scholarly journals Self Noise Reduction and Aerodynamics of Airfoils With Porous Trailing Edges

Acoustics ◽  
2019 ◽  
Vol 1 (2) ◽  
pp. 393-409 ◽  
Author(s):  
Thomas Fritz Geyer ◽  
Ennes Sarradj
Keyword(s):  
Porous Material ◽  
Porous Materials ◽  
Microphone Array ◽  
Aerodynamic Performance ◽  
Aerodynamic Noise ◽  
Trailing Edge ◽  
Suitable Material ◽  
Trailing Edge Noise ◽  
Negative Effect ◽  
Noticeable Reduction

The application of open-porous materials is a possible method to effectively reduce the aerodynamic noise of an airfoil. However, the porous consistency may have a negative effect on the aerodynamic performance of the airfoil, since very often the lift is decreased while the drag increases. In a recent investigation, the generation of trailing edge noise of a set of airfoil models made from different porous materials was examined experimentally. The materials were characterized mainly by their airflow resistivity. Besides the material, the chordwise extent of the porous material was varied, which was done by covering the front part of the porous airfoil with a thin, impermeable adhesive foil. Acoustic measurements were performed in an open jet wind tunnel using microphone array technology, while the aerodynamic performance was measured simultaneously using a six-component balance. In general, both the airflow resistivity and the extent of the porous material have an influence on the trailing edge noise. However, if a suitable material is chosen, the results show that a noticeable reduction of trailing edge noise is possible even with only a small chordwise extent of the porous material.

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 Numerical investigation of porous materials for trailing edge noise reduction

2020 ◽  
Vol 19 (6-8) ◽  
pp. 347-364
Author(s):  
Lennart Rossian ◽  
Roland Ewert ◽  
Jan W Delfs
Keyword(s):  
Noise Reduction ◽  
Porous Materials ◽  
Collaborative Research ◽  
Smooth Transition ◽  
Trailing Edge ◽  
High Lift ◽  
Trailing Edge Noise ◽  
Numerical Investigations ◽  
Civil Aircraft ◽  
Numerical Approaches

In the framework of the German Collaborative Research Center CRC 880: Fundamentals of High Lift for Future Civil Aircraft porous materials as a means towards the reduction of airfoil trailing edge noise are investigated. At DLR, both experimental and numerical approaches are pursued to understand the physics behind the noise reduction. The present paper focuses on the numerical investigations, for which the experimental data serves as an evaluation basis. From the analysis of homogeneous materials, first steps are made towards the design of aeroacoustically tailored materials. It is assumed that materials with locally varying permeability may be suitable to achieve maximum noise reduction, as they provide a smooth transition from the solid airfoil to the free flow in the wake. The simulation results support this understanding, however it is revealed that high local gradients in the material properties themselves may act as acoustic sources.

Numerical and Experimental Investigation of Flow Behaviour and Aerodynamic Noise in Axial Flow Fan of Air-Conditioner

2011 ◽  
Author(s):  
Xifeng Zhao ◽  
Jinju Sun ◽  
Zhi Zhang
Keyword(s):  
Hybrid Method ◽  
Performance Test ◽  
Noise Analysis ◽  
Aerodynamic Performance ◽  
Aerodynamic Noise ◽  
Air Conditioner ◽  
Acoustic Analogy ◽  
Fan Noise ◽  
Trailing Edge ◽  
Impeller Blade

To improve aerodynamic performance and reduce noise for a split air conditioner outdoor unit fan, a hybrid method is developed, which combines the Computational Fluid Dynamics (CFD) flow simulation with Computational Aero Acoustics (CAA) noise analysis, where Large Eddy Simulation (LES) model and Ffowcs Williams-Hawkings (FW-H) acoustic analogy model are solved respectively for the unsteady flow characteristics and far field noise solutions. Experimental tests are conducted respectively for fan aerodynamic performance and acoustic behavior, with the aerodynamic performance test rig and semi-anechoic room. Numerical results demonstrates that the main dipole sound sources are located mainly on the blade trailing edge and tip surface, and shroud and casing inner surface, such a distribution is caused by fluctuations in instantaneous pressure associated with rotor-stator interaction. The casing dipole sources contribute largely to the total noise of the fan, and are the main causes for fan noise. It is demonstrated both numerically and experimentally that modifications of impeller blade geometry are effective to reduce the fan noise. Two redesign schemes, the concaved-trailing edge and flanging outer-edge blades, are used, but the latter is more effective in reducing the fan noise as well as shaft power simultaneously. The predicted SPL agrees well with the measured results at the fundamental frequency of the highest intensity, and the hybrid method used in the present study is justified.

Experimental investigation of porous materials for trailing-edge noise reduction

2020 ◽  
Vol 19 (6-8) ◽  
pp. 365-384
Author(s):  
K-S Rossignol ◽  
A Suryadi ◽  
M Herr ◽  
J Schmidt ◽  
J Tychsen
Keyword(s):  
Wind Tunnel ◽  
Noise Reduction ◽  
Porous Materials ◽  
Active Flow Control ◽  
Acoustic Emissions ◽  
Experimental Investigations ◽  
Trailing Edge ◽  
Trailing Edge Noise ◽  
Tunnel Model ◽  
Close Proximity

The introduction of quiet short take-off and landing for civil aircraft operations in close proximity to the population poses important technological challenges. One critical aspect is the realization of extreme lift augmentation at low acoustic emissions. The aircraft concept selected to achieve this goal is a high-lift system equipped with an active flow-control non-slotted flap and a droop nose. For this specific configuration, trailing edge noise becomes a dominant noise source. Porous materials as a passive means for trailing-edge noise reduction are selected and characterized. Results of extensive experimental investigations in the acoustic wind tunnel Braunschweig are presented and discussed to point out the potential and limitations of the selected porous devices. Practical issues related to material manufacturing and integration into the wind tunnel model are addressed. The noise reduction potential of passive porous trailing-edge devices is found to strongly depend on both these aspects. Issues related to the characterization of the porous materials properties are described. Although porous materials are found to be successful at reducing trailing-edge noise emissions, the results indicate that there is still a need for more generic investigations to further clarify the parametric dependencies between noise reduction and material properties.

Adjoint-based Trailing-Edge Noise Minimization using Porous Material

2014 ◽  
Author(s):  
Beckett Yx Zhou ◽  
Nicolas R. Gauger ◽  
Seong Ryong Koh ◽  
Matthias H. Meinke ◽  
Wolfgang Schroeder
Keyword(s):  
Porous Material ◽  
Trailing Edge ◽  
Trailing Edge Noise

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.

Bionics - Natural but Innovative Methods Improve the Aeroacoustic Engineering

2015 ◽  
Vol 806 ◽  
pp. 222-231
Author(s):  
Joanna M. Kopania
Keyword(s):  
Sound Intensity ◽  
Barn Owl ◽  
Aerodynamic Noise ◽  
Tyto Alba ◽  
Flat Plates ◽  
Trailing Edge ◽  
Trailing Edge Noise ◽  
Wing Feather ◽  
Innovative Methods ◽  
Reduction Effect

This paper presents the aeroacoustics result of the trailing edge noise prepared wings two species of owl - Barn owl (Tyto alba), called “good hearing” and Northern hawk-owl (Surnia ulula), called “good seeing”. The acoustic performance comparisons between the Barn owl and Northern hawk-owl show that there are differences between the sound intensity the studied wings. These results prove that the special sound suppression characteristics of wing feather play an important role for their silent flight. Therefore the flat plates with the cutting trailing edge have been studied. At lower speeds, a better noise reduction effect was obtained for the plates with edges as elliptical arcs. On the basis of the above tests it can be concluded that other types of notches on the trailing edge (not just a sawtooth) also reduce the aerodynamic noise of flat plate.

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