Permeable Leading Edges for Airfoil and Fan Noise Reduction in Disturbed Inflow

AIAA Journal ◽  
2021 ◽  
pp. 1-18
Author(s):  
Christof Ocker ◽  
Thomas F. Geyer ◽  
Felix Czwielong ◽  
Florian Krömer ◽  
Wolfram Pannert ◽  
...  
Keyword(s):  
Noise Reduction ◽  
Fan Noise ◽  
Leading Edges

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.

Condenser fan noise reduction solutions

2000 ◽  
Vol 108 (5) ◽  
pp. 2461-2461
Author(s):  
Michael Bobeczko
Keyword(s):  
Noise Reduction ◽  
Fan Noise

scholarly journals On the universal trends in the noise reduction due to wavy leading edges in aerofoil–vortex interaction

2019 ◽  
Vol 871 ◽  
pp. 186-211 ◽  
Author(s):  
Jacob M. Turner ◽  
Jae Wook Kim
Keyword(s):  
Noise Reduction ◽  
High Frequency ◽  
Broadband Noise ◽  
Current Work ◽  
Source Distribution ◽  
Source Analysis ◽  
Frequency Noise ◽  
Frequency Spectra ◽  
Low Frequencies ◽  
Leading Edges

Existing studies suggest that wavy leading edges (WLEs) offer substantial reduction of broadband noise generated by an aerofoil undergoing upstream vortical disturbances. In this context, there are two universal trends in the frequency spectra of the noise reduction which have been observed and reported to date: (i) no significant reduction at low frequencies followed by (ii) a rapid growth of the noise reduction that persists in the medium-to-high frequency range. These trends are known to be insensitive to the aerofoil type and flow condition used. This paper aims to provide comprehensive understandings as to how these universal trends are formed and what the major drivers are. The current work is based on very-high-resolution numerical simulations of a semi-infinite flat-plate aerofoil impinged by a prescribed divergence-free vortex in an inviscid base flow at zero incidence angle, continued from recent work by the authors (Turner & Kim, J. Fluid Mech., vol. 811, 2017, pp. 582–611). One of the most significant findings in the current work is that the noise source distribution on the aerofoil surface becomes entirely two-dimensional (highly non-uniform in the spanwise direction as well as streamwise) at high frequencies when the WLE is involved. Also, the sources downstream of the LE make crucial contributions to creating the universal trends across all frequencies. These findings contradict the conventional LE-focused one-dimensional source analysis that has widely been accepted for all frequencies. The current study suggests that the universal trends in the noise-reduction spectra can be properly understood by taking the downstream source contributions into account, in terms of both magnitude and phase variations. After including the downstream sources, it is shown in this paper that the first universal trend is due to the conservation of total (surface integrated) source energy at low frequencies. The surface-integrated source magnitude that decreases faster with the WLE correlates very well with the noise-reduction spectrum at medium frequencies. In the meantime, the high-frequency noise reduction is driven almost entirely by destructive phase interference that increases rapidly and consistently with frequency, explaining the second universal trend.

Study of Tonal Fan Noise Reduction by Modification of the Volute Cutoff

2010 ◽  
Vol 96 (6) ◽  
pp. 1115-1124 ◽  
Author(s):  
Jiancheng Cai ◽  
Datong Qi ◽  
Fuan Lu ◽  
Xuanfeng Wen
Keyword(s):  
Noise Reduction ◽  
Fan Noise

scholarly journals Benefits of swept and leaned stators for fan noise reduction

1999 ◽  
Author(s):  
Richard Woodward ◽  
David Elliot ◽  
Christopher Hughes ◽  
Jeffrey Berton
Keyword(s):  
Noise Reduction ◽  
Fan Noise

scholarly journals Fan Noise Reduction: An Overview

2002 ◽  
Vol 1 (1) ◽  
pp. 43-64 ◽  
Author(s):  
Edmane Envia
Keyword(s):  
Noise Reduction ◽  
Fan Noise

Fan Noise Reduction with Increased Bypass Nozzle Area

2006 ◽  
Vol 43 (6) ◽  
pp. 1719-1725 ◽  
Author(s):  
Richard P. Woodward ◽  
Christopher E. Hughes ◽  
Gary G. Podboy
Keyword(s):  
Noise Reduction ◽  
Fan Noise

Fan noise reduction of household refrigerator

1992 ◽  
Vol 28 (2) ◽  
pp. 287-292 ◽  
Author(s):  
A. Takushima ◽  
Y. Shinobu ◽  
S. Tanaka ◽  
M. Eguchi ◽  
K. Matsuki
Keyword(s):  
Noise Reduction ◽  
Fan Noise
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