467 research outputs found
A lattice Boltzmann study of reactive microflows
The role of geometrical micro-barriers on the conversion efficiency of
reactive flows in narrow three-dimensional channels of millimetric size is
investigated. Using a Lattice-Boltzmann-Lax-Wendroff code, we show that
micro-barriers have an appreciable effect on the effective reaction efficiency
of the device. If extrapolated to macroscopic scales, these effects can result
in a sizeable increase of the overall reaction efficiency.Comment: 5 pages, 7 figure
Chemical efficiency of reactive microflows with heterogeneus catalysis: a lattice Boltzmann study
We investigate the effects of geometrical micro-irregularities on the
conversion efficiency of reactive flows in narrow channels of millimetric size.
Three-dimensional simulations, based upon a Lattice-Boltzmann-Lax-Wendroff
code, indicate that periodic micro-barriers may have an appreciable effect on
the effective reaction efficiency of the device. Once extrapolated to
macroscopic scales, these effects can result in a sizeable increase of the
overall reaction efficiency.Comment: 12 pages, 12 figure
Roughness induced boundary slip in microchannel flows
Surface roughness becomes relevant if typical length scales of the system are
comparable to the scale of the variations as it is the case in microfluidic
setups. Here, an apparent boundary slip is often detected which can have its
origin in the assumption of perfectly smooth boundaries. We investigate the
problem by means of lattice Boltzmann (LB) simulations and introduce an
``effective no-slip plane'' at an intermediate position between peaks and
valleys of the surface. Our simulations show good agreement with analytical
results for sinusoidal boundaries, but can be extended to arbitrary geometries
and experimentally obtained surface data. We find that the detected apparent
slip is independent of the detailed boundary shape, but only given by the
distribution of surface heights. Further, we show that the slip diverges as the
amplitude of the roughness increases.Comment: 4 pages, 6 figure
Random-roughness hydrodynamic boundary conditions
We report results of lattice Boltzmann simulations of a high-speed drainage
of liquid films squeezed between a smooth sphere and a randomly rough plane. A
significant decrease in the hydrodynamic resistance force as compared with that
predicted for two smooth surfaces is observed. However, this force reduction
does not represent slippage. The computed force is exactly the same as that
between equivalent smooth surfaces obeying no-slip boundary conditions, but
located at an intermediate position between peaks and valleys of asperities.
The shift in hydrodynamic thickness is shown to depend on the height and
density of roughness elements. Our results do not support some previous
experimental conclusions on very large and shear-dependent boundary slip for
similar systems.Comment: 4 pages, 4 figure
Quantum Simulator for Transport Phenomena in Fluid Flows
Transport phenomena still stand as one of the most challenging problems in
computational physics. By exploiting the analogies between Dirac and lattice
Boltzmann equations, we develop a quantum simulator based on pseudospin-boson
quantum systems, which is suitable for encoding fluid dynamics transport
phenomena within a lattice kinetic formalism. It is shown that both the
streaming and collision processes of lattice Boltzmann dynamics can be
implemented with controlled quantum operations, using a heralded quantum
protocol to encode non-unitary scattering processes. The proposed simulator is
amenable to realization in controlled quantum platforms, such as ion-trap
quantum computers or circuit quantum electrodynamics processors.Comment: 8 pages, 3 figure
Coupling Lattice Boltzmann and Molecular Dynamics models for dense fluids
We propose a hybrid model, coupling Lattice Boltzmann and Molecular Dynamics
models, for the simulation of dense fluids. Time and length scales are
decoupled by using an iterative Schwarz domain decomposition algorithm. The MD
and LB formulations communicate via the exchange of velocities and velocity
gradients at the interface. We validate the present LB-MD model in simulations
of flows of liquid argon past and through a carbon nanotube. Comparisons with
existing hybrid algorithms and with reference MD solutions demonstrate the
validity of the present approach.Comment: 14 pages, 5 figure
Run-and-tumble particles with hydrodynamics: sedimentation, trapping and upstream swimming
We simulate by lattice Boltzmann the nonequilibrium steady states of
run-and-tumble particles (inspired by a minimal model of bacteria), interacting
by far-field hydrodynamics, subject to confinement. Under gravity, hydrodynamic
interactions barely perturb the steady state found without them, but for
particles in a harmonic trap such a state is quite changed if the run length is
larger than the confinement length: a self-assembled pump is formed. Particles
likewise confined in a narrow channel show a generic upstream flux in
Poiseuille flow: chiral swimming is not required
Efficient simulation of non-crossing fibers and chains in a hydrodynamic solvent
An efficient simulation method is presented for Brownian fiber suspensions,
which includes both uncrossability of the fibers and hydrodynamic interactions
between the fibers mediated by a mesoscopic solvent. To conserve hydrodynamics,
collisions between the fibers are treated such that momentum and energy are
conserved locally. The choice of simulation parameters is rationalised on the
basis of dimensionless numbers expressing the relative strength of different
physical processes. The method is applied to suspensions of semiflexible fibers
with a contour length equal to the persistence length, and a mesh size to
contour length ratio ranging from 0.055 to 0.32. For such fibers the effects of
hydrodynamic interactions are observable, but relatively small. The
non-crossing constraint, on the other hand, is very important and leads to
hindered displacements of the fibers, with an effective tube diameter in
agreement with recent theoretical predictions. The simulation technique opens
the way to study the effect of viscous effects and hydrodynamic interactions in
microrheology experiments where the response of an actively driven probe bead
in a fiber suspension is measured.Comment: 12 pages, 2 tables, 5 figure
Dynamic regimes of hydrodynamically coupled self-propelling particles
We analyze the collective dynamics of self-propelling particles (spps) which
move at small Reynolds numbers including the hydrodynamic coupling to the
suspending solvent through numerical simulations. The velocity distribution
functions show marked deviations from Gaussian behavior at short times, and the
mean-square displacement at long times shows a transition from diffusive to
ballistic motion for appropriate driving mechanism at low concentrations. We
discuss the structures the spps form at long times and how they correlate to
their dynamic behavior.Comment: 7 pages, 4 figure
Mesoscopic model for the fluctuating hydrodynamics of binary and ternary mixtures
A recently introduced particle-based model for fluid dynamics with continuous
velocities is generalized to model immiscible binary mixtures. Excluded volume
interactions between the two components are modeled by stochastic multiparticle
collisions which depend on the local velocities and densities. Momentum and
energy are conserved locally, and entropically driven phase separation occurs
for high collision rates. An explicit expression for the equation of state is
derived, and the concentration dependence of the bulk free energy is shown to
be the same as that of the Widom-Rowlinson model. Analytic results for the
phase diagram are in excellent agreement with simulation data. Results for the
line tension obtained from the analysis of the capillary wave spectrum of a
droplet agree with measurements based on the Laplace's equation. The
introduction of "amphiphilic" dimers makes it possible to model the phase
behavior and dynamics of ternary surfactant mixtures.Comment: 7 pages including 6 figure
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