The effect of wavy leading edges on aerofoil–gust interaction noise

Abstract

a b s t r a c tHigh-order accurate numerical simulations are performed to investigate the effects of wavy leading edges (WLEs) on aerofoil-gust interaction (AGI) noise. The present study is based on periodic velocity disturbances predominantly in streamwise and vertical directions that are mainly responsible for the surface pressure fluctuation of an aerofoil. In general, the present results show that WLEs lead to reduced AGI noise. It is found that the ratio of the wavy leading-edge peak-to-peak amplitude (LEA) to the longitudinal wavelength of the incident gust (λ g ) is the most important factor for the reduction of AGI noise. It is observed that there exists a tendency that the reduction of AGI noise increases with LEA=λ g and the noise reduction is significant for LEA=λ g ≥0:3. The present results also suggest that any two different cases with the same LEA=λ g lead to a strong similarity in their profiles of noise reduction relative to the straight leading-edge case. The wavelength of wavy leading edges (LEW), however, shows minor influence on the reduction of AGI noise under the present gust profiles used. Nevertheless, the present results show that a meaningful improvement in noise reduction may be achieved when 1:0 ≤LEW=λ g ≤1:5. In addition, it is found that the beneficial effects of WLEs are maintained for various flow incidence angles and aerofoil thicknesses. Also, the WLEs remain effective for gust profiles containing multiple frequency components. It is discovered in this paper that WLEs result in incoherent response time to the incident gust across the span, which results in a decreased level of surface pressure fluctuations, hence a reduced level of AGI noise.

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

“…The relative noise reduction quantified by W (0)/W (h LE ) varying with h LE is plotted in figure 7, where W (0) indicates the SLE case. It is shown in figure 7 that the relative reduction of ATI noise in decibels increases with the amplitude of the WLE profile in an almost linear fashion, which has also recently been observed experimentally by Narayanan et al (2015) and numerically by Lau et al (2013).…”

“…Preliminary investigations on their effectiveness have recently been been reported. Lau et al (2013) performed 3D nonlinear Euler simulations of the noise radiation due to a flat-plate and a symmetric NACA (from 0050 to 0020) aerofoil with various wavy LE (WLE) profiles situated in a mean flow (M ∞ = 0.4 to 0.6) with a harmonic vortical gust. The radiated noise levels were consistently lower than those from the straight LE (SLE) cases.…”

An advanced synthetic eddy method for the computation of aerofoil–turbulence interaction noise

“…high frequencies) compared to the SLE case plotted on the same scale. This result does agree with the early investigation by Lau, Haeri and Kim [15].…”

“…3.3). It has recently been studied by Lau, Haeri and Kim [15] that WLE profiles are effective in reducing ATI noise compared to the SLE case but the existing study relied only on a simple form of vortical gusts (single-frequency velocity excitations). A more comprehensive study based on a realistic 3D turbulence may be achieved by adopting the present SEM approach.…”

“…In this paper, the latest SEM is combined with a sponge-layer technique [13][14][15] that was particularly designed for introducing velocity disturbances as well as absorbing spurious noise. With this combination, the level of spurious noise is kept sufficiently low to guarantee a clean sound field for CAA simulations.…”