scholarly journals Bio-Inspired Aerodynamic Noise Control: A Bibliographic Review

2019 ◽  
Vol 9 (11) ◽  
pp. 2224 ◽  
Author(s):  
Yong Wang ◽  
Kun Zhao ◽  
Xiang-Yu Lu ◽  
Yu-Bao Song ◽  
Gareth J. Bennett
Keyword(s):  
Noise Reduction ◽  
Noise Control ◽  
Experimental Studies ◽  
Morphological Characteristics ◽  
Leading Edge ◽  
Aerodynamic Noise ◽  
Trailing Edge ◽  
Reduction Techniques ◽  
Noise Measurements ◽  
Underlying Mechanisms

It is well-known that many species of owl have the unique ability to fly silently, which can be attributed to their distinctive and special feather adaptations. Inspired by the owls, researchers attempted to reduce the aerodynamic noise of aircraft and other structures by learning their noise reduction features from different viewpoints and then using the gained knowledge to develop a number of innovative noise reduction solutions. Although fruitful results have been achieved in the bio-inspired aerodynamic noise control, as far as the authors know, comparatively little work has been done to summarize the main findings and progresses in this area. In this bibliographic survey, we systematically review the progresses and trends of the bio-inspired aerodynamic noise control, including the macroscopic and microscopic morphological characteristics of the owl wing feathers, the noise measurements on both flying birds in the field and prepared wings in the wind tunnel, as well as theoretical, numerical and experimental studies that explored the feasibility, parameter influence, aerodynamic effects and underlying mechanisms of the four main bio-inspired noise reduction techniques, i.e., leading edge serrations, trailing edge serrations, fringe-type trailing edge extensions and porous material inspired noise reduction. Finally, we also give some suggestions for future work.

A BRIEF REVIEW ON VARIOUS NOISE REDUCTION TECHNIQUES EMANATING FROM WINGS OF AN AIRCRAFT

2021 ◽  
Vol 6 (3) ◽  
Author(s):  
Oyeniran Noah D
Keyword(s):  
Noise Reduction ◽  
Leading Edge ◽  
Aerodynamic Noise ◽  
Aviation Industry ◽  
Noise Emission ◽  
Reduction Techniques ◽  
High Level ◽  
Work Done ◽  
Active Flow ◽  
Sharp Leading Edge

— One of the challenges and a point of need in the aviation industry is the problem of high level of noise emanation. There are various sources of noise emanating from aircraft which are the noises from engine and airframe including the wings. Noise from the wing is an important phenomenon to be put into consideration as it contributes significantly to the noise emanating from aircraft especially during take-off and landing. Airfoil noise emission emanate on the wing section of an aircraft due to the interaction of the airfoil turbulent boundary layer with the sharp leading edge. Noise reduction then becomes a thing of concern for many engineers and researchers who took it upon their shoulder the responsibility of coming up with design that can help reduce noise emanating from aircrafts to mitigate the noise. Due to this, many researchers have focused on reducing the noise emanating from the aircraft through various means and approaches which include theoretical, computational, and experimental analysis. In a means of compiling and making available a brief review of such work, for easy and quick access necessitate the need of this work. This paper focused on giving a summary and review of different work done by past and current researchers in the field. The review was based on selected current papers on the cutting-edge technology towards enhancing aerodynamic performance of the wing of aircraft and reduction of noise emanating from it. Although fruitful results have been achieved in the aerodynamic noise control, but only little work has been done to summarize the main findings and progresses in this area. This work focused on review of work carried out by many researchers in this area which involves various techniques and attempts ranging from leading edge serration, trailing edge serration, active flow actuation, flexible wing using theoretical, computational, and experimental approach etc. Additionally, some suggestions were made towards further study and improv

scholarly journals The Application of a Linear Microphone Array in the Quantitative Evaluation of the Blade Trailing-Edge Noise Reduction

2021 ◽  
Vol 11 (2) ◽  
pp. 572
Author(s):  
Weijie Chen ◽  
Luqin Mao ◽  
Kangshen Xiang ◽  
Fan Tong ◽  
Weiyang Qiao
Keyword(s):  
Noise Reduction ◽  
Quantitative Evaluation ◽  
Microphone Array ◽  
Experimental Studies ◽  
Flow Speed ◽  
Aerodynamic Noise ◽  
Noise Sources ◽  
Trailing Edge ◽  
Array Data ◽  
Clean Algorithm

This paper concerns the application of a linear microphone array in the quantitative evaluation of blade trailing-edge (TE) noise reduction. The noise radiation from the blades with straight and serrated TEs is measured in an indoor open-jet wind tunnel. The array data are processed using the inverse method based on the Clean algorithm based on spatial source coherence (Clean-SC). In order to obtain correct application and achieve the best effect for the microphone array test, the computing software for array data reduction is firstly developed and assessed by Sarradj’s benchmark case. The assessment results show that the present array data processing method has a good accuracy with an error less than 0.5 dB in a wide frequency range. Then, a linear array with 32 microphones is designed to identify the noise source of a NACA65(12)-10 blade. The performance of the Clean-SC algorithm is compared with the Clean algorithm based on point spread functions (Clean-PSF) method for experimentally identifying the noise sources of the blade. The results show that there is about a 2 dB error when using the Clean-PSF algorithm due to the interference of different aerodynamic noise sources. Experimental studies are conducted to study the blade TE noise reduction using serrated TEs. The TE noise for the blade with and without sawtooth configurations is measured with the flow speeds from 20 m/s to 70 m/s, and the corresponding Reynolds numbers based on the chord are from 200,000 to 700,000. Parametric studies of the sawtooth amplitude and wavelength are conducted to understand the noise reduction law. It is observed that the TE noise reduction is sensitive to both the amplitude and wavelength. The flow speed also affects the noise reduction in the serrated TEs. To obtain the best noise suppression effect, the sawtooth configuration should be carefully designed according to the actual working conditions and airflow parameters.

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.

scholarly journals Aeroacoustics of Silent Owl Flight

2020 ◽  
Vol 52 (1) ◽  
pp. 395-420 ◽  
Author(s):  
Justin W. Jaworski ◽  
N. Peake
Keyword(s):  
Mathematical Modeling ◽  
Noise Reduction ◽  
Current Knowledge ◽  
Foraging Strategies ◽  
Aerodynamic Noise ◽  
Noise Generation ◽  
Reduction Strategies ◽  
Noise Measurements ◽  
Modeling And Experiments ◽  
Review Current

The ability of some species of owl to fly in effective silence is unique among birds and provides a distinct hunting advantage, but it remains a mystery as to exactly what aspects of the owl and its flight are responsible for this dramatic noise reduction. Crucially, this mystery extends to how the flow physics may be leveraged to generate noise-reduction strategies for wider technological application. We review current knowledge of aerodynamic noise from owls, ranging from live owl noise measurements to mathematical modeling and experiments focused on how owls may disrupt the standard routes of noise generation. Specialized adaptations and foraging strategies are not uniform across all owl species: Some species may not have need for silent flight, or their evolutionary adaptations may not be effective for useful noise reduction for certain species. This hypothesis is examined using mathematical models and borne out where possible by noise measurements and morphological observations of owl feathers and wings.

Experimental Study of Aerodynamic Noise From the Trailing Edge and Leading Edge of Blades in a Coaxial-Double Shaft Fan

2013 ◽  
Author(s):  
Jafar Madadnia ◽  
Mustafa Shekeb ◽  
Thimantha Ulluwishewa
Keyword(s):  
Wind Turbines ◽  
Acoustic Noise ◽  
Residential Building ◽  
Leading Edge ◽  
Noise Pollution ◽  
Aerodynamic Noise ◽  
Trailing Edge ◽  
Double Row ◽  
Positive Effects ◽  
Spacing Variation

Proactive acoustic noise control technologies in wind turbines and blowers have in recent years been the focus of intensive research to integrate wind turbines in residential building and to address public concerns on noise pollution. However efforts to understand the mechanics has been inconclusive, mainly due to the complexity and commercial confidentiality of the topic. The paper reports on the experimental investigation on two methods in controlling aerodynamic noise. A counter-rotating-double-row-turbine with variable gap/spacing (s) was designed, built and tested. Serrations were designed and attached on the leading edge and the trailing edge of the blades to proactively control aerodynamic noise. The model was operated in fan-mode and air velocity, shaft-revolution; electric-fan-power, acoustic noise amplitude (dB) and Centre frequency (CF in Hz) were measured for a number of spacing and serrations. Coefficients of Performance (COP), dB, CF were plotted against tip speed (TS). It was noticed that: • The double-shaft-fan has operated quieter than the single shaft fan especially as TS decreases. Acoustic noise (dB) dropped 20% at TS = 4m/s to less than 2% at TS = 10m/s. Efficiency and CF increased in the double-shaft fan as TS increased. Spacing variation between blade-rows had insignificant effect on the dB, Cf, and efficiency. • Serrations on single-shaft fan have also reduced dB (up to 10%), increased efficiency and CF with more positive effects with the serrations on the leading edge than the trailing edge. Serrations are more effective at higher TS range. • Serrations on a double-shaft fan with an optimum spacing, reduced acoustic noise (dB) only allow speeds [at TS <4m/s]. However minor improvement was noticed in efficiency or noise frequency.

scholarly journals Features of owl wings that promote silent flight

2017 ◽  
Vol 7 (1) ◽  
pp. 20160078 ◽  
Author(s):  
Hermann Wagner ◽  
Matthias Weger ◽  
Michael Klaas ◽  
Wolfgang Schröder
Keyword(s):  
Noise Reduction ◽  
Leading Edge ◽  
Aerodynamic Performance ◽  
Wing Loading ◽  
Trailing Edge ◽  
Future Directions ◽  
Trailing Edge Noise ◽  
Aerodynamic Properties ◽  
Morphological Adaptations ◽  
Noise Production

Owls are an order of birds of prey that are known for the development of a silent flight. We review here the morphological adaptations of owls leading to silent flight and discuss also aerodynamic properties of owl wings. We start with early observations (until 2005), and then turn to recent advances. The large wings of these birds, resulting in low wing loading and a low aspect ratio, contribute to noise reduction by allowing slow flight. The serrations on the leading edge of the wing and the velvet-like surface have an effect on noise reduction and also lead to an improvement of aerodynamic performance. The fringes at the inner feather vanes reduce noise by gliding into the grooves at the lower wing surface that are formed by barb shafts. The fringed trailing edge of the wing has been shown to reduce trailing edge noise. These adaptations to silent flight have been an inspiration for biologists and engineers for the development of devices with reduced noise production. Today several biomimetic applications such as a serrated pantograph or a fringed ventilator are available. Finally, we discuss unresolved questions and possible future directions.

scholarly journals Prediction of noise from serrated trailing edges

2016 ◽  
Vol 793 ◽  
pp. 556-588 ◽  
Author(s):  
B. Lyu ◽  
M. Azarpeyvand ◽  
S. Sinayoko
Keyword(s):  
Noise Reduction ◽  
Analytical Model ◽  
Leading Edge ◽  
Experimental Investigations ◽  
Destructive Interference ◽  
Trailing Edge ◽  
Trailing Edges ◽  
Mach Numbers ◽  
Trailing Edge Serrations ◽  
High Mach

A new analytical model is developed for the prediction of noise from serrated trailing edges. The model generalizes Amiet’s trailing-edge noise theory to sawtooth trailing edges, resulting in a complicated partial differential equation. The equation is then solved by means of a Fourier expansion technique combined with an iterative procedure. The solution is validated through comparison with the finite element method for a variety of serrations at different Mach numbers. The results obtained using the new model predict noise reduction of up to 10 dB at 90$^{\circ }$ above the trailing edge, which is more realistic than predictions based on Howe’s model and also more consistent with experimental observations. A thorough analytical and numerical analysis of the physical mechanism is carried out and suggests that the noise reduction due to serration originates primarily from interference effects near the trailing edge. A closer inspection of the proposed mathematical model has led to the development of two criteria for the effectiveness of the trailing-edge serrations, consistent but more general than those proposed by Howe. While experimental investigations often focus on noise reduction at 90$^{\circ }$ above the trailing edge, the new analytical model shows that the destructive interference scattering effects due to the serrations cause significant noise reduction at large polar angles, near the leading edge. It has also been observed that serrations can significantly change the directivity characteristics of the aerofoil at high frequencies and even lead to noise increase at high Mach numbers.

The generation of sound in turbulent motion

2008 ◽  
Vol 112 (1133) ◽  
pp. 381-394 ◽  
Author(s):  
G. M. Lilley
Keyword(s):  
Noise Reduction ◽  
Turbulent Flows ◽  
High Speed ◽  
Experimental Studies ◽  
Supersonic Jet ◽  
Jet Noise ◽  
Aerodynamic Noise ◽  
Turbulent Shear ◽  
Noise Generation ◽  
Physical Mechanisms

Abstract The present paper reviews and discusses the physical mechanisms of noise generation and reduction in turbulent flows with their applications towards aircraft noise reduction at takeoff and on the approach. This work began in 1948 when Lilley undertook an experimental investigation into the source of jet noise as a necessary precursor to finding methods for the reduction of high speed jet engine noise on civil jet airliners. Westley and Lilley completed this experimental programme in 1951, which included the design of a range of devices for high speed jet noise reduction. It was about this time that similar studies on jet noise were being started elsewhere and in particular by Lassiter and Hubbard in USA. The major contribution to the subject of turbulence as a source of noise came from Sir James Lighthill’s remarkable theory in 1952. In spite of the difficulties attached to theoretical and experimental studies on noise from turbulence, it is shown that with the accumulated knowledge on aerodynamic noise over the past 50 years, together with an optimisation of aircraft operations including flight trajectories, we are today on the threshold of approaching the design of commercial aircraft with turbofan propulsion engines that will not be heard above the background noise of the airport at takeoff and landing beyond 1-2km, from the airport boundary fence. It is evident that in the application of this work, which centres on the physical mechanisms relating to the generation of noise from turbulence and turbulent shear flows, to jet noise, there is not one unique mechanism of jet noise generation for all jet Mach numbers. This author in this publication has concentrated on what appears to be the dominant mechanism of noise generation from turbulence, where the mean convection speeds of the turbulence are subsonic. The noise generated at transonic and supersonic jet speeds invariably involves extra mechanisms, which are only briefly referred to here.

scholarly journals Acoustic scattering by a finite rigid plate with a poroelastic extension

2016 ◽  
Vol 791 ◽  
pp. 414-438 ◽  
Author(s):  
Lorna J. Ayton
Keyword(s):  
Noise Reduction ◽  
Acoustic Field ◽  
Wind Turbines ◽  
Acoustic Scattering ◽  
Leading Edge ◽  
Chord Length ◽  
Far Field ◽  
Rigid Plate ◽  
Acoustic Source ◽  
Trailing Edge

The scattering of sound by a finite rigid plate with a finite poroelastic extension interacting with an unsteady acoustic source is investigated to determine the effects of porosity, elasticity and the length of the extension when compared to a purely rigid plate. The problem is solved using the Wiener–Hopf technique, and an approximate Wiener–Hopf factorisation process is implemented to yield reliable far-field results quickly. Importantly, finite chord-length effects are taken into account, principally the interaction of a rigid leading-edge acoustic field with a poroelastic trailing-edge acoustic field. The model presented discusses how the poroelastic trailing-edge property of owls’ wings could inspire quieter aeroacoustic designs in bladed systems such as wind turbines, and provides a framework for analysing the potential noise reduction of these designs.

Sign in / Sign up

Export Citation Format

Share Document