Large-eddy simulations of flow (M=0.2, Re_c=1×10~6) past a full-span flap at two angles-of-attack are performed in an effort to understand the flow unsteadiness and noise generation mechanisms. Two types of acoustic waves are categorized. They are: (Ⅰ) high-frequency acoustic waves radiated from the suction surface of the main wing, and (Ⅱ) high-frequency acoustic waves radiated from the trailing edge of the main wing and the flap. Increasing the angle-of-attack does not change the noise components. The radiation of the high-frequency acoustic waves from the suction surfaces is related to a transition/reattachment mechanism. The trailing-edge noise is generated because of the successive vortex forming and shedding in the main-wing and flap wake. Its generation has less dependence on the status (turbulent or laminar) of the incoming boundary layer developing on the two sides of the trailing edge.
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