Unsteady Aeroacoustic Sources from a Dynamically Stalled Plunging Wing under Micro Aerial Vehicle Conditions

This experimental study showcases the aeroacoustic sources measured on a NACA0012 airfoil subjected to dynamic stall due to sinusoidal plunging motions. The flow fields are measured on the upper surface of the airfoil using time-resolved particle image velocimetry (PIV), and the broadband surface pressure fluctuations were measured using a flush-mounted microphone probe and the reconstructed pressure field from PIV. Boundary layer separation occurs as the plunging airfoil approaches the maximum plunging velocity. A dynamic stall vortex (DSV) forms on the upper surface near the leading edge. Pressure distribution over the upper surface evolves in response to the movement of the DSV, with the lowest surface pressure observed at the DSV location. Full boundary layer separation results in a temporary reversal of the adverse pressure gradient, and the lowest pressure during moments of full detachment is at the trailing edge. The overall magnitude of the power spectral density (PSD) of the surface pressure fluctuations increases during the stages near the maximum plunging speed, with greater increases observed for the downstroke phase where the DSV is proceeding over the surface. The low-frequency tonal peaks observed at both the DSV location during downstroke and the maximum velocity during upstroke. However, high-frequency broadband fluctuations were measured from the DSV passage during downstroke. These variations of the surface pressure and its broadband components indicate significant unsteady loading and broadband noise sources from a plunging wing.