Trailing edge noise reduction using velvety serrations

This work studies the trailing edge noise reduction potentials of combining trailing edge serrations and porous membrane/velvet structures made of non-woven fabrics. Anechoic wind tunnel experiments were conducted based on a flat plate model, at a chord-based Reynolds number between 2 × 10⁵ and 5 × 10⁵ and zero angle of attack, with fully tripped boundary layers. Different alignment conditions between the serrations and the undisturbed wake flow were tested. It was observed that the noise reduction capability of the conventional serrations deteriorates significantly when the serrations were misaligned with the flow, while the performances of the combined structures were only slightly affected by misalignment. The porous membrane structure was found to generate extra high-frequency noise, while the porous velvet structure effectively suppressed the high-frequency noise. In addition, porous velvet structures with serrated trailing edge provided additional noise reduction at lower frequencies, which is likely due to the additional destructive interference at the serrated end of the porous velvet structure. The optimal combination could achieve approximately 10 dB noise reduction in a wide frequency range, in both flow-aligned and flow-misaligned conditions. Further hotwire wake survey revealed the possible mechanisms for the additional noise reduction capability of the combined treatments.