Progress in analysis and prediction of dynamic stall,” J. Low Reynolds number airfoil survey, volume 1,” Technical Report No. , Google Scholar CrossrefĪirfoil self-noise and prediction,” Technical Report No. Google ScholarĪirfoil trailing-edge flow measurements,” AIAA J. Mechanics of Flow-Induced Sound and Vibration (Īcademic Press, New York). Google ScholarĪerodynamic sound generation of flapping wing,” J. , Google Scholar Crossref, ISIĪ review of trailing edge noise generated by airfoils at low to moderate Reynolds number,” Acoust. Noise generated by airfoil profiles placed in a uniform laminar flow,” J. Larger pitching frequency or amplitude results in lower peak level of the noise humps. In one pitching period, the moment when the narrow-band noise hump occurs is independent from the pitching amplitude and it is delayed as the pitching frequency increases. The occurrence of the noise humps was attributed to the laminar boundary layer separation. At the corresponding moment, a coherent vortex street convecting on the airfoil surface was observed, and the vortex shedding frequency was in good agreement with the central frequency of the noise hump. The short-time Fourier transformation results of the noise signals revealed that a high-level narrow-band noise hump occurred at a specific angle of attack in a pitching cycle. A microphone was placed in the far-field and the particle image velocimetry technique was utilized to study the flow structures near the trailing edge. Cases with the pitching amplitude varying from 7.5° to 15° and frequency from 3 to 8 Hz were tested, corresponding to the reduced frequency from 0.094 to 0.25. The pitching motion was in sinusoidal functions with a mean incident angle of 0°. In this study, the far-field noise from a pitching NACA 0012 airfoil was measured at a Reynolds number of 6.6 × 10 4.
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