Aerodynamics and Aeroacoustics of Dynamic Stall of a Pitching NACA 65-410 Airfoil

The unsteady aerodynamic and near-field pressure response of a cambered NACA 65-410 airfoil undergoing oscillatory pitching motion is investigated experimentally. Measurements are performed in a low-turbulence wind tunnel and combine surface pressure measurements, phase-averaged particle image velocimetry (PIV), and time–frequency analysis. Two pitching cases are examined: a low-frequency case (kr = 0.02, a0 = 7◦, Aˆ = 8◦) and a higher-frequency case (kr = 0.10, a0 = 12◦, Aˆ = 8◦). The low-frequency case is characterized by trailing-edge separation, light stall, and delayed reattachment, resulting in pronounced hysteresis in the aerodynamic loads. The corresponding near-field pressure response exhibits chord-dependent surface pressure fluctuations distributed over frequency and phase, without sharp, localized energetic events in either the cycle-averaged power spectral density or the time–frequency representations. In contrast, the higher-frequency case is dominated by dynamic stall vortex (DSV) formation, downstream convection, and interaction with the trailing-edge, leading to large transient load amplification and strongly phase-dependent pressure fluctuations. Phase-averaged spectrograms and signal energy content reveal a clear chordwise delay in the pressure response and identify three distinct energy peaks at x/c = 0.3 associated with DSV formation, convection, and reattachment. The results further clarify the physical origin of a previously unexplained secondary energy peak, attributing it to the downstream convection of the leading-edge vortex following its formation and partial lift-off from the airfoil surface.