scholarly journals Statistical-empirical modelling of aerofoil noise subjected to leading edge serrations and aerodynamic identification of noise reduction mechanisms

2016 ◽  
Author(s):  
Till Biedermann ◽  
Tze Pei Chong ◽  
Frank Kameier
Keyword(s):  
Noise Reduction ◽  
Leading Edge ◽  
Empirical Modelling ◽  
Reduction Mechanisms

Noise reduction mechanisms for the inclined leading edge vaned diffuser in a centrifugal fan

2017 ◽  
Vol 231 (1) ◽  
pp. 68-83 ◽  
Author(s):  
Gong Wu Qi ◽  
Zhang Wei
Keyword(s):  
Noise Reduction ◽  
Pressure Fluctuation ◽  
Numerical Study ◽  
Second Harmonic ◽  
Leading Edge ◽  
Centrifugal Fan ◽  
Fan Noise ◽  
Vaned Diffuser ◽  
Reduction Mechanisms ◽  
Centrifugal Fans

An experimental and numerical study to explore the noise reduction mechanism for the inclined leading edge vaned diffuser in centrifugal fans is described. Inclined leading edge vaned diffuser is useful in improving fan performance, increasing operating range, and reducing fan noise. The generation of fan noise is related to the pressure fluctuation on the diffuser vane surface, particularly the leading edge. Numerical results show that pressure fluctuation on the inclined leading edge vaned diffuser surface remarkably decreases, unlike that of the original diffuser. The pressure fluctuation is dominated by the components at the blade passing frequency and its second harmonic.

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.

Spanwise varying porosity for the enhancement of leading-edge noise reduction

2021 ◽  
Author(s):  
Lorna J. Ayton ◽  
Orestis Karapiperis ◽  
Manuj Awasthi ◽  
Danielle Moreau ◽  
Con J. Doolan
Keyword(s):  
Noise Reduction ◽  
Leading Edge

A Study on the Fan Tone Noise Reduction with Wavy Leading Edge OGV

2021 ◽  
Author(s):  
Hang Tong ◽  
Kangshen Xiang ◽  
Liangji Zhang ◽  
Lin Li ◽  
Weijie Chen ◽  
...  
Keyword(s):  
Noise Reduction ◽  
Leading Edge

Research on the Noise Reduction and Efficiency Increase for Axial Fan with Wave Leading Edge Blades

2020 ◽  
Author(s):  
Bo Li ◽  
Yujing Wu ◽  
Dange Guo ◽  
Dan Luo ◽  
Diangui HUANG
Keyword(s):  
Noise Reduction ◽  
Sound Pressure Level ◽  
Wave Amplitude ◽  
Sound Pressure ◽  
Noise Analysis ◽  
Leading Edge ◽  
Pressure Level ◽  
Wave Number ◽  
Monitoring Point ◽  
Reduction Effect

Abstract This paper imitates the raised structure of the leading edge of the humpback whale fin limbs, designed six bionic blades. The aerodynamic analysis show that: the wave leading edge blade can improve the total pressure efficiency of the axial flow fan, and under off-design conditions, the aerodynamic performance of bionic fan is better than that of prototype fan. The noise analysis shows that: under the condition of constant wave number, increasing wave amplitude can reduce the overall sound pressure level at the monitoring point, in the middle and high frequency range, the sound pressure level of the bionic fan at the monitoring point is significantly lower than that of the prototype fan, and the noise reduction effect increases with the increase of wave amplitude; under the condition of constant wave amplitude, increasing the wave number can reduce the fan noise. At a certain wave number and amplitude, the overall sound pressure level of the bionic fan at the monitoring point is at most 2.91 dB lower than that of the prototype fan. In this paper, the noise reduction effect of increasing wave number is more obvious than that of increasing wave amplitude.

scholarly journals An analytical and experimental investigation of aerofoil–turbulence interaction noise for plates with spanwise-varying leading edges

2019 ◽  
Vol 865 ◽  
pp. 137-168 ◽  
Author(s):  
Lorna J. Ayton ◽  
Paruchuri Chaitanya
Keyword(s):  
Noise Reduction ◽  
Analytic Solution ◽  
Piecewise Linear ◽  
Separation Of Variables ◽  
Leading Edge ◽  
Test Case ◽  
Far Field ◽  
Mean Flow ◽  
Flat Plates ◽  
Leading Edges

This paper presents an analytic solution for gust–aerofoil interaction noise for flat plates with spanwise-varying periodic leading edges in uniform mean flow. The solution is obtained by solving the linear inviscid equations via separation of variables and the Wiener–Hopf technique, and is suitable for calculating the far-field noise generated by any leading edge with a single-valued piecewise linear periodic spanwise geometry. Acoustic results for homogeneous isotropic turbulent flow are calculated by integrating the single-gust solution over a wavenumber spectrum. The far-sound pressure level is calculated for five test-case geometries; sawtooth serration, slitted $v$-root, slitted $u$-root, chopped peak and square wave, and compared to experimental measurements. Good agreement is seen over a range of frequencies and tip-to-root ratios (varying the sharpness of the serration). The analytic solution is then used to calculate the propagating pressure along the leading edge of the serration for fixed spanwise wavenumbers, i.e. only the contribution to the surface pressure which propagates to the far field. Using these results, two primary mechanisms for noise reduction are discussed; tip and root interference, and a redistribution of energy from cuton modes to cutoff modes. A secondary noise-reduction mechanism due to nonlinear features is also discussed and seen to be particularly important for leading edges with very narrow slits.

scholarly journals Numerical analysis of broadband noise reduction with wavy leading edge

2018 ◽  
Vol 31 (7) ◽  
pp. 1489-1505 ◽  
Author(s):  
Fan TONG ◽  
Weiyang QIAO ◽  
Weijie CHEN ◽  
Haoyi CHENG ◽  
Renke WEI ◽  
...  
Keyword(s):  
Numerical Analysis ◽  
Noise Reduction ◽  
Leading Edge ◽  
Broadband Noise

Successive Aeroacoustic Transfer of Leading Edge Serrations From Single Airfoil to Low-Pressure Fan Application

2019 ◽  
Vol 141 (10) ◽  
Author(s):  
Till M. Biedermann ◽  
F. Kameier ◽  
C. O. Paschereit
Keyword(s):  
Noise Reduction ◽  
Pressure Fluctuations ◽  
Leading Edge ◽  
Broadband Noise ◽  
Rotating Frame ◽  
Continuous Increase ◽  
Stall Margin ◽  
Wall Pressure Fluctuations ◽  
Turbulent Inflow ◽  
Fan Blade

Abstract Leading edge serrations are identified as an effective passive treatment for reducing fan broadband noise due to high turbulent inflow conditions. This paper aims to investigate the isolated effect of serrated applications in a rotating frame, covering the aerodynamic and aeroacoustic performance. With this purpose, a serration design, previously analyzed in the rigid domain, is transferred to the rotating frame, following a successive approach in form of a continuous increase of the fan blade number. This is considered as a feasible way to isolate the serration effects and to provide information on fan blade interaction and possible masking effects. Comparing blades with straight and serrated leading edges by analyzing the spectral noise reduction and the overall level result in deep insights in the underlying noise reduction mechanisms. Furthermore, analysis of phase differences by means of the wall pressure fluctuations leads to the identification of rotating flow phenomena, nonsynchronized with the rotor speed. The results obtained indicate an efficient noise reduction by the serrations in the vicinity of the design point. By use of the presented successive approach, noise reduction phenomena observed with the full rotor could be identified to be of either aeroacoustic or aerodynamic nature. A reduced noise is observed for the full rotor case, showing a reduction of blade interaction effects. At reducing flow coefficients, an improved stall margin of the serrated rotor is identified that also affects the aeroacoustic signature.

Hydrofoil vibration and noise reduction with leading edge isolation

2005 ◽  
Vol 118 (3) ◽  
pp. 1951-1951
Author(s):  
Timothy A. Brungart ◽  
Eric C. Myer ◽  
Dean E. Capone ◽  
Robert L. Campbell
Keyword(s):  
Noise Reduction ◽  
Leading Edge

On the reductions of aerofoil-turbulence interaction noise through multi-wavelength leading edge serrations

2020 ◽  
pp. 095441002096574
Author(s):  
S Narayanan ◽  
Sushil Kumar Singh
Keyword(s):  
Noise Reduction ◽  
Maximum Amplitude ◽  
Leading Edge ◽  
Emission Angle ◽  
Broadband Noise ◽  
Dual Wavelength ◽  
Flat Plates ◽  
Wide Range ◽  
Multi Wavelength ◽  
Reduction Characteristics

This paper provides an experimental study into the use of multi-wavelength sinusoidal leading edge ( LE) serrations for enhancing the aerofoil-broadband noise reductions. The noise reduction performances of multi-wavelength serration profiles introduced on a flat plate are compared against those generated by single-wavelength profiles when applied separately. The multi-wavelength leading edge serration is made in such a way that its maximum amplitude is kept same as that of each single-wavelength ones to be compared. The present study reveals that the dual-wavelength serrations provide higher noise reductions over a narrow band of frequencies as compared to single and triple wavelength ones. Further, it reveals that the noise reduction characteristics of dual-wavelength serrated airfoils are similar to the flat plates. It shows that the baseline plate generate higher noise radiations for all emission angles as compared to leading edge serrated plates, but the common feature among them is the downstream directivity. For the range of frequencies 0.9 to 5 kHz, the highest directivity is seen at an emission angle of 55° for the baseline, while it occurs at 75° for the serrated plates. The dual wavelength serrations generate lowest acoustic radiations as compared to single and triple ones for all the emission angles. Also, it is noticed that the radiation levels of the dual serrations decrease with increase in amplitude of the serration, which shows that the longer dual serrations generate lowest acoustic radiations. Thus, the present study illustrates that the dual wavelength leading edge serrations act as the best passively modified serration profiles for achieving the highest noise reductions over a wide range of frequencies as compared to single and triple wavelength ones.

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