70 research outputs found
Droplet breakup in homogeneous and isotropic turbulence
This fluid dynamics video shows the breakup of a droplet in a stationary
homogeneous and isotropic turbulent flow. We consider droplets with the same
density of the transporting fluid. The droplets and the fluid are numerically
modelled by means of a multicompo- nent Lattice-Boltzmann method. The turbulent
fluid is maintained through a large scale stirring force and the radius of
stable droplets, for the parameters in our simulation, is larger than the
Kolmogorov scale. Events of droplet deformation, break-up and aggregation are
clearly visible from the movie. With the present database droplet evo- lution
can be studied from both an Eulerian and Lagrangian point of view. The
Kolmogorov-Hinze criteria for droplets break-up can be tested also by means of
simulations with different viscosity contrast between the two components.Comment: 4 pages, 4 figures, 1 tabl
Statistically Steady Turbulence in Soap Films: Direct Numerical Simulations with Ekman Friction
We present a detailed direct numerical simulation (DNS) designed to
investigate the combined effects of walls and Ekman friction on turbulence in
forced soap films. We concentrate on the forward-cascade regime and show how to
extract the isotropic parts of velocity and vorticity structure functions and
thence the ratios of multiscaling exponents. We find that velocity structure
functions display simple scaling whereas their vorticity counterparts show
multiscaling; and the probability distribution function of the Weiss parameter
, which distinguishes between regions with centers and saddles, is in
quantitative agreement with experiments.Comment: 4 pages, 6 figure
Inertial particle acceleration in strained turbulence
The dynamics of inertial particles in turbulence is modelled and investigated
by means of direct numerical simulation of an axisymmetrically expanding
homogeneous turbulent strained flow. This flow can mimic the dynamics of
particles close to stagnation points. The influence of mean straining flow is
explored by varying the dimensionless strain rate parameter
from 0.2 to 20. We report results relative to the acceleration variances and
probability density functions for both passive and inertial particles. A high
mean strain is found to have a significant effect on the acceleration variance
both directly, through an increase in wave number magnitude, and indirectly,
through the coupling of the fluctuating velocity and the mean flow field. The
influence of the strain on normalized particle acceleration pdfs is more
subtle. For the case of passive particle we can approximate the acceleration
variance with the aid of rapid distortion theory and obtain good agreement with
simulation data. For the case of inertial particles we can write a formal
expressions for the accelerations. The magnitude changes in the inertial
particle acceleration variance and the effect on the probability density
function are then discussed in a wider context for comparable flows, where the
effects of the mean flow geometry and of the anisotropy at the small scales are
present
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