Experimental identification of airfoil stall noise sources in static and dynamic conditions

Dynamic stall noise is an important concern in several open rotor applications such as wind turbines. In order to identify the coherent aerodynamic structures responsible for the noise radiation at high angles of attack, a large database of synchronized flow and acoustic measurements have been obtained in an anechoic wind tunnel in both static and dynamic conditions. For a static airfoil at high angle of attack, the velocity fluctuations evaluated from the time-resolved particle image velocimetry data are correlated with acoustic pressure to localize aeroacoustic sources associated with deep stall noise. The noise is strongly linked to the Bénard-von Kármán vortex shedding generated by the interaction of the trailing edge vortex with the Kelvin Helmholtz instability produced in the separation bubble shear layer. For an oscillating airfoil, the reduced frequency is shown to have a significant impact on the flow topology and on the noise radiation. Some distinct features are observed between quasi-static and dynamic stall regimes.