Noise Reduction Mechanisms of an Airfoil with Trailing Edge Serrations at Low Mach Number

Hui Tang,Yulong Lei,Yao Fu

doi:10.3390/app9183784

Abstract

Trailing-edge serrations have proven to be valid applications of trailing edge noise mitigation for an airfoil, while the physical noise reduction mechanism has not been adequately studied. We performed simulations employing Large-eddy simulation and the Lighthill–Curle method to reveal the variation in the hydrodynamic field and sound source due to the trailing edge serrations. The grid resolution and computational results were validated against experimental data. The simulation results show that: the trailing edge serrations impede the growth of spanwise vortices and promote the development of streamwise vortices near the trailing edge and the wake; the velocity fluctuations in the vertical cross-section of the streamwise direction near the trailing edge are reduced for the serrated airfoil, thereby obviously reducing the strength of the pressure fluctuations near the trailing edge; and the trailing edge serrations decrease the distribution of the sound source near the trailing edge and reduce the local peak value of sound pressure level in a specific frequency range as well as the overall sound pressure level. Moreover, we observed that, in the flow around the NACA0012 airfoil, the location where the strong sound source distribution begins to appear is in good agreement with the location where the separated boundary layer reattaches. It is therefore effective to reduce trailing edge noise by applying serrations on the upstream of the reattachment point.

Highlights

In recent years, with the development of civil aviation and the increasing popularity of air travel, the number of airports close to the city limits has grown rapidly
The weak compressibility at low Mach number was taken into account by modifying the pressure equation
It is confirmed that the growth of the spanwise vortices near the trailing edge is impeded by the trailing edge serration, and the main flow direction vortex is formed and developed from near the trailing edge to the wake for the flow field around the serrated airfoil

Summary

Introduction

With the development of civil aviation and the increasing popularity of air travel, the number of airports close to the city limits has grown rapidly. Engine jet noise used to be the major noise source for a civil aircraft, while, with the introduction of turbofan engines with high by-pass ratios, significant reductions of jet noise have been achieved. Nowadays, the reduction of the airfoil self-noise from the engine fan and airframe’s high lift devices has become more significant. Another industrial application in which the airfoil self-noise is one of the dominant noise sources is the wind turbine. For the aero-engine, airframe, and wind turbine industries, it is significant to reduce the airfoil self-noise [5,6]

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Methods

Conclusion