Numerical investigation of porous materials for trailing edge noise reduction

Rossian, Lennart; Ewert, Roland; Delfs, Jan

doi:10.1177/1475472x20954410

Cited by 11 publications

(6 citation statements)

References 35 publications

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“…This results in an irregular structure with open pores once the sodium-chloride particles are washed out (Figure 2). The material was used because it showed promising aeroacoustic behavior and good formability by rolling [1,17,18,21,31,32]. The open porosity of up to 60% pore volume fraction allows compaction in a wide range without completely preventing flow through the material (closed porosity).…”

Section: Methodsmentioning

confidence: 99%

“…As part of the finalized CRC880 research project, various materials were investigated to be used as so-called low-noise trailing edges [1,[16][17][18]. The material is not used to dampen sound waves that have already been generated.…”

Section: Introductionmentioning

confidence: 99%

“…However, by attaching porous materials, a sudden transition is created at the point of attachment, which results in a sound source. Aeroacoustic simulations have shown that a porosity gradient along the overflow direction can significantly improve aeroacoustic behavior [18][19][20]. The sound source at the trailing edge is mitigated, and a gradient transition from solid airfoil to porous insert can prevent the emergence of a second source.…”

Section: Introductionmentioning

confidence: 99%

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Investigation of the Porosity Gradient in Thickness Direction Formed by Cold Rolling in Porous Aluminum

Tychsen

Rösler

2023

Metals

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To adapt porous material for its application as low noise trailing edge, a special rolling process, using a time-varied rolling gap, was used in previous research to produce a porosity gradient in the direction of rolling. Investigations suggest that a gradient in porosity may also be produced in the thickness direction of the material, i.e., in the rolling gap direction, without using a specialized rolling mill. Such a gradient may help to further increase acoustic efficiency of porous materials. The aim of this study was to analyze the dependency of such a gradient on the rolling parameters, and to clarify which stress components are significantly responsible for an increased near-surface compaction. Experiments using different relative compressed lengths were performed to analyze shear-dominated and friction-dominated rolling. The material was characterized using compression tests, computed tomography and flow resistance measurements. It is shown that the compressed length is an important parameter for adjusting a porosity gradient. Rolling with small values of compressed length during all rolling passes leads to increased compaction of near-surface regions, compared to interior ones. The difference in porosity achieved was up to 15%. Furthermore, the results suggested that a gradient in hydrostatic stress is responsible for the porosity gradient. Validation of the results by FE simulation is forthcoming, but not part of this publication.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Investigation of the Porosity Gradient in Thickness Direction Formed by Cold Rolling in Porous Aluminum

Tychsen

Rösler

2023

Metals

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“…While numerical methods like stochastic, synthetic turbulence [6][7][8], large eddy simulation [9][10][11], or direct numerical simulation [12][13][14][15] techniques have also been applied to study trailing edge noise, these models are not attractive for the integration in fast design tools. However, the detailed insights into the flow structures can help to advance analytical methods.…”

Section: Introductionmentioning

confidence: 99%

On the Modeling of Wall Surface Pressure Spectra for Trailing Edge Noise Prediction

Kissner

Guérin

Thisse

et al. 2022

28th AIAA/CEAS Aeroacoustics 2022 Conference

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Broadband noise is a significant source for open rotors and Ultra High Bypass Ratio fans. The analytical description of the leading edge noise component is typically linked to the upwash velocity autospectrum of the impinging turbulence, and the modeling of the trailing edge component due to the interaction of the boundary layer turbulence with the trailing edge relies on the surface pressure autospectrum near the trailing edge. But while there is some consensus on describing transverse velocity frequency spectra for leading edge noise, there are a plethora of different models of varying complexity to describe wall surface pressure autospectra. Choosing an appropriate model to apply in the framework of fast and robust acoustic prediction tools is therefore no easy task. This paper aims to apply different models for predicting the surface pressure spectrum near the trailing edge of an airfoil. Experimental data for two airfoils at realistic flight Mach and Reynolds numbers were studied and different RANSinformed empirical models as well as the Stalnov TNO model were investigated regarding their ability to capture experimental trends.

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“…One of the most widely studied noise reduction methods is the sawtooth serrations. 7,[12][13][14][15][16][17][18] Other studies investigated the possibilities of using trailing edge brushes, 19,20 porous materials, [21][22][23][24][25][26] morphing, 27 and flow control. [28][29][30] Recently, a new category of TE noise reduction strategies have been introduced, the trailing-edge finlets, where a series of vertical streamwise blades are used in the close vicinity of the TE to separate turbulence from the surface and to break up the turbulent structures before passing over the TE.…”

Section: Introductionmentioning

confidence: 99%

Flow Field Analysis Around Pressure Shielding Structures

Szőke

Hari

Devenport

et al. 2021

Aiaa Aviation 2021 Forum

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The flow field around a series of streamwise rods, referred to as canopies, is investigated using two-dimensional two-component time-resolved particle image velocimetry (PIV) and large eddy simulations (LES) to characterize the changes in the flow field responsible for reducing the low and high-frequency surface pressure fluctuations previously observed. It was found that an axisymmetric turbulent boundary layer (ATBL) develops over the rods, whose thickness grows at a greater rate above the rods than below. This boundary layer reaches the wall below the rods at a point where previously a saturation was found in the low-frequency noise attenuation, revealing that the ATBL is responsible for the lowfrequency noise attenuation. The flow is displaced by the presence of the rods, particularly above them, which offset was primarily caused by the blockage of the ATBL. The flow below the rods exhibits the properties of a turbulent boundary layer as its profile still conforms to the logarithmic layer, but the friction velocity was found to drop. This viscous effect was found to be responsible for the high-frequency noise attenuation reported previously.

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Numerical investigation of porous materials for trailing edge noise reduction

Cited by 11 publications

References 35 publications

Investigation of the Porosity Gradient in Thickness Direction Formed by Cold Rolling in Porous Aluminum

Investigation of the Porosity Gradient in Thickness Direction Formed by Cold Rolling in Porous Aluminum

On the Modeling of Wall Surface Pressure Spectra for Trailing Edge Noise Prediction

Flow Field Analysis Around Pressure Shielding Structures

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