Broadband Noise Reduction Of Linear Cascades With Trailing Edge Serrations

2011 ◽  
Author(s):  
Arthur Finez ◽  
Marc Jacob ◽  
Michel Roger ◽  
Emmanuel Jondeau
Keyword(s):  
Noise Reduction ◽  
Broadband Noise ◽  
Trailing Edge ◽  
Trailing Edge Serrations

Experimental study of wavy trailing edge serrations on flat rotor blades

2021 ◽  
Vol 263 (5) ◽  
pp. 1855-1866
Author(s):  
Sai Manikanta Kaja ◽  
K. Sriinivasan ◽  
A. Jaswanth Kalyan Kumar
Keyword(s):  
Experimental Study ◽  
Noise Reduction ◽  
Pitch Angle ◽  
Acoustic Emissions ◽  
Broadband Noise ◽  
Rotor Blades ◽  
Tonal Noise ◽  
Trailing Edge ◽  
Low Speeds ◽  
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.

Experimental Study on the Turbomachinery Trailing Edge Noise Reduction

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.

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

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.

Numerical Analysis of an Industrial Fan Fitted With Noise Reduction Devices

2006 ◽  
Author(s):  
J. Amaral Teixeira ◽  
E. Naylor ◽  
P. C. Ivey ◽  
A. G. Sheard ◽  
I. R. Kinghorn
Keyword(s):  
Numerical Analysis ◽  
Noise Reduction ◽  
Flow Characteristics ◽  
Pressure Rise ◽  
Broadband Noise ◽  
Noise Sources ◽  
Fan Noise ◽  
Trailing Edge ◽  
Low Speed ◽  
The Individual

The reduction of noise emitted by industrial low speed cooling fans, particularly those fitted to air conditioning systems is a concern to fan manufacturers. The market for industrial low speed fans is highly competitive, with fan noise being the major differentiating factor between competing products. Noise reduction strategies are therefore implemented but these can adversely affect the fan’s pressure delivery capability. A reduction of fan speed can also lead to a reduction in fan noise but this is usually accompanied by a corresponding reduction in pressure rise and flow rate. The practical difficulties associated with maintaining fan pressure and flow characteristics while simultaneously reducing fan noise present fan manufacturers with a challenge. Traditional empirical approaches to the reduction of fan noise have almost been exhausted and no longer offer the potential to significantly reduce fan noise. The understanding of the aerodynamic mechanisms that act as broadband noise sources in low speed fans has been the subject of a considerable number of papers over many years. For most fans operating as a single blade row, the main sources of noise, other than those dependent on the incident turbulence levels, depend on the trailing edge and tip gap flow conditions. A range of strategies seeking to control the noise generated by these regions have been proposed over time by various authors and a number of these schemes have reached production status. The current paper details the numerical analysis of an industrial low speed fan, commonly used in conjunction with a cooling matrix, and which incorporates two distinct noise reduction features; trailing edge crenulations and a blade tip fence. Comparisons are carried out between various combinations of blades, with and without the individual features, and a discussion of the aerodynamics of the particular configurations is undertaken from a perspective of their noise reduction capabilities.

scholarly journals Aerofoil self-noise radiations subjected to serration flap angles

2021 ◽  
Vol 62 (7) ◽  
Author(s):  
P. C. Woodhead ◽  
T. P. Chong ◽  
P. F. Joseph ◽  
A. Vathylakis
Keyword(s):  
Noise Reduction ◽  
Flat Plate ◽  
High Frequency ◽  
Cross Flow ◽  
Broadband Noise ◽  
The Self ◽  
Spanwise Direction ◽  
Trailing Edge ◽  
Blade Loading ◽  
Loading Effect

Abstract Besides the investigation of the aeroacoustics responses of an asymmetric aerofoil subjected to serrated trailing edge flap angles from negative (flap-down) to positive (flap-up), this paper also provides a new perspective on the physical mechanisms of broadband noise reduction by a serrated trailing edge. The blade-loading effect, which is a function of the length and flap angle for a straight/non-serrated trailing edge flat plate, plays a considerable role in the self-noise radiation that is hitherto less recognised. When the same trailing edge flat plate is cut into a sawtooth serration shape, the self-noise reduction will be underpinned simultaneously by both the serration effect (dominant) and the blade-loading effect. The results demonstrate that the far-field radiation of a serrated aerofoil can be manipulated significantly depending on the direction of the flap angle. In the flap-down configuration, the blade-loading will become a negative factor that causes a deterioration of the noise reduction performance across the entire frequency range. In the flap-up configuration, three spectral frequencies zones can be defined. At the low-frequency zone, the diminished cross-flow at the sawtooth gaps will impede the noise reduction capability. At the central-frequency zone, the re-distribution of the turbulence sources and reduction in the turbulence spanwise length scales will enhance the noise reduction performance. Improvement in the noise performance can also be achieved at the high-frequency zone owing to the lack of interaction between the cross-flow and sawtooth structure. A new concept is positively demonstrated by varying the serration flap angle as a periodic function across the spanwise direction (spanwise wavy serration). When compared to a non-flap serrated trailing edge, the spanwise wavy serration is found to further increase the noise reduction level between the central and high-frequency regions. Graphic abstract

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