On the aerodynamic and aeroacoustic characteristics of a NACA 65-410 airfoil at moderate Reynolds number

The present study investigates the flow dynamics and self-noise generated by a highly instrumented NACA 65-410 airfoil, which aims to provide a better understanding of the near-field aerodynamic and aeroacoustic characteristics and their correlation with airfoil noise. The experiments have been carried out in an aeroacoustic wind tunnel at two moderate Reynolds numbers, Re = 422,000 and 633,000, respectively, based on airfoil chord length. By varying the airfoil angle of attack through -2 to 15 degrees, the flow transits from attached to fully separated (i.e. stall). The results have shown that the magnitude of the power spectral density (PSD) of the surface pressure fluctuations grows with increasing angle of attack, and furthermore a clear distinction exists between attached and separated flow characteristics. Furthermore, the near-field coherence between the chord-wise microphones revealed the development of large-scale structures convecting across the chord length of the airfoil as the flow begins to separate. The autocorrelation analyses of the surface pressure measurements also suggest that such large scale structures in the separated flow may vary in sizes as the Reynolds number increases.