Effects of leading-edge serration shape on noise reduction in rod-airfoil interactions.

Leading-edge serrations inspired by owls exhibit the capability to control airfoil-turbulence interaction noise, but the design principle of the serration shape is still an open issue. To this end, we designed five types of serration shapes with different combinations of curvature, namely, triangular, ogee, anti-ogee, feather-like, and anti-feather-like. These curves are applied to serrated modifications with different bluntness levels (sharp or blunt) and amplitudes (0.05, 0.075, and 0.1 chord length). Considering these serration shapes, 30 cases with various curved types, bluntness levels, and amplitudes are investigated using compressible large-eddy simulation and the acoustic analogy of Ffowcs-Williams and Hawkings on a rod-airfoil configuration. The outcomes reveal a general trend where increased amplitude and blunted serrations are more effective in noise mitigation. Notably, the blunt feather-like (FB) serrations demonstrate the maximum noise reduction capacity across all amplitude levels, decreasing the overall sound power level by up to 2.1 dB. Through multi-process acoustic analysis, source characteristics responsible for generating noise are diagnosed. It is found that noise reduction primarily stems from the change in the source distribution and destructive interference among sound sources, consistent with prior studies. Generally, the serration shape would significantly affect the source distribution and sound interference without altering the fundamental noise reduction mechanisms. The FB shape exhibits the highest concentration of sources at its peaks and roots among all shapes. The presence of concentrated sources in these locations enhances destructive interference, effectively reducing noise emissions. The superior noise-reduction feature of FB serrations should be attributed to both the concentration of sources and the destructive interference. This extensive examination underscores the importance of serration design, especially the potential of FB serrations, in noise control strategies for rod-airfoil configurations, contributing to advancements in aeroacoustic engineering.