On the influence of porous coating thickness and permeability on passive flow and noise control of cylinders

Sharma, Sparsh; Geyer, Thomas; Arcondoulis, Elias

doi:10.1016/j.jsv.2023.117563

Cited by 11 publications

(5 citation statements)

References 64 publications

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“…A comparison of streamwise flow-component time-averaged wake profiles published by Sharma et al. (2023) (PCC) and Arcondoulis et al. (2021 b ) (SPCC) at a similar Reynolds number and porosity recorded at a downstream station of shows excellent agreement within 2 %.…”

Section: Introductionmentioning

confidence: 60%

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Internal shear layer and vortex shedding development of a structured porous coated cylinder using tomographic particle image velocimetry

et al. 2023

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Vortex shedding in the wake of a cylinder in uniform flow can be suppressed via the application of a porous coating; however, the suppression mechanism is not fully understood. The internal flow field of a porous coated cylinder (PCC) can provide a deeper understanding of how the flow within the porous medium affects the wake development. A structured PCC (SPCC) was three-dimensionally printed using a transparent material and tested in water tunnel facilities using flow visualisation and tomographic particle image velocimetry at outer-diameter Reynolds numbers of $Re = 7 \times 10^{3}$ and $7.3 \times 10^{4}$ , respectively. The internal and near-wall flow fields are analysed at the windward and mid-circumference regions. Flow stagnation is observed in the porous layer on the windward side and its boundary is shown to fluctuate with time in the outermost porous layer. This stagnation region generates a quasi-aerodynamic body that influences boundary layer development on the SPCC inner diameter, that separates into a shear layer within the porous medium. For the first time via experiment, spectral content within the separated shear layer reveals vortex shedding processes emanating through single pores at the outer diameter, providing strong evidence that SPCC vortex shedding originates from the inner diameter. Velocity fluctuations linked to this vortex shedding propagate through the porous layers into the external flow field at a velocity less than that of the free stream. The Strouhal number linked to this velocity accurately predicts the SPCC vortex shedding frequency.

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Section: Introductionmentioning

confidence: 60%

“…2020 b ; Zhang et al. 2020) and airflow resistivity (Geyer 2020, 2022 a ; Sharma, Geyer & Arcondoulis 2023). The typical PPI range of common randomised porous media (such as metal foam or porous polyurethane) is from 5 to 30 PPI (Sueki et al.…”

Section: Introductionmentioning

confidence: 99%

Internal shear layer and vortex shedding development of a structured porous coated cylinder using tomographic particle image velocimetry

et al. 2023

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“…Until now, studies of solid cylinders with porous outer layers have principally focused on applications in flow control and vibration damping (Bhattacharyya and Singh 2011), aerodynamic noise reduction (Sueki et al 2010, Liu et al 2014, Geyer 2020, Sharma et al 2023 or heat transfer (Sobera et al 2003). The few investigations of the drag on solid cylinders with porous outer layers have been mostly numerical in nature (e.g.…”

Section: Effect Of Porous Outer Layersmentioning

confidence: 99%

Drag on circular cylinders with porous outer layers in turbulent cross-flow

Cohen,

Blais,

Mydlarski

et al. 2024

Fluid Dyn. Res.

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The effects of free-stream turbulence intensity and porosity on the drag on cylinders with porous outer layers in cross-flow was investigated experimentally. This work is motivated by the need to better model spotting -- a forest fire propagation mechanism in which burning branches and other debris (termed firebrands) are transported away from the main fire by the prevailing wind and ignite new fires. Multiple levels of background turbulence were studied by using no grid, passive grids, and an active grid to generate turbulence intensities of 0.4%, 1.7%, 2.7% and 12.4%. The porous char-layer on the outer surface of firebrands was mimicked by wrapping wire meshes (of 10, 20 and 40 pores-per-inch or PPI) around the cylinders, each to three different fractions (1/16, 1/8 and 1/4) of the cylinder's outer diameter. The drag on one smooth cylinder and nine cylinders with porous outer layers was measured for Reynolds numbers in the range 7000 to 17000, at the aforementioned four turbulence intensities. The results showed that i) the free-stream turbulence intensity and PPI of the wire meshes affect the Reynolds number dependence of the drag coefficient; ii) the drag coefficient increases with free-stream turbulence intensity when it is relatively low (0.4%-2.7%), then decreases at high intensities (12.4%), and this decrease is more pronounced as the PPI increases; iii) the drag coefficient increases with the thickness of the porous layer, and asymptotes to an effectively constant value after a critical thickness of about 1/8 of the cylinder's diameter; and iv) the drag coefficient exhibits a non-monotonic dependence on the PPI of the wire mesh. These results demonstrate the importance of free-stream turbulence intensity and the (porosity and depth of the) porous outer layers of cylinders when modeling the drag on firebrands, or in any other application in which cylinders have porous surfaces.

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“…p ref has a reference value of 2 × 10 −5 N/m 2 . The implementation of Curle's equation is validated in [25,26].…”

Section: Noise Generationmentioning

confidence: 99%

Efficient Prediction of Turbulent Inflow and Leading-Edge Interaction Noise Using a Vortex Particle Method with Look-up Table Approach

Sharma,

Herr

2024

J. Phys.: Conf. Ser.

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This paper presents a new, efficient approach for predicting turbulent inflow, also known as leading-edge interaction noise. The method combines a low-fidelity Vortex Particle Method (VPM) with a look-up table approach. Its goal is to reconstruct realistic inflow turbulence and airfoil contours using stochastic control variables within a limited vortex window. To model far-field sound emission, Curle’s equation and a vortex sound database are employed. To increase confidence in the methodology, an analysis of inflow turbulence parameters and source characteristics was performed using systematic Large Eddy Simulations (LES). A generic NACA 0012 airfoil test case with different inflow turbulence grids was used for direct comparisons with semi-theoretical and semi-empirical predictions from the literature. The comparison is restricted to Amiet/Gershfeld predictions as the current model is only capable of dealing with homogeneous and isotropic turbulence. However, their usefulness is limited to narrower parameter ranges when compared to the more generally applicable new method. A satisfactory agreement of the results demonstrates the versatility of the proposed method.

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On the influence of porous coating thickness and permeability on passive flow and noise control of cylinders

Cited by 11 publications

References 64 publications

Internal shear layer and vortex shedding development of a structured porous coated cylinder using tomographic particle image velocimetry

Internal shear layer and vortex shedding development of a structured porous coated cylinder using tomographic particle image velocimetry

Drag on circular cylinders with porous outer layers in turbulent cross-flow

Efficient Prediction of Turbulent Inflow and Leading-Edge Interaction Noise Using a Vortex Particle Method with Look-up Table Approach

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