Airfoil noise reductions through leading edge serrations

TLDR

This study investigates whether leading‑edge serrations can reduce broadband noise from aerofoil–turbulence interaction. Experiments were conducted on a flat plate in an open‑jet wind tunnel using grid‑generated isotropic turbulence, with sinusoidal leading‑edge serrations of varying wavelength λ and amplitude 2h, and results were compared to straight‑edge plates and a serrated NACA‑65 aerofoil. The results show that leading‑edge serrations yield negligible noise reduction at low frequencies but significant mid‑frequency reductions (up to ~9 dB for flat plates and ~7 dB for the aerofoil), with the amplitude 2h being the key parameter for enhancing sound‑power reduction.

Abstract

This paper provides an experimental investigation into the use of leading edge (LE) serrations as a means of reducing the broadband noise generated due to the interaction between the aerofoil’s LE and impinging turbulence. Experiments are performed on a flat plate in an open jet wind tunnel. Grids are used to generate isotropic homogeneous turbulence. The leading edge serrations are in the form of sinusoidal profiles of wavelengths, λ, and amplitudes, 2h. The frequency and amplitude characteristics are studied in detail in order to understand the effect of LE serrations on noise reduction characteristics and are compared with straight edge baseline flat plates. Noise reductions are found to be insignificant at low frequencies but significant in the mid frequency range (500 Hz–8 kHz) for all the cases studied. The flat plate results are also compared to the noise reductions obtained on a serrated NACA-65 aerofoil with the same serration profile. Noise reductions are found to be significantly higher for the flat plates with a maximum noise reduction of around 9 dB compared with about 7 dB for the aerofoil. In general, it is observed that the sound power reduction level (ΔPWL) is sensitive to the amplitude, 2h of the LE serrations but less sensitive to the serration wavelength, λ. Thus, this paper sufficiently demonstrates that the LE amplitude acts as a key parameter for enhancing the noise reduction levels in flat plates and aerofoils.