Circular cylinders with soft porous cover for flow noise reduction

Geyer, Thomas; Sarradj, Ennes

doi:10.1007/s00348-016-2119-7

Cited by 72 publications

(64 citation statements)

References 32 publications

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“…Finally, the data were converted to power spectral densities L p re 20 µPa. The experimental setup is shown in Figure 1(a) and explained in more detail in [5]. In addition to the acoustic measurements from [5], constant temperature anemometry (CTA) measurements were performed in the wake of the cylinders at a single flow speed using a Dantec single-wire P11 probe.…”

Section: Iia Setupmentioning

confidence: 99%

“…In addition to a reduction of noise, such materials also affect the flow around the cylinder and, subsequently, the aerodynamic drag [12][13][14][15][16][17][18][19][20]. In a previous experimental study by the authors [5], the noise reducing effects of a large number of different flow permeable cylinder covers were shown. Thereby, the cylinder models consisted of a non-porous core cylinder on which hollow cylinder disks made of porous material were threaded.…”

Section: Introductionmentioning

confidence: 99%

“…One possible method for the reduction of aeroacoustic noise from cylinders is the use of flow permeable materials, which has been the subject of various studies in the past. This includes both experimental investigations [1][2][3][4][5][6][7] and numerical work [8][9][10][11]. In addition to a reduction of noise, such materials also affect the flow around the cylinder and, subsequently, the aerodynamic drag [12][13][14][15][16][17][18][19][20].…”

Section: Introductionmentioning

confidence: 99%

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Detached Eddy Simulation of the Flow Noise Generation of Cylinders with Porous Cover

Geyer

Sharma

Sarradj

2018

2018 AIAA/CEAS Aeroacoustics Conference

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The use of porous materials is a known method for the reduction of cylinder vortex shedding noise. In a previous experimental wind tunnel study, the noise reducing effect of a modification of circular cylinders with open-porous materials was shown. The cylinder models consisted of a solid core cylinder with porous covers with different material parameters. In order to obtain insight into the flow through the porous materials, the noise generation by such porous-covered cylinders is investigated numerically using Detached-Eddy Simulations. This was done for three different porous material covers as well as for a non-porous reference cylinder at three Reynolds numbers in the critical flow regime. Unlike the observations from the experiments, the numerical results show that fluid enters the porous materials and vortex shedding also takes place at the inner core cylinder, leading to an additional tone in the acoustic far field spectrum. In addition, the porous covers were found to have no effect on the directivity of the aeolian tone and to lead to a notable reduction of the aerodynamic drag.

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Section: Iia Setupmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Detached Eddy Simulation of the Flow Noise Generation of Cylinders with Porous Cover

Geyer

Sharma

Sarradj

2018

2018 AIAA/CEAS Aeroacoustics Conference

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“…The setup and methodology used for the measurement of the flow noise generated by the cylinders is basically identical to that used in the study by Geyer and Sarradj [19] on the noise generated by porous covered cylinders. It consists of an aerodynamically closed test section of approximately 1.5 m length that is mounted to the rectangular nozzle of the open jet wind tunnel, which has a contraction ratio of about 31.2 and an exit area of 0.23 m Ö 0.28 m. The nozzle was specifically built for the purpose of transforming the circular cross section of the wind tunnel to a rectangular cross section at the nozzle exit using the design of Morel [20].…”

Section: Wind Tunnelmentioning

confidence: 99%

“…The flow inside the test section can be described as essentially not turbulent, with turbulence intensities in the order of 0.2 % [19] (measured in front of the nozzle without the test section attached). A very low inflow turbulence was desired for the present measurements, since it is known that even small fluctuations may have a significant effect on the flow [21].…”

Section: Wind Tunnelmentioning

confidence: 99%

Vortex shedding noise of a cylinder with hairy flaps

Kamps

Geyer

Sarradj

et al. 2017

Journal of Sound and Vibration

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This is the accepted version of the paper.This version of the publication may differ from the final published version. Permanent repository link AbstractThis study describes the modification of acoustic noise emitted from cylinders in a stationary subsonic flow for a cylinder equipped with flexible hairy flaps at the aft part as a passive way to manipulate the flow and acoustics. The study was motivated by the results from previous water tunnel measurements, which demonstrated that hairy flaps can modify the shedding cycle behind the cylinder and can reduce the wake deficit. In the present study, wind tunnel experiments were conducted on such a modified cylinder and the results were compared to the reference case of a plain cylinder. The acoustic spectrum was measured using two microphones while simultaneously recording the flap motion. To further examine the flow structures in the downstream vicinity of the cylinder, constant temperature anemometry measurements as well as flow visualizations were also performed. The results show that, above a certain Reynolds number, the hairy flaps lead to a jump in the vortex shedding frequency. This phenomenon is similarly observed in the water flow experiments as a jump in the non-dimensional Strouhal number that is related to the change of the shedding cycle. This jump appears to be coupled to a resonant excitation of the flaps and a considerable increase of the flapping amplitude. The specific Reynolds number at which the jump Email addresses: Laura.Kamps@imfd.tu-freiberg.de (Laura Kamps), Thomas.Geyer@b-tu.de (Thomas F. Geyer) Preprint submitted to Journal of Sound and Vibration October 11, 2016 occurs is higher in the present case, which is attributed to the lower added mass in air as compared with the one in water. The flow visualizations confirmed that such action of the flaps lead to a more slender elongated shape of the time-averaged separation bubble. In addition, the hairy flaps induce a noticeable reduction of the tonal noise as well as broadband noise as long as the flaps do not touch each other.

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Aerodynamic Noise from Circular Cylinder in Low Subcritical Flow Regime Using Large Eddy Simulations

Jacob

Bhattacharyya

2021

Lecture Notes in Mechanical Engineering

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Circular cylinders with soft porous cover for flow noise reduction

Cited by 72 publications

References 32 publications

Detached Eddy Simulation of the Flow Noise Generation of Cylinders with Porous Cover

Detached Eddy Simulation of the Flow Noise Generation of Cylinders with Porous Cover

Vortex shedding noise of a cylinder with hairy flaps

Aerodynamic Noise from Circular Cylinder in Low Subcritical Flow Regime Using Large Eddy Simulations

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