Hydrodynamic characteristics in separation bubbles of airfoil under acoustic vortex interaction

Based on the LBM-LES method, aeroacoustic of the NACA0012 airfoil at medium Reynolds numbers was directly simulated. The flow field and aeroacoustic field under acoustic vortex interaction were obtained, and the hydrodynamic characteristics in the shear layer were analyzed. The results show that in the shear layer near the airfoil surface, the T-S wave turns into the K-H instability after the flow separation, and the K-H instability plays an important role in the growth of the disturbance. Turbulence intensity in the separation bubble increases significantly until transition to turbulence, but the turbulence intensity decreases again after the flow reattachment. The large-scale vortex structure of 750 Hz is formed and developed into a stable structure inside the separation bubble, while the vortex structures corresponding to the 2nd and 3rd harmonics are formed after the transition, and developed into stable structures outside the separation bubble. It suggests that the generation mechanism of the 2nd and 3rd harmonic tonal noise is different from that of the 750 Hz fundamental one.