The aerodynamic noise from a two-dimensional symmetrical airfoil was studied experimentally using a low-noise acoustic wind tunnel. The measurement of the sound spectrum at Reynolds number 1.6×10 ⁵ indicates the generation of discrete frequency noise from the airofoil at small incidence angles. The surface flow visualizations over the airofoil were carried out using the oil-film method and the shear-sensitive liquid crystal technique. These visualization results indicate that the reattachment and reseparation of the flow occur near the trailing edge of the pressure side of the airfoil, when the discrete frequency noise is generated. The smoke-wire visualization of the flow around the airfoil showed that the strong trailing edge vortices were shed from the airofoil and they form a stable pattern of Karman vortices in the downstream.

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