On the reduction of aerofoil–turbulence interaction noise associated with wavy leading edges

Abstract

An aerofoil leading-edge profile based on wavy (sinusoidal) protuberances/tubercles is investigated to understand the mechanisms by which they are able to reduce the noise produced through the interaction with turbulent mean flow. Numerical simulations are performed for non-lifting flat-plate aerofoils with straight and wavy leading edges (denoted by SLE and WLE, respectively) subjected to impinging turbulence that is synthetically generated in the upstream zone (freestream Mach number of 0.24). Full threedimensional Euler (inviscid) solutions are computed for this study thereby eliminating self-noise components. A high-order accurate finite-difference method and artefact-free boundary conditions are used in the current simulations. Various statistical analysis methods, including frequency spectra, are implemented to aid the understanding of the noise-reduction mechanisms. It is found with WLEs, unlike the SLE, that the surface pressure fluctuations along the leading edge exhibit a significant source cut-off effect due to geometric obliqueness which leads to reduced levels of radiated sound pressure. It is also found that there exists a phase interference effect particularly prevalent between the peak and the hill centre of the WLE geometry, which contributes to the noise reduction in the mid-to high-frequency range.

Performance and mechanism of sinusoidal leading edge serrations for the reduction of turbulence–aerofoil interaction noise

“…It has been demonstrated by the authors of the current paper Haeri et al 2014;Narayanan et al 2015;Chaitanya et al 2015b;Kim et al 2016) and others that introducing leading edge serrations can be an effective method of reducing far field noise. This previous work was limited in scope and provided no insight in the optimum serration geometry.…”

“…Through numerical simulations based on the compressible three-dimensional Euler equations and a synthetic eddy method for the turbulence generation, Kim et al (2016) investigated the noise reduction mechanisms of sinusoidal leading edge serrated aerofoils. They found that the surface pressure fluctuations along the leading edge exhibit a source cut-off effect due to oblique edge which results in reduced radiated sound power levels.…”

“…Here we show that the optimum serration wavelength, rather than angle, provides a more fundamental interpretation of the experimental noise data. More recent work by Kim et al (2016) has investigated numerically the possible noise reduction mechanism due to leading edge serrations. These noise reduction mechanisms are consistent with the experimental results reported here.…”

Leading Edge Noise Reduction of Thin Aerofoil by the Straight and Curved Serrations of the Add-on Type

“…The second objective of this paper, therefore, is to exploit this unique morphology of the owl wing for the leading edge serration on an aerofoil. As pointed out by Kim et al 6 , the remaining contributor to the interaction noise radiation for a serrated leading edge is related to the flow dynamics at the sawtooth trough region. Because each consecutive sawtooth tips of a curved leading edge serration exhibits a spanwise offset to the sawtooth trough at the downstream, the incoming turbulence structures could be shielded by the sawtooth tip.…”

“…They suggested that the level of broadband noise reduction is a strong function of the serration amplitude h, and is less sensitive to the serration wavelength . An inviscid numerical study by Kim et al 6 exhibited a de-correlation of the surface pressure fluctuation and the far field noise on a serrated leading edge. In particular, the noise source at the mid-region of the oblique edge becomes ineffective across the mid to high frequency range.…”