Reducing Data Resolution for Better Superresolution: Reconstructing Turbulent Flows from Noisy Observation.

A superresolution (SR) method for the reconstruction of Navier-Stokes (NS) flows from noisy observations is presented. In the SR method, first the observation data are averaged over a coarse grid to reduce the noise at the expense of losing resolution and, then, a dynamic observer is employed to reconstruct the flow field by reversing back the lost information. We provide a theoretical analysis, which indicates a chaos synchronization of the SR observer with the reference NS flow.

Dynamics of inert spheres in active suspensions of micro-rotors.

Inert particles suspended in active fluids of self-propelled particles are known to often exhibit enhanced diffusion and novel coherent structures. Here we numerically investigate the dynamical behavior and self-organization in a system consisting of passive and actively rotating spheres of the same size. The particles interact through direct collisions and the fluid flows generated as they move.

Collective dynamics in a binary mixture of hydrodynamically coupled microrotors.

We study, numerically, the collective dynamics of self-rotating nonaligning particles by considering a monolayer of spheres driven by constant clockwise or counterclockwise torques. We show that hydrodynamic interactions alter the emergence of large-scale dynamical patterns compared to those observed in dry systems. In dilute suspensions, the flow stirred by the rotors induces clustering of opposite-spin rotors, while at higher densities same-spin rotors phase separate.

Rheology and ordering transitions of non-Brownian suspensions in a confined shear flow: effects of external torques.

We investigate the effect of an external torque, applied in the vorticity direction, to particles in a sheared non-Brownian suspension confined by rigid walls. At volume fractions of ϕ=0.48-0.

Ordering transition of non-Brownian suspensions in confined steady shear flow.

We report on ordering transitions of concentrated non-Brownian suspensions confined by two parallel walls under steady shear. At a volume fraction as low as ϕ=0.48, particles near the wall assemble into strings which are organized as a simple hexagonal array by hydrodynamic interactions.

Behavior of heavy particles in isotropic turbulence.

The motion of heavy particles in isotropic turbulence is investigated using direct numerical simulation. The statistics related to the velocity and acceleration of heavy particles for a wide range of Stokes numbers, defined as the ratio of the particle response time to the Kolmogorov time scale of turbulence (St=tau_{p}/tau_{eta}) , are investigated. A particular emphasis is placed on the statistics of the fluid experienced by heavy particles, which provide essential information on the dispersion of these particles.

Intermittent nature of acceleration in near wall turbulence.

Using direct numerical simulation of a fully developed turbulent channel flow, we investigate the behavior of acceleration near a solid wall. We find that acceleration near the wall is highly intermittent and the intermittency is in large part associated with the near wall organized coherent turbulence structures. We also find that acceleration of large magnitude is mostly directed towards the rotation axis of the coherent vortical structures, indicating that the source of the intermittent acceleration is the rotational motion associated with the vortices that causes centripetal acceleration.