Experimental study of the aeroacoustic behavior of a pitching NACA65-410 airfoil

Abstract

This study experimentally investigates a NACA65-410 cambered airfoil undergoing oscillating pitching motions at a chord-based Reynolds number of ${\mathrm{Re}}_c=4.2\times 10^5$. Two reduced frequencies, $k_r=0.023$ and $k_r=0.052$, were tested. Results show that increasing the pitching amplitude and frequency leads to higher far-field noise. Surface pressure fluctuations are generally comparable or higher in the pitching cases compared to static case, except in deep stall where the static cases showed stronger fluctuations. Phase-averaged surface pressure spectrograms reveal significant differences between dynamic and static cases, with four distinct flow regimes emerging around stall onset and flow reattachment. These regimes are sensitive to $k_r$, mean angle of attack, and pitching amplitude, while maintaining consistent characteristics. Asymmetric behavior in surface pressure fluctuations and overall sound pressure level is observed, particularly at higher $k_r$. Coherence maps along the chordwise direction reveal an increase in coherence at higher angles of attack, which further intensifies as flow separates from the airfoil, where the convecting structures to the downstream dominate the flow. These findings are crucial for advancing the design and noise mitigation strategies of airfoils in applications such as rotorcraft, wind turbines, and unmanned aerial vehicles, where dynamic stall and associated acoustic emissions impact performance and environmental compliance.