Geometry Effect of Streamwise Finlet on Manipulating Wall-Pressure Fluctuations

This study examines how streamwise finlet geometry manipulates turbulent boundary-layer structures to attenuate wall-pressure fluctuations and reduce trailing-edge noise with a limited drag penalty. Three finlet configurations mounted on a NACA0018 airfoil are compared by separately modifying the leading-edge and rear profiles. Flow-field measurements show that all finlets disrupt the original near-wall streaky structures and redistribute vortical structures within the boundary layer, which reduces wall-pressure fluctuations and yields similar far-field noise reduction. However, the different drag penalties among the three configurations indicate that finlet shape can be optimized to reduce drag while preserving the acoustic benefit. The leading-edge profile changes the interaction between the incoming flow and the finlets, thereby modifying the onset and wall-normal position of the detached shear layer. A more gradual leading edge reduces the velocity deficit and drag penalty, but places the shear layer closer to the wall, which slightly weakens the wall-pressure fluctuation and noise reduction. The rear profile mainly affects local low-speed and reverse-flow events near the finlet rear. A smoother rear profile suppresses these nearwall events and reduces high-frequency velocity fluctuations, leading to a lower drag increase.