This study experimentally investigates the impact of streamwise finlet height on the three-dimensional turbulent structures and wall-pressure fluctuations over a NACA0018 airfoil. The presence of finlets of three heights all induces two pairs of counter-rotating streamwise vortices, leading to a pronounced lifting effect behind them, followed by a recovery process downstream. The intensity of this lifting effect strongly depends on the finlet height. Short finlets convey the original streak structures upward, maintaining a spatial distance from the wall. Differently, the medium-height and tall finlets disrupt the streamwise velocity streaks in the turbulent boundary layer and generate new hairpin-like vortices in the detached shear layer. The stronger lifting effect displaces turbulent structures away from the wall, leading to a significant reduction in Reynolds shear stress and pressure fluctuations in the mid- and high-frequency bands. The best pressure reduction performance is obtained for median-height finlets. Excessively tall finlets introduce additional turbulent structures, thereby elevating low-frequency wall-pressure fluctuations and compromising high-frequency suppression.
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