This paper presents a series of novel trailing-edge treatments, including designs of curved-serrated, porous, porous-serrated and serrated-porous geometries on a flat-plate extension attached to a NACA0012 airfoil. The trailing edge noise performance of the proposed designs has been investigated at low-to-moderate Reynolds numbers (1.9×10~5 to 3.2×10~5) and compared with a baseline flat-plate extension. The overall sound pressure level (OASPL) from 250 Hz to 10000 Hz is found to be reduced of up to 16.4 dB by curved-serrations. This resulted from the attenuation of boundary layer instability and bluntness vortex-shedding noise. Porous structures are found to produce significant high-frequency-broadband noise, whose level increases with the increase of flat-plate open area and Reynolds number. The combination of serrated and porous geometries (serrated-porous designs) are found to suppress the instability tonal noise and consistently achieve noise reduction on OASPL of up to 14.2 dB at low-to-moderate Reynolds number (1.9×10~5 to 3.2×10~5). Flow characteristics in the very near wake of the proposed trailing edges have also been investigated at a Reynolds number of 2.9×10~5. Fluctuating velocity data show a strong correlation with far-field acoustic data, indicating that the proposed designs influence trailing-edge noise generation by altering the flow characteristics around the trailing edge rather than the noise scattering efficiency.
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