320 research outputs found
Rheological properties of sheared vesicle and cell suspensions
Numerical simulations of vesicle suspensions are performed in two dimensions
to study their dynamical and rheological properties. An hybrid method is
adopted, which combines a mesoscopic approach for the solvent with a
curvature-elasticity model for the membrane. Shear flow is induced by two
counter-sliding parallel walls, which generate a linear flow profile. The flow
behavior is studied for various vesicle concentrations and viscosity ratios
between the internal and the external fluid. Both the intrinsic viscosity and
the thickness of depletion layers near the walls are found to increase with
increasing viscosity ratio.Comment: To be published in the DynaCaps 2014 Conference Proceedings (Procedia
IUTAM
Dynamics and Rheology of Vesicle Suspensions in Wall-Bounded Shear Flow
The dynamics and rheology of suspensions of fluid vesicles or red blood cells
is investigated by a combination of molecular dynamics and mesoscale
hydrodynamics simulations in two dimensions. The vesicle suspension is confined
between two no-slip walls, which are driven externally to generate a shear flow
with shear rate . The flow behavior is studied as a function of
, the volume fraction of vesicles, and the viscosity contrast
between inside and outside fluids. Results are obtained for the encounter and
interactions of two vesicles, the intrinsic viscosity of the suspension, and
the cell-free layer near the walls.Comment: In press in EP
Phase-ordering dynamics of binary mixtures with field-dependent mobility in shear flow
The effect of shear flow on the phase-ordering dynamics of a binary mixture
with field-dependent mobility is investigated. The problem is addressed in the
context of the time-dependent Ginzburg-Landau equation with an external
velocity term, studied in self-consistent approximation. Assuming a scaling
ansatz for the structure factor, the asymptotic behavior of the observables in
the scaling regime can be analytically calculated. All the observables show
log-time periodic oscillations which we interpret as due to a cyclical
mechanism of stretching and break-up of domains. These oscillations are dumped
as consequence of the vanishing of the mobility in the bulk phase.Comment: 9 pages, 4 figures, EPJ styl
A lattice Boltzmann study of phase separation in liquid-vapor systems with gravity
Phase separation of a two-dimensional van der Waals fluid subject to a
gravitational force is studied by numerical simulations based on lattice
Boltzmann methods (LBM) implemented with a finite difference scheme. A growth
exponent is measured in the direction of the external force.Comment: To appear in Communications in Computational Physics (CiCP
Hybrid lattice Boltzmann model for binary fluid mixtures
A hybrid lattice Boltzmann method (LBM) for binary mixtures based on the
free-energy approach is proposed. Non-ideal terms of the pressure tensor are
included as a body force in the LBM kinetic equations, used to simulate the
continuity and Navier-Stokes equations. The convection-diffusion equation is
studied by finite difference methods. Differential operators are discretized in
order to reduce the magnitude of spurious velocities. The algorithm has been
shown to be stable and reproducing the correct equilibrium behavior in simple
test configurations and to be Galilean invariant. Spurious velocities can be
reduced of about an order of magnitude with respect to standard discretization
procedure.Comment: Final version, to appear in Phys. Rev.
Self-attractive semiflexible polymers under an external force field
The dynamical response of a tethered semiflexible polymer with
self-attractive interactions and subjected to an external force field is
numerically investigated by varying stiffness and self-interaction strength.
The chain is confined in two spatial dimensions and placed in contact with a
heat bath described by the Brownian multiparticle collision method. For strong
self-attraction the equilibrium conformations range from compact structures to
double-stranded chains, and to rods when increasing the stiffness. Under the
external field at small rigidities, the initial close-packed chain is
continuously unwound by the force before being completely elongated. For
double-stranded conformations the transition from the folded state to the open
one is sharp being steeper for larger stiffnesses. The discontinuity in the
transition appears in the force-extension relation as well as in the
probability distribution function of the gyration radius. The relative
deformation with respect to the equilibrium case along the direction normal to
the force is found to decay as the inverse of the applied force.Comment: Accepted for publication in Polymer
Lattice Boltzmann study of chemically-driven self-propelled droplets
We numerically study the behavior of self-propelled liquid droplets whose
motion is triggered by a Marangoni-like flow. This latter is generated by
variations of surfactant concentration which affect the droplet surface tension
promoting its motion. In the present paper a model for droplets with a third
amphiphilic component is adopted. The dynamics is described by Navier-Stokes
and convection-diffusion equations, solved by lattice Boltzmann method coupled
with finite-difference schemes. We focus on two cases. First the study of
self-propulsion of an isolated droplet is carried on and, then, the interaction
of two self-propelled droplets is investigated. In both cases, when the
surfactant migrates towards the interface, a quadrupolar vortex of the velocity
field forms inside the droplet and causes the motion. A weaker dipolar field
emerges instead when the surfactant is mainly diluted in the bulk. The dynamics
of two interacting droplets is more complex and strongly depends on their
reciprocal distance. If, in a head-on collision, droplets are close enough, the
velocity field initially attracts them until a motionless steady state is
achieved. If the droplets are vertically shifted, the hydrodynamic field leads
to an initial reciprocal attraction followed by a scattering along opposite
directions. This hydrodynamic interaction acts on a separation of some droplet
radii otherwise it becomes negligible and droplets motion is only driven by
Marangoni effect. Finally, if one of the droplets is passive, this latter is
generally advected by the fluid flow generated by the active one.Comment: 14 pages, 9 figures. In press on EPJ
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