Optimization of the poro-serrated trailing edges for airfoil broadband noise reduction.

Tze Pei Chong,Elisa Dubois

doi:10.1121/1.4961362

Abstract

This paper reports an aeroacoustic investigation of a NACA0012 airfoil with a number of poro-serrated trailing edge devices that contain porous materials of various air flow resistances at the gaps between adjacent members of the serrated-sawtooth trailing edge. The main objective of this work is to determine whether multiple-mechanisms on the broadband noise reduction can co-exist on a poro-serrated trailing edge. When the sawtooth gaps are filled with porous material of low-flow resistivity, the vortex shedding tone at low-frequency could not be completely suppressed at high-velocity, but a reasonably good broadband noise reduction can be achieved at high-frequency. When the sawtooth gaps are filled with porous material of very high-flow resistivity, no vortex shedding tone is present, but the serration effect on the broadband noise reduction becomes less effective. An optimal choice of the flow resistivity for a poro-serrated configuration has been identified, where it can surpass the conventional serrated trailing edge of the same geometry by achieving a further 1.5 dB reduction in the broadband noise while completely suppressing the vortex shedding tone. A weakened turbulent boundary layer noise scattering at the poro-serrated trailing edge is reflected by the lower-turbulence intensity at the near wake centreline across the whole spanwise wavelength of the sawtooth.

Highlights

Engine jet noise used to be the major noise source for a civil aircraft
Turbulators were applied at 0.15 C from the leading edge, and on both sides of the airfoil, in order to ensure that turbulent boundary layers are generated before reaching the trailing edge
A prominent feature for this type of serrated trailing edge is the exposure of a significant bluntness (e) at the root region, which would otherwise be negligible for the conventional flat plate type serrated trailing edge

Summary

Introduction

Engine jet noise used to be the major noise source for a civil aircraft. Its dominance in aviation noise has been less significant since the introduction of a high bypass ratio aero-engine. Noise generated at the trailing edge of engine fan blades, or the airframe’s high lift devices, has become more important. The noise mechanism here is related to the scattering of turbulent energy in the boundary layer into noise at the trailing edge. At high Reynolds numbers, the boundary layer that develops over the airfoil surface is turbulent and the radiated noise from the trailing edge is largely broadband in nature. The concern on the aircraft noise represents an important constraint on maintaining the growth in capacity of the airport transport system

Objectives

Methods

Conclusion