Effect of the liquid–gas interface curvature for a superhydrophobic surface with longitudinal grooves in turbulent flows

Yao, Jie; Teo, C. J.

doi:10.1063/5.0056952

Cited by 14 publications

(3 citation statements)

References 67 publications

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“…The slip length is obtained from = , where is the mean slip velocity, and is the mean velocity gradient of water at the interface. In the study, the average shear stress over the top and bottom walls is calculated by the equation presented in references 37 – 39 : , where G, which is defined by , is the prescribed pressure gradient. The and are the average shear stresses at the top with smooth wall and bottom SHS wall, respectively.…”

Section: Resultsmentioning

confidence: 99%

Numerical investigation of the effect of air layer on drag reduction in channel flow over a superhydrophobic surface

Nguyen,

Lee,

Ryu

et al. 2024

Sci Rep

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This study investigates the effects of an air layer on drag reduction and turbulence dynamics in channel flow over a superhydrophobic surface (SHS). Employing the OpenFOAM platform, direct numerical simulation was conducted to investigate turbulent channel flow with an air layer over an SHS. The simulations, which take into account the interaction between water and air, analyze various parameters such as velocity distribution, drag reduction (DR), Reynolds stress, turbulent kinetic energy (TKE), and coherent structures near the water–air interface. The presence of an air layer significantly alters the velocity distribution, leading to higher velocities at the interface compared to simulations without the air layer. Notably, the thickness of the air layer emerges as an important factor, with larger thicknesses resulting in increased velocities and drag reduction. This study underscores the substantial impact of the air layer on TKE near the superhydrophobic surface, emphasizing its role in understanding and optimizing drag reduction. Furthermore, the nonlinear relationship between slip velocity, Q contours, and coherent structures near the SHS are investigated.

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Section: Resultsmentioning

confidence: 99%

Numerical investigation of the effect of air layer on drag reduction in channel flow over a superhydrophobic surface

Nguyen,

Lee,

Ryu

et al. 2024

Sci Rep

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“…On the other hand, validation and grid size testing are still essential at low Reynolds numbers to find out the appropriate mesh configuration, before the mesh size scaling law can be applied. Similar mesh size scaling law and LES model have been applied in the study of turbulent flow drag reduction by the superhydrophobic surface [51], which has more complex boundary conditions than plane channel flows.…”

Section: Discussionmentioning

confidence: 99%

A Mesh Size Scaling Law with Reynolds Number for Large Eddy Simulation in Channel Flow

Yao¹,

Teo²

2022

AAMM

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In this paper, a scaling law relating the mesh size to the Reynolds number was proposed to ensure consistent results for large eddy simulation (LES) as the Reynolds number was varied. The grid size scaling law was developed by analyzing the lengthscale of the turbulent motion by using DNS data from the literature. The wall-resolving LES was then applied to a plane channel flow to validate the scaling law. The scaling law was tested at different Reynolds numbers (Re τ = 395, 590 and 1000), and showed good results compared to direct numerical simulation (DNS) in terms of mean flow and various turbulent statistics. The velocity spectra analysis shows the evidence of the Kolmogorov -5/3 inertial subrange and verifies that the current LES can resolve the bulk of the turbulent kinetic energy by satisfying the grid scaling law. Meanwhile, the near-wall turbulent flow structures can also be well captured. Reasonably accurate predictions can thus be obtained for flows at even higher Reynolds numbers with significantly lower computational costs compared to DNS by applying the mesh scaling law.

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“…For example, the effects of micro-features on near-wall behaviours were investigated by using LES in the case of a fully slip condition on the SHS (Saadat-Bakhsh, Nouri, & Norouzi, 2017). Others have investigated the effects of SHS curvature at the liquid-gas interface by utilizing LES turbulence methods (Yao & Teo, 2020). However, the utilization of LES methods generally comes with certain complications, including the choice of filtering, closure modelling and near-wall treatment (Goc, Lehmkuhl, Park, Bose, & Moin, 2021).…”

Section: Introductionmentioning

confidence: 99%

Numerical investigation of the drag reduction effect in turbulent channel flow by superhydrophobic grooved surfaces

Safari,

Saidi,

Salavatidezfouli

et al. 2023

Flow

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Superhydrophobic surfaces (SHSs) are considered to be a promising technology for achieving skin-friction drag reduction. Development of more efficient techniques for simulating the turbulent boundary layer on SHSs continues to be a subject of interest. In this study, numerical simulations were carried out to capture near-wall behaviours due to the effect of the SHS on wall-bounded flows. To achieve this, high- to intermediate-fidelity turbulence models including Reynolds-averaged Navier–Stokes, detached eddy simulation and large eddy simulation were utilized. With regard to slip conditions, the well-known Navier slip velocity method was used over the SHS. For validating the numerical solutions, the slip velocity and skin friction over the SHS were compared with the experimental output. Results showed that the velocity profile and Reynolds stresses on the SHS were comparable to the reported results. Then, the developed models were further extended to investigate the drag reduction effect of SHSs with rectangular grooves. The subsequent results showed that the combination of superhydrophobicity and rectangular grooves led to a better performance with a maximum drag reduction of 46.1%. This is due to the surface slip caused by the SHS and the secondary vortex effect created by the grooves. Our results revealed that Reynolds stresses of the slippery grooved surface were higher than those of the case in which a shear-free condition was employed for the grooved surface. More importantly, the numerical results indicate the previous assumption of the shear-free condition is inaccurate for the geometrically simplified grooved SHSs. Therefore, geometry modifications rather than an overly simplified shear-free boundary condition should be applied in computational fluid dynamics simulations for SHSs with grooves or other complex structures.

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Effect of the liquid–gas interface curvature for a superhydrophobic surface with longitudinal grooves in turbulent flows

Cited by 14 publications

References 67 publications

Numerical investigation of the effect of air layer on drag reduction in channel flow over a superhydrophobic surface

Numerical investigation of the effect of air layer on drag reduction in channel flow over a superhydrophobic surface

A Mesh Size Scaling Law with Reynolds Number for Large Eddy Simulation in Channel Flow

Numerical investigation of the drag reduction effect in turbulent channel flow by superhydrophobic grooved surfaces

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