On the Reductions of Airfoil Broadband Noise through Sinusoidal Trailing-Edge Serrations

A detailed experimental study is conducted to observe the effect of various parameters like wavelength, depth of serrations, and pitch angle on serrated blades' acoustic emissions at low speeds up to 2000 rpm. Experiments are conducted on flat blade rotors with sinusoidal serrations on the trailing edge of blades with different amplitudes and wavelengths. A total of 7 blades with different serration configurations, including a base configuration, are studied, five of them have serrations throughout the span of the blade, and one configuration has serration of varying amplitude on the farther half of the blade. It is observed that some blade configurations have resulted in tonal noise reduction noise as much as 8dB, whereas some of the serration configurations reduce very little to none, there is no significant effect of T.E serrations on the broadband noise emitted by the rotor. Directivity of noise generated from the rotor, the effect of serrations on the directivity of the noise is studied.

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Broadband Noise Reduction Of Linear Cascades With Trailing Edge Serrations

17th AIAA/CEAS Aeroacoustics Conference (32nd AIAA Aeroacoustics Conference) ◽

10.2514/6.2011-2874 ◽

2011 ◽

Cited By ~ 13

Author(s):

Arthur Finez ◽

Marc Jacob ◽

Michel Roger ◽

Emmanuel Jondeau

Keyword(s):

Noise Reduction ◽

Broadband Noise ◽

Trailing Edge ◽

Trailing Edge Serrations

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Optimization of trailing-edge serrations with and without slits for broadband noise reduction

Journal of Sound and Vibration ◽

10.1016/j.jsv.2020.115736 ◽

2021 ◽

Vol 490 ◽

pp. 115736

Author(s):

Pavel Kholodov ◽

Stéphane Moreau

Keyword(s):

Noise Reduction ◽

Broadband Noise ◽

Trailing Edge ◽

Trailing Edge Serrations

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Numerical study of optimized airfoil trailing-edge serrations for broadband noise reduction

AIAA AVIATION 2020 FORUM ◽

10.2514/6.2020-2541 ◽

2020 ◽

Author(s):

Pavel Kholodov ◽

Stephane Moreau

Keyword(s):

Noise Reduction ◽

Numerical Study ◽

Broadband Noise ◽

Trailing Edge ◽

Trailing Edge Serrations

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Experimental Study on the Turbomachinery Trailing Edge Noise Reduction

Volume 2A: Turbomachinery ◽

10.1115/gt2016-56453 ◽

2016 ◽

Author(s):

Fan Tong ◽

Wei-Yang Qiao ◽

Liang Ji ◽

Kun-Bo Xu ◽

Xun-Nian Wang

Keyword(s):

Noise Reduction ◽

Wide Frequency Range ◽

Broadband Noise ◽

Special Focus ◽

Turbine Cascade ◽

Frequency Range ◽

Trailing Edge ◽

Trailing Edge Noise ◽

Reduction Effect ◽

Trailing Edge Serrations

This paper is a continuation of a series of study on the mechanism of the broadband noise reduction for turbomachinery blade using trailing edge serrations. The noise reduction potential of turbine blade with trailing edge serrations is experimentally assessed as well as the various parameters on the noise reduction effect. Special focus is put on whether the trailing edge serrations affect turbine cascade tailing edge noise in the same way as they do on the isolated airfoil. Five different trailing edge serrations were designed for a turbine linear cascade to investigate the effects of serration geometry parameter on the noise reduction. A linear microphone array was used to quantify the difference of sound source levels of turbine cascade with and without trailing edge modifications. The experiment was carried out at various velocities and the Reynolds number (based on cascade inlet velocity and chord) ranges from 1.3×105 to 3.3×105. The experiment results show that trailing edge serrations can reduce turbine trailing edge noise in a wide frequency range that we are interested (from 1600Hz to 10000Hz) and a maximum noise reduction of about 5dB is obtained in the mid frequency range (2000Hz to 4000Hz). The results show that the serration length has an important effect on the noise reduction effect and the longer serration in the experiment lead to more noise reduction. However, serration wavelength has only a little effect on the noise reduction although the wider trailing edge serrations tested in the experiment can achieve slightly more noise reduction. This is quite different from that for airfoils. At all the velocities tested, the cascade trailing edge noise is effectively reduced and the maximum noise reduction occurs at St=2fh/U≈1.

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Numerical study on the airfoil self-noise of three owl-based wings with the trailing-edge serrations

Proceedings of the Institution of Mechanical Engineers Part G Journal of Aerospace Engineering ◽

10.1177/0954410020988229 ◽

2021 ◽

pp. 095441002098822

Author(s):

Dian Li ◽

Xiaomin Liu ◽

Lei Wang ◽

Fujia Hu ◽

Guang Xi

Keyword(s):

Flow Field ◽

Noise Reduction ◽

Numerical Study ◽

Barn Owl ◽

Aerodynamic Noise ◽

Frequency Noise ◽

Trailing Edge ◽

Reduction Mechanisms ◽

Trailing Edge Serrations ◽

Bionic Airfoil

Previous publications have summarized that three special morphological structures of owl wing could reduce aerodynamic noise under low Reynolds number flows effectively. However, the coupling noise-reduction mechanism of bionic airfoil with trailing-edge serrations is poorly understood. Furthermore, while the bionic airfoil extracted from natural owl wing shows remarkable noise-reduction characteristics, the shape of the owl-based airfoils reconstructed by different researchers has some differences, which leads to diversity in the potential noise-reduction mechanisms. In this article, three kinds of owl-based airfoils with trailing-edge serrations are investigated to reveal the potential noise-reduction mechanisms, and a clean airfoil based on barn owl is utilized as a reference to make a comparison. The instantaneous flow field and sound field around the three-dimensional serrated airfoils are simulated by using incompressible large eddy simulation coupled with the FW-H equation. The results of unsteady flow field show that the flow field of Owl B exhibits stronger and wider-scale turbulent velocity fluctuation than that of other airfoils, which may be the potential reason for the greater noise generation of Owl B. The scale and magnitude of alternating mean convective velocity distribution dominates the noise-reduction effect of trailing-edge serrations. The noise-reduction characteristic of Owl C outperforms that of Barn owl, which suggests that the trailing-edge serrations can suppress vortex shedding noise of flow field effectively. The trailing-edge serrations mainly suppress the low-frequency noise of the airfoil. The trailing-edge serration can suppress turbulent noise by weakening pressure fluctuation.

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Surface roughness effect on rotor broadband noise

International Journal of Aeroacoustics ◽

10.1177/1475472x18778278 ◽

2018 ◽

Vol 17 (4-5) ◽

pp. 438-466 ◽

Cited By ~ 2

Author(s):

Baofeng Cheng ◽

Yiqiang Han ◽

Kenneth S Brentner ◽

Jose Palacios ◽

Philip J Morris ◽

...

Keyword(s):

Boundary Layer ◽

Surface Roughness ◽

Turbulent Boundary Layer ◽

Layer Thickness ◽

Turbulence Intensity ◽

Boundary Layer Thickness ◽

Broadband Noise ◽

Ice Accretion ◽

Trailing Edge ◽

Trailing Edge Noise

The change of helicopter rotor broadband noise due to different surface roughness during ice accretion is investigated. Comprehensive rotor broadband noise measurements are carried out on rotor blades with different roughness sizes and rotation speeds in two facilities: the Adverse Environment Rotor Test Stand facility at The Pennsylvania State University, and the University of Maryland Acoustic Chamber. In both facilities, the measured high-frequency broadband noise increases significantly with increasing surface roughness height. Rotor broadband noise source identification is conducted and the broadband noise related to ice accretion is thought to be turbulent boundary layer-trailing edge noise. Theory suggests turbulent boundary layer-trailing edge noise scales with Mach number to the fifth power, which is also observed in the experimental data confirming that the dominant broadband noise mechanism during ice accretion is trailing edge noise. A correlation between the ice-induced surface roughness and the broadband noise level is developed. The correlation is strong, which can be used as an ice accretion early detection tool for helicopters, as well as to quantify the ice-induced roughness at the early stage of rotor ice accretion. The trailing edge noise theories developed by Ffowcs Williams and Hall, and Howe both identify two important parameters: boundary layer thickness and turbulence intensity. Numerical studies of two-dimensional airfoils with different ice-induced surface roughness heights are conducted to investigate the extent that surface roughness impacts the boundary layer thickness and turbulence intensity (and ultimately the turbulent boundary layer-trailing edge noise). The results show that boundary layer thickness and turbulence intensity at the trailing edge increase with the increased roughness height. Using Howe’s trailing edge noise model, the increased sound pressure level of the trailing edge noise due to the increased displacement thickness and normalized integrated turbulence intensity are 6.2 and 1.6 dB for large and small accreted ice roughness heights, respectively. The estimated increased sound pressure level values agree reasonably well with the experimental results, which are 5.8 and 2.6 dB for large and small roughness height, respectively.

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