21 research outputs found
Flow past superhydrophobic surfaces with cosine variation in local slip length
Anisotropic super-hydrophobic surfaces have the potential to greatly reduce
drag and enhance mixing phenomena in microfluidic devices. Recent work has
focused mostly on cases of super-hydrophobic stripes. Here, we analyze a
relevant situation of cosine variation of the local slip length. We derive
approximate formulae for maximal (longitudinal) and minimal (transverse)
directional effective slip lengths that are in good agreement with the exact
numerical solution and lattice-Bolzmann simulations for any surface slip
fraction. The cosine texture can provide a very large effective (forward) slip,
but it was found to be less efficient in generating a transverse flow as
compared to super-hydrophobic stripes.Comment: 8 pages, 6 figure
Tensorial slip of super-hydrophobic channels
We describe a generalization of the tensorial slip boundary condition,
originally justified for a thick (compared to texture period) channel, to any
channel thickness. The eigenvalues of the effective slip length tensor,
however, in general case become dependent on the gap and cannot be viewed as a
local property of the surface, being a global characteristic of the channel. To
illustrate the use of the tensor formalism we develop a semi-analytical theory
of an effective slip in a parallel-plate channel with one super-hydrophobic
striped and one hydrophilic surface. Our approach is valid for any local slip
at the gas sectors and an arbitrary distance between the plates, ranging from a
thick to a thin channel. We then present results of lattice Boltzmann
simulations to validate the analysis. Our results may be useful for extracting
effective slip tensors from global measurements, such as the permeability of a
channel, in experiments or simulations.Comment: 12 pages, 7 figure
Mesoscopic simulation of diffusive contaminant spreading in gas flows at low pressure
Many modern production and measurement facilities incorporate multiphase
systems at low pressures. In this region of flows at small, non-zero Knudsen-
and low Mach numbers the classical mesoscopic Monte Carlo methods become
increasingly numerically costly. To increase the numerical efficiency of
simulations hybrid models are promising. In this contribution, we propose a
novel efficient simulation approach for the simulation of two phase flows with
a large concentration imbalance in a low pressure environment in the low
intermediate Knudsen regime. Our hybrid model comprises a lattice-Boltzmann
method corrected for the lower intermediate Kn regime proposed by Zhang et al.
for the simulation of an ambient flow field. A coupled event-driven
Monte-Carlo-style Boltzmann solver is employed to describe particles of a
second species of low concentration. In order to evaluate the model, standard
diffusivity and diffusion advection systems are considered.Comment: 9 pages, 8 figure
Lattice-Boltzmann simulations of the drag force on a sphere approaching a superhydrophobic striped plane
By means of lattice-Boltzmann simulations the drag force on a sphere of
radius R approaching a superhydrophobic striped wall has been investigated as a
function of arbitrary separation h. Superhydrophobic (perfect-slip vs. no-slip)
stripes are characterized by a texture period L and a fraction of the gas area
. For very large values of h/R we recover the macroscopic formulae for a
sphere moving towards a hydrophilic no-slip plane. For h/R=O(1) and smaller the
drag force is smaller than predicted by classical theories for hydrophilic
no-slip surfaces, but larger than expected for a sphere interacting with a
uniform perfectly slipping wall. At a thinner gap, the force reduction
compared to a classical result becomes more pronounced, and is maximized by
increasing . In the limit of very small separations our simulation data
are in quantitative agreement with an asymptotic equation, which relates a
correction to a force for superhydrophobic slip to texture parameters. In
addition, we examine the flow and pressure field and observe their oscillatory
character in the transverse direction in the vicinity of the wall, which
reflects the influence of the heterogeneity and anisotropy of the striped
texture. Finally, we investigate the lateral force on the sphere, which is
detectable in case of very small separations and is maximized by stripes with
.Comment: 9 pages, 7 figure
LB3D: A Parallel Implementation of the Lattice-Boltzmann Method for Simulation of Interacting Amphiphilic Fluids
We introduce the lattice-Boltzmann code LB3D, version 7.1. Building on a parallel program and supporting tools which have enabled research utilising high performance computing resources for nearly two decades, LB3D version 7 provides a subset of the research code functionality as an open source project. Here, we describe the theoretical basis of the algorithm as well as computational aspects of the implementation. The software package is validated against simulations of meso-phases resulting from self-assembly in ternary fluid mixtures comprising immiscible and amphiphilic components such as water–oil–surfactant systems. The impact of the surfactant species on the dynamics of spinodal decomposition are tested and quantitative measurement of the permeability of a body centred cubic (BCC) model porous medium for a simple binary mixture is described. Single-core performance and scaling behaviour of the code are reported for simulations on current supercomputer architectures
Simulations of slip flow on nanobubble-laden surfaces
On microstructured hydrophobic surfaces, geometrical patterns may lead to the
appearance of a superhydrophobic state, where gas bubbles at the surface can
have a strong impact on the fluid flow along such surfaces. In particular, they
can strongly influence a detected slip at the surface. We present two-phase
lattice Boltzmann simulations of a flow over structured surfaces with attached
gas bubbles and demonstrate how the detected slip depends on the pattern
geometry, the bulk pressure, or the shear rate. Since a large slip leads to
reduced friction, our results allow to assist in the optimization of
microchannel flows for large throughput.Comment: 22 pages, 12 figure
Lattice-Boltzmann simulations of the drag force on a sphere approaching a superhydrophobic striped plane
LB3D: A parallel implementation of the Lattice-Boltzmann method for mesoscale simulation of interacting amphiphilic fluids
We introduce the lattice-Boltzmann code LB3D, version 7.1. Building on a parallel program and supporting tools which have enabled research utilising high performance computing resources for more than 16 years, LB3D version 7 provides a subset of the research code functionality as an open source project. Here, we describe the theoretical basis of the algorithm as well as computational aspects of the implementation. The software package is validated against simulations of meso-phases resulting from self-assembly in ternary fluid mixtures comprising immiscible and amphiphilic components such as water-oil-surfactant systems. The impact of the surfactant species on the dynamics of spinodal decomposition are tested and quantitative measurement of the permeability of a body centred cubic (BCC) model porous medium for a simple binary mixure is reported. Single-core performance and scaling behaviour of the code are reported for simulations on current supercomputer architectures
LB3D: A parallel implementation of the Lattice-Boltzmann method for mesoscale simulation of interacting amphiphilic fluids
We introduce the lattice-Boltzmann code LB3D, version 7.1. Building on a parallel program and supporting tools which have enabled research utilising high performance computing resources for more than 16 years, LB3D version 7 provides a subset of the research code functionality as an open source project. Here, we describe the theoretical basis of the algorithm as well as computational aspects of the implementation. The software package is validated against simulations of meso-phases resulting from self-assembly in ternary fluid mixtures comprising immiscible and amphiphilic components such as water-oil-surfactant systems. The impact of the surfactant species on the dynamics of spinodal decomposition are tested and quantitative measurement of the permeability of a body centred cubic (BCC) model porous medium for a simple binary mixure is reported. Single-core performance and scaling behaviour of the code are reported for simulations on current supercomputer architectures