17 research outputs found
Phase separating binary fluids under oscillatory shear
We apply lattice Boltzmann methods to study the segregation of binary fluid
mixtures under oscillatory shear flow in two dimensions. The algorithm allows
to simulate systems whose dynamics is described by the Navier-Stokes and the
convection-diffusion equations. The interplay between several time scales
produces a rich and complex phenomenology. We investigate the effects of
different oscillation frequencies and viscosities on the morphology of the
phase separating domains. We find that at high frequencies the evolution is
almost isotropic with growth exponents 2/3 and 1/3 in the inertial (low
viscosity) and diffusive (high viscosity) regimes, respectively. When the
period of the applied shear flow becomes of the same order of the relaxation
time of the shear velocity profile, anisotropic effects are clearly
observable. In correspondence with non-linear patterns for the velocity
profiles, we find configurations where lamellar order close to the walls
coexists with isotropic domains in the middle of the system. For particular
values of frequency and viscosity it can also happen that the convective
effects induced by the oscillations cause an interruption or a slowing of the
segregation process, as found in some experiments. Finally, at very low
frequencies, the morphology of domains is characterized by lamellar order
everywhere in the system resembling what happens in the case with steady shear.Comment: 1 table and 12 figures in .gif forma
Ordering of the lamellar phase under a shear flow
The dynamics of a system quenched into a state with lamellar order and
subject to an uniform shear flow is solved in the large-N limit. The
description is based on the Brazovskii free-energy and the evolution follows a
convection-diffusion equation. Lamellae order preferentially with the normal
along the vorticity direction. Typical lengths grow as (with
logarithmic corrections) in the flow direction and logarithmically in the shear
direction. Dynamical scaling holds in the two-dimensional case while it is
violated in D=3
Plasma Diagnostics of the Interstellar Medium with Radio Astronomy
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