Experimental Investigation of Near-Field Aeroacoustic Characteristics of a Pre- and Post-Stall NACA 65-410 Airfoil

The present study reports an experimental investigation of the near-field aeroacoustic characteristics of a cambered NACA 65-410 airfoil. The experiments were performed in an aeroacoustic wind tunnel facility at a moderate chord-based Reynolds number of 4.2×105. Detailed static and dynamic surface pressure information was recorded to reveal the pre- and post-stall dynamics. By varying the angle of attack from 7° to 15°, a stall behavior similar to thin airfoil stall is observed from the evolution of the static and dynamic surface pressure spectra at different chordwise locations. Moreover, while the surface pressure spectra show a monotonic decrease with constant gradients after entering full stall, the pre-stall behavior shows a different trend and partly resembles the attached and stalled flows. Furthermore, the unsteady surface pressure spectra are compared to those obtained from a NACA 0012 airfoil, showing notable differences in the near-field stall dynamics. A scaling formula proposed by a previous study is applied to the present pressure spectra and found to scale well except for measurements close to the leading edge. The present near-field measurements and the streamwise and spanwise length scales can be useful input to the modeling of airfoil separation and stall noise for cambered airfoils.