A computational continuum model of poroelastic beds

Lācis, Uǧis; Zampogna, Giuseppe; Bagheri, Shervin

doi:10.1098/rspa.2016.0932

Cited by 20 publications

(28 citation statements)

References 57 publications

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“…The scale separation parameter is again = /H = 0.1. The flow reaches the interior seepage velocity quickly(Lācis & Bagheri 2016;Lācis, Zampogna & Bagheri 2017); therefore, a porous material containing only five repeating structures in depth is sufficient for using Darcy's equation in the interior.…”

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confidence: 99%

Transfer of mass and momentum at rough and porous surfaces

et al. 2019

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The surface texture of materials plays a critical role in wettability, turbulence and transport phenomena. In order to design surfaces for these applications, it is desirable to characterise non-smooth and porous materials by their ability to exchange mass and momentum with flowing fluids. While the underlying physics of the tangential (slip) velocity at a fluid-solid interface is well understood, the importance and treatment of normal (transpiration) velocity and normal stress is unclear. We show that, when slip velocity varies at an interface above the texture, a non-zero transpiration velocity arises from mass conservation. The ability of a given surface texture to accommodate for a normal velocity of this kind is quantified by a transpiration length. We further demonstrate that normal momentum transfer gives rise to a pressure jump. For a porous material, the pressure jump can be characterised by so called resistance coefficients. By solving five Stokes problems, the introduced measures of slip, transpiration and resistance can be determined for any anisotropic non-smooth surface consisting of regularly repeating geometric patterns. The proposed conditions are a subset of effective boundary conditions derived from formal multi-scale expansion. We validate and demonstrate the physical significance of the effective conditions on two canonical problems -a lid-driven cavity and a turbulent channel flow, both with non-smooth bottom surfaces. † Email address for correspondence: ugis@mech.kth.se arXiv:1812.09401v2 [physics.flu-dyn]

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Transfer of mass and momentum at rough and porous surfaces

et al. 2019

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“…In the present work, a multiscale homogenization technique, similar to that used by Jiménez Bolaños & Vernescu (2017), is employed to link the macroscopic and microscopic viewpoints. Since the phenomena under investigation are inhomogeneous in the direction normal to the surface, the standard homogenization technique needs to be adapted through a procedure similar to that followed by and Lācis, Zampogna & Bagheri (2017). The outcome of this approach is a boundary condition which extends the Navier slip concept and contains in itself the formulation and boundary conditions of the microscopic problems to determine the general relationship between the outer flow characteristics (more specifically the various components of the strain rate) and the geometry of the rough layer.…”

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Generalized slip condition over rough surfaces

2018

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A macroscopic boundary condition to be used when a fluid flows over a rough surface is derived. It provides the slip velocity $\boldsymbol{u}_{S}$ on an equivalent (smooth) surface in the form $\boldsymbol{u}_{S}=\unicode[STIX]{x1D716}{\mathcal{L}}\boldsymbol{ : }{\mathcal{E}}$, where the dimensionless parameter $\unicode[STIX]{x1D716}$ is a measure of the roughness amplitude, ${\mathcal{E}}$ denotes the strain-rate tensor associated with the outer flow in the vicinity of the surface and ${\mathcal{L}}$ is a third-order slip tensor arising from the microscopic geometry characterizing the rough surface. This boundary condition represents the tensorial generalization of the classical Navier slip condition. We derive this condition, in the limit of small microscopic Reynolds numbers, using a multi-scale technique that yields a closed system of equations, the solution of which allows the slip tensor to be univocally calculated, once the roughness geometry is specified. We validate this generalized slip condition by considering the flow about a rough sphere, the surface of which is covered with a hexagonal lattice of cylindrical protrusions. Comparisons with direct numerical simulations performed in both laminar and turbulent regimes allow us to assess the validity and limitations of this condition and of the mathematical model underlying the determination of the slip tensor ${\mathcal{L}}$.

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“…distance between the filaments) of the surface, and therefore exploit large-scale motions to increase mixing and entrainment. These surfaces are more conveniently described using effective continuum/homogenisation approaches (Gopinath & Mahadevan 2011;Lācis et al 2017).…”

Section: Discussionmentioning

confidence: 99%

Interaction between hairy surfaces and turbulence for different surface time scales

Sundin

Bagheri

2018

J. Fluid Mech.

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Surfaces with filamentous structures are ubiquitous in nature on many different scales, ranging from forests to micrometer-sized cilia in organs. Hairy surfaces are elastic and porous, and it is not fully understood how they modify turbulence near a wall. The interaction between hairy surfaces and turbulent flows is here investigated numerically in a turbulent channel flow configuration at Re τ ≈ 180. We show that a filamentous bed of a given geometry can modify a turbulent flow very differently depending on the resonance frequency of the surface, which is determined by elasticity and mass of the filaments. Filaments having resonance frequencies lower than the main frequency content of the turbulent wall-shear stress conform to slowly traveling elongated streaky structures, since they are too slow to adapt to fluid forces of higher frequencies. On the other hand, a bed consisting of stiff and low-mass filaments has a high resonance frequency and shows local regions of increased permeability, which results in large entrainment and a vast increase in drag.

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A computational continuum model of poroelastic beds

Cited by 20 publications

References 57 publications

Transfer of mass and momentum at rough and porous surfaces

Transfer of mass and momentum at rough and porous surfaces

Generalized slip condition over rough surfaces

Interaction between hairy surfaces and turbulence for different surface time scales

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