Leading edge serrations for the reduction of aerofoil self-noise at low angle of attack, pre-stall and post-stall conditions

Jung-Hoon Kim,Seyed Mohammad Hasheminejad,Paruchuri Chaitanya,Muhammad Farrukh Shahab,Phillip Joseph,Giovanni Lacagnina,Kwing-So Choi,Tim Berk,Alfredo Pinelli,Bharathram Ganapathisubramani,Mohammad Omidyeganeh,Oksana Stalnov,Tze Pei Chong

doi:10.1177/1475472x20978379

Abstract

This paper addresses the usefulness of leading edge serrations for reducing aerofoil self-noise over a wide range of angles of attack. Different serration geometries are studied over a range of Reynolds number [Formula: see text]. Design guidelines are proposed that permit noise reductions over most angles of attack. It is shown that serration geometries reduces the noise but adversely effect the aerodynamic performance suggesting that a trade-off should be sought between these two considerations. The self-noise performance of leading edge serrations has been shown to fall into three angle of attack (AoA) regimes: low angles where the flow is mostly attached, moderate angles where the flow is partially to fully separated, and high angles of attack where the flow is fully separated. Leading edge serrations have been demonstrated to be effective in reducing noise at low and high angles of attack but ineffective at moderate angles. The noise reduction mechanisms are explored in each of three angle regimes.

Highlights

Leading edge serrations are shown to provide noise reductions in selfnoise at relatively low angles of attack,[7] In this paper we explore their potential for reducing aerofoil self-noise over a wide range of angles of attack, including pre-stall and post-stall conditions
Leading edge serrations have greatest influence on the boundary layer at low frequencies, This behaviour is broadly consistent with the difference in noise reduction spectra plotted in Figure 9(a), with the exception being in the frequency range 1 < fc=U < 4, which we have shown in equation (3) is related to the size of the separation bubble, which cannot be detected in the wake turbulence
This paper has investigated the performance of leading edge serrations for reducing aerofoil self- noise over a wide range of angles of attack, including pre-stall and post-stall conditions

Summary

Introduction

Leading edge serrations are well known to be able to enhance the aerodynamic performance of aerofoils[1,2,3] and in reducing their noise due to the interaction with turbulent in-flow.[4,5,6,7] Leading edge serrations are shown to provide noise reductions in selfnoise at relatively low angles of attack,[7] In this paper we explore their potential for reducing aerofoil self-noise over a wide range of angles of attack, including pre-stall and post-stall conditions. Control of aerofoil self-noise at these range of attack angles and the reason behind it does not appear to have been addressed in previous literature. The far-field self-noise generated by an aerofoil at low to moderate angle of attack is caused by the interaction between pressure fluctuations over the surface convecting past the trailing edge. At low AoA, where the flow remains attached over the entire surface, these hydrodynamic pressure fluctuations arise from the turbulent boundary layer in direct contact with the surface. At higher angles of attack, where the flow becomes separated from the trailing edge, the pressure fluctuations on the surface are the result of the near field from the turbulent shear layer

Objectives

Methods

Results

Conclusion