulation Approach

In this article, noise generation mechanisms are studied at different Reynolds numbers and angles of attack. Tonal noise is the major part of airfoil noise at low Reynolds numbers. Studying the tonal noise and the effects of Reynolds number and angle of attack is challenging in aeroacoustics. 3D numerical simulation is conducted using the large eddy simulation method on SD7037 airfoil. Sound propagation is computed using the Ffowcs Williams-Hawkings (FW-H) analogy. The numerical results are validated using available experimental results. Some discrete peaks and a dominant peak exist in frequency spectra at low angles of attack. Increase of Reynolds number and the angle of attack decreases the number of discrete peaks and at high angles of attack and the dominant peak is diminished too. Studying the flow features shows that when a laminar boundary layer covers a vast area of the suction side, it can amplify acoustic waves that are generated in wake of the airfoil and this mechanism causes a dominant peak in the acoustic spectrum. Amplifying Tollmien-Schlichting waves by shear layer in laminar separation at suction side cause the discrete peaks and when a transition occurs in the airfoil suction side, discrete peaks are diminished. In the original semi-empirical Brooks, Pope and Marcolini (BPM) formulation, the boundary layer thickness of the pressure side is usually used as the length scale and it is replaced by the suction side boundary layer thickness. The results predict the frequency and amplitude of tonal noise successfully.