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Elias J. G. Arcondoulis
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5 records found
1
Journal article
(2024)
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Elias J.G. Arcondoulis, Daniele Ragni, Daniele Fiscaletti, Roberto Merino-Martinez, Yu Liu
The attachment of porous media to a blunt trailing edge (TE) can significantly suppress vortex shedding processes and the related tonal noise, yet the near-wall and internal flow fields of porous media are difficult to analyze experimentally and rely on numerical simulations to elucidate the internal flow features. A structured porous trailing edge (SPTE) has been recently designed that follows a methodology of a structured porous coated cylinder. The SPTE acoustic response was compared against randomized porous media with 10 and 30 pores/in. in an anechoic wind tunnel over a range of flow velocities. Acoustic beamforming revealed that the dominant acoustic sources were at the end of the solid plate, even when a porous TE was attached. A region of integration was used to extract acoustic spectra without additional noise sources, revealing that the SPTE possesses superior noise reduction capability. Dipolar directivity patterns were observed at the vortex shedding frequency for each TE, and the coherence between microphones revealed the complex acoustic propagation of the high-frequency content. A wavelet analysis revealed how the SPTE breaks periodic vortex shedding cycles into smaller cycles over a wider frequency range, leading to an overall noise reduction relative to the other TEs.
...
The attachment of porous media to a blunt trailing edge (TE) can significantly suppress vortex shedding processes and the related tonal noise, yet the near-wall and internal flow fields of porous media are difficult to analyze experimentally and rely on numerical simulations to elucidate the internal flow features. A structured porous trailing edge (SPTE) has been recently designed that follows a methodology of a structured porous coated cylinder. The SPTE acoustic response was compared against randomized porous media with 10 and 30 pores/in. in an anechoic wind tunnel over a range of flow velocities. Acoustic beamforming revealed that the dominant acoustic sources were at the end of the solid plate, even when a porous TE was attached. A region of integration was used to extract acoustic spectra without additional noise sources, revealing that the SPTE possesses superior noise reduction capability. Dipolar directivity patterns were observed at the vortex shedding frequency for each TE, and the coherence between microphones revealed the complex acoustic propagation of the high-frequency content. A wavelet analysis revealed how the SPTE breaks periodic vortex shedding cycles into smaller cycles over a wider frequency range, leading to an overall noise reduction relative to the other TEs.
Conference paper
(2024)
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Elias J.G. Arcondoulis, Riccardo Zamponi, İris Alagöz, Francesco Avallone, Chaitanya Paruchuri
The application of a porous coating to a bluff body, such as a cylinder, is an efficient passive flow control method and has applications in wind, aerospace, and civil engineering. Despite its effectiveness in reducing vortex-shedding processes and the associated noise-generating mechanisms, there exists a trade-off in terms of the generation of higher frequency noise. Such acoustic emissions can be irritating to the human ear and thereby diminish some of the benefits of porous media as a form of passive flow and noise control. To date, explanations of the mechanisms responsible for high-frequency noise generation of a porous coated cylinder (PCC) are qualitative, and there is no clear consensus. In this paper, it is hypothesized that the high-frequency noise is caused by local vortex shedding around the structural members of the pores that comprise the porous media on the cylinder windward side. To investigate this claim, a mathematical model is derived based on the premise that a porous cylinder potential flow model accurately captures the total velocity at the outer diameter of a PCC. The acoustic shedding frequencies are assumed to be related to the Strouhal number relationship, and the acoustic intensity is assumed to be consistent with Curle’s theory, where acoustic intensity scales with the sixth power of flow velocity and the characteristic length squared. A lattice-Boltzmann method simulation of a simplified structured PCC, following a previously published design, is used to test the analytical model, yielding excellent agreement with the mathematical model in terms of acoustic intensity and frequency range.
...
The application of a porous coating to a bluff body, such as a cylinder, is an efficient passive flow control method and has applications in wind, aerospace, and civil engineering. Despite its effectiveness in reducing vortex-shedding processes and the associated noise-generating mechanisms, there exists a trade-off in terms of the generation of higher frequency noise. Such acoustic emissions can be irritating to the human ear and thereby diminish some of the benefits of porous media as a form of passive flow and noise control. To date, explanations of the mechanisms responsible for high-frequency noise generation of a porous coated cylinder (PCC) are qualitative, and there is no clear consensus. In this paper, it is hypothesized that the high-frequency noise is caused by local vortex shedding around the structural members of the pores that comprise the porous media on the cylinder windward side. To investigate this claim, a mathematical model is derived based on the premise that a porous cylinder potential flow model accurately captures the total velocity at the outer diameter of a PCC. The acoustic shedding frequencies are assumed to be related to the Strouhal number relationship, and the acoustic intensity is assumed to be consistent with Curle’s theory, where acoustic intensity scales with the sixth power of flow velocity and the characteristic length squared. A lattice-Boltzmann method simulation of a simplified structured PCC, following a previously published design, is used to test the analytical model, yielding excellent agreement with the mathematical model in terms of acoustic intensity and frequency range.
Conference paper
(2022)
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Elias J. G. Arcondoulis, Yu Liu, Yannian Yang, D. Ragni, A. Rubio Carpio, F. Avallone
The application of a porous coating to a cylinder can significantly reduce the vortex shedding tone when placed in a uniform flow. The mechanism of how this porous media attenuates vortex shedding has been studied more in recent years yet it is still not fully understood. Typical porous materials within a certain range of porosity and airflow resistivity, such as metal foam and porous polyurethane, have been studied extensively; however, the fundamental flow mechanisms responsible for vortex shedding attenuation are very difficult to determine. For example, it is nearly impossible to visualize the internal flow field of porous media with a randomized open-cell internal structure. A Structured Porous Coated Cylinder (SPCC) was designed in recent years to alleviate this internal flow field problem, as the SPCC has clear line of sight along the span and radial direction. SPCC variations have been previously studied and shown to reduce the vortex shedding tone of a bare cylinder in a very similar manner as a randomized porous coated cylinder. In this paper, we present a Tomographic Particle Image Velocimetry study of an SPCC tested in a water tunnel, revealing the previously unseen internal and near-wall flow fields of an SPCC. The flow is visualized in the porous layers, revealing complex interaction between the freestream flow field and the porous structure. Using cross-correlation methods within the flow field, we reveal the entrainment of the flow within the porous layers. Furthermore, implementation of Proper Orthogonal Decomposition shows that vortex shedding occurs within the porous layers.
...
The application of a porous coating to a cylinder can significantly reduce the vortex shedding tone when placed in a uniform flow. The mechanism of how this porous media attenuates vortex shedding has been studied more in recent years yet it is still not fully understood. Typical porous materials within a certain range of porosity and airflow resistivity, such as metal foam and porous polyurethane, have been studied extensively; however, the fundamental flow mechanisms responsible for vortex shedding attenuation are very difficult to determine. For example, it is nearly impossible to visualize the internal flow field of porous media with a randomized open-cell internal structure. A Structured Porous Coated Cylinder (SPCC) was designed in recent years to alleviate this internal flow field problem, as the SPCC has clear line of sight along the span and radial direction. SPCC variations have been previously studied and shown to reduce the vortex shedding tone of a bare cylinder in a very similar manner as a randomized porous coated cylinder. In this paper, we present a Tomographic Particle Image Velocimetry study of an SPCC tested in a water tunnel, revealing the previously unseen internal and near-wall flow fields of an SPCC. The flow is visualized in the porous layers, revealing complex interaction between the freestream flow field and the porous structure. Using cross-correlation methods within the flow field, we reveal the entrainment of the flow within the porous layers. Furthermore, implementation of Proper Orthogonal Decomposition shows that vortex shedding occurs within the porous layers.
Conference paper
(2021)
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Elias J. G. Arcondoulis, Yu Liu, Yannian Yang, D. Ragni, A. Rubio Carpio, F. Avallone
View Video Presentation: https://doi-org.tudelft.idm.oclc.org/10.2514/6.2021-2226.vid
The mechanisms responsible for vortex shedding reduction, due to the application of a porous coating to a smooth cylinder placed in uniform flow, are still uncertain despite several numerical and experimental studies. To help understand these mechanisms, a transparent Structured Porous Coated Cylinder (SPCC) was manufactured to investigate the internal and near-wall flow fields. The SPCC mimics the more commonly used porous materials such as metal foam and polyurethane, that possess randomized structures preventing a clear line-of-sight along the span and circumference of the porous layers. Tomographic Particle Image Velocimetry was used in a water-tunnel facility to investigate three small regions of an SPCC, on the windward, mid-region and leeward sides. In this paper, previously unseen experimentally obtained internal flow fields of a porous coated cylinder are presented. The following summarize the key observations (1) stagnation from freestream flow to the inner cylinder diameter in the windward region, (2) boundary layer profiles within the porous layer in the circumferential mid-region and (3) bleeding from the porous layer into the wake in the leeward region. These results provide key experimental findings for comparison and validation of numerical simulations of bulk porous media, such as the Darcy-Forscheimer method used in conjunction with the Ffowcs Williams-Hawkings acoustic analogy. ...
The mechanisms responsible for vortex shedding reduction, due to the application of a porous coating to a smooth cylinder placed in uniform flow, are still uncertain despite several numerical and experimental studies. To help understand these mechanisms, a transparent Structured Porous Coated Cylinder (SPCC) was manufactured to investigate the internal and near-wall flow fields. The SPCC mimics the more commonly used porous materials such as metal foam and polyurethane, that possess randomized structures preventing a clear line-of-sight along the span and circumference of the porous layers. Tomographic Particle Image Velocimetry was used in a water-tunnel facility to investigate three small regions of an SPCC, on the windward, mid-region and leeward sides. In this paper, previously unseen experimentally obtained internal flow fields of a porous coated cylinder are presented. The following summarize the key observations (1) stagnation from freestream flow to the inner cylinder diameter in the windward region, (2) boundary layer profiles within the porous layer in the circumferential mid-region and (3) bleeding from the porous layer into the wake in the leeward region. These results provide key experimental findings for comparison and validation of numerical simulations of bulk porous media, such as the Darcy-Forscheimer method used in conjunction with the Ffowcs Williams-Hawkings acoustic analogy. ...
View Video Presentation: https://doi-org.tudelft.idm.oclc.org/10.2514/6.2021-2226.vid
The mechanisms responsible for vortex shedding reduction, due to the application of a porous coating to a smooth cylinder placed in uniform flow, are still uncertain despite several numerical and experimental studies. To help understand these mechanisms, a transparent Structured Porous Coated Cylinder (SPCC) was manufactured to investigate the internal and near-wall flow fields. The SPCC mimics the more commonly used porous materials such as metal foam and polyurethane, that possess randomized structures preventing a clear line-of-sight along the span and circumference of the porous layers. Tomographic Particle Image Velocimetry was used in a water-tunnel facility to investigate three small regions of an SPCC, on the windward, mid-region and leeward sides. In this paper, previously unseen experimentally obtained internal flow fields of a porous coated cylinder are presented. The following summarize the key observations (1) stagnation from freestream flow to the inner cylinder diameter in the windward region, (2) boundary layer profiles within the porous layer in the circumferential mid-region and (3) bleeding from the porous layer into the wake in the leeward region. These results provide key experimental findings for comparison and validation of numerical simulations of bulk porous media, such as the Darcy-Forscheimer method used in conjunction with the Ffowcs Williams-Hawkings acoustic analogy.
The mechanisms responsible for vortex shedding reduction, due to the application of a porous coating to a smooth cylinder placed in uniform flow, are still uncertain despite several numerical and experimental studies. To help understand these mechanisms, a transparent Structured Porous Coated Cylinder (SPCC) was manufactured to investigate the internal and near-wall flow fields. The SPCC mimics the more commonly used porous materials such as metal foam and polyurethane, that possess randomized structures preventing a clear line-of-sight along the span and circumference of the porous layers. Tomographic Particle Image Velocimetry was used in a water-tunnel facility to investigate three small regions of an SPCC, on the windward, mid-region and leeward sides. In this paper, previously unseen experimentally obtained internal flow fields of a porous coated cylinder are presented. The following summarize the key observations (1) stagnation from freestream flow to the inner cylinder diameter in the windward region, (2) boundary layer profiles within the porous layer in the circumferential mid-region and (3) bleeding from the porous layer into the wake in the leeward region. These results provide key experimental findings for comparison and validation of numerical simulations of bulk porous media, such as the Darcy-Forscheimer method used in conjunction with the Ffowcs Williams-Hawkings acoustic analogy.
Conference paper
(2019)
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Elias J. G. Arcondoulis, Daniele Ragni, Alejandro Rubio Carpio, Francesco Avallone, Yu Liu, Yannian Yang, Zhiyong Li
Porous coated cylinders have been shown to reduce the vortex shedding tone and broadband noise of a bare cylinder placed in uniform flow within specific Reynolds number regimes. The processes by which the vortex shedding and thus tone suppression take place are still uncertain despite numerous numerical and experimental studies. It is understood that adding a porous medium to a bare cylinder will have an influence on the Reynolds number of cylinder, yet the increase of outer diameter alone and the influences of surface roughness are insufficient to explain the changes in the shedding tone magnitude and frequency that are observed by many. Investigating the internal flow field of a porous coated cylinder could lead to a deeper understanding of the flow processes that result in the tonal noise reduction. This has not been achieved to date, as commonly used materials such as metal foam and polyurethane possess randomized porous structures, which make investigating the internal flow field nearly impossible without affecting the structure itself. This paper presents a preliminary analysis of the internal and external flow fields of two structured porous coated cylinders. The cylinders were manufactured using solid transparent materials that possess direct lines of sight through the pores in the axial and spanwise directions. Such structured porous coated cylinders have been previously successful in reducing the typical vortex shedding tone. Tomographic and 2-D planar Particle Image Velocimetry (PIV) were used in a water-tunnel facility to visualize the internal and external flow fields. To date only the 2-D planar PIV results have been post-processed that reveal differences in the wake for the two different cylinder types such as recirculation of flow around the pores. Vorticity flow structures are observed to vary along the cylinder span in the same pattern as the porous structure and streamlines at the windward cylinder side reveal the entry of flow into the porous medium.
...
Porous coated cylinders have been shown to reduce the vortex shedding tone and broadband noise of a bare cylinder placed in uniform flow within specific Reynolds number regimes. The processes by which the vortex shedding and thus tone suppression take place are still uncertain despite numerous numerical and experimental studies. It is understood that adding a porous medium to a bare cylinder will have an influence on the Reynolds number of cylinder, yet the increase of outer diameter alone and the influences of surface roughness are insufficient to explain the changes in the shedding tone magnitude and frequency that are observed by many. Investigating the internal flow field of a porous coated cylinder could lead to a deeper understanding of the flow processes that result in the tonal noise reduction. This has not been achieved to date, as commonly used materials such as metal foam and polyurethane possess randomized porous structures, which make investigating the internal flow field nearly impossible without affecting the structure itself. This paper presents a preliminary analysis of the internal and external flow fields of two structured porous coated cylinders. The cylinders were manufactured using solid transparent materials that possess direct lines of sight through the pores in the axial and spanwise directions. Such structured porous coated cylinders have been previously successful in reducing the typical vortex shedding tone. Tomographic and 2-D planar Particle Image Velocimetry (PIV) were used in a water-tunnel facility to visualize the internal and external flow fields. To date only the 2-D planar PIV results have been post-processed that reveal differences in the wake for the two different cylinder types such as recirculation of flow around the pores. Vorticity flow structures are observed to vary along the cylinder span in the same pattern as the porous structure and streamlines at the windward cylinder side reveal the entry of flow into the porous medium.