Inertial effects in dusty Rayleigh–Taylor turbulence

We investigate the dynamics of a dilute suspension of small, heavy particles superposed on a reservoir of still, pure fluid. The study is performed by means of numerical simulations of the Saffman model for a dilute particle suspension (Saffman, J. Fluid Mech., vol. 13, issue 1, 1962, pp. 120–128). In the presence of gravity forces, the interface between the two phases is unstable and evolves in a turbulent mixing layer which broadens in time. In the case of negligible particle inertia, the particle-laden phase behaves as a denser fluid, and the dynamics of the system recovers to that of the incompressible Rayleigh–Taylor set-up. Conversely, particles with large inertia affect the evolution of turbulent flow, delaying the development of turbulent mixing and breaking the up–down symmetry within the mixing layer. The inertial dynamics also leads to particle clustering, characterised by regions with higher particle density than the initial uniform density, and by the increase of the local Atwood number.

Velocity measurements of dilute suspensions over and through various porous media models

This study is focused on the motion of a dilute suspension containing rigid, spherical, non-Brownian, noncolloidal particles flowing over and through porous media models. The flow is confined to very low Reynolds numbers. To examine the velocity distribution particle image velocimetry (PIV) was applied in conjunction with refractive index matching (RIM) techniques. This study is the first of its kind analyzing the interaction between two common engineering systems: suspension fluid and porous media.

Self-diffusion in nanofluids of nonelongated particles in the dilute limit

The dynamic features of a dilute suspension of nanoparticles (nanofluid) are fully modified depending on the dominant particles slip mechanism acting in the suspension. Self-diffusion effects in highly sheared diluted suspensions (entrance conditions and microapplications) can lead to a particles distribution fully different from the bulk one. The reported investigation proposes a model to determine the self-diffusion of three-planes symmetric nonelongated particles inmersed in a sheared Stokes flow. The model is based on the real displacements between any pair of particles and an statistical approach to determine contact kinematic irreversibilities. According to the proposed model, the source of hydrodynamic irreversibility is closely related to the particles shape. This is clearly demonstrated through the application of the model to cubic particles. The main conclusion is that the particles shape plays a significant role in the dynamic behavior of the suspension and, as a result, in the self-diffusion coefficient. The reported results arising from the cubic particles trajectories in a Stokes flow are reasonably close to the ones reported by Brady and Morris (J Fluid Mech, 348:103–139, 1997) for suspensions under high Pe number, and Zarraga and Leighton (Phys Fluids 13(3):565-577, 2001).

Shear driven vorticity aligned flocs in a suspension of attractive rigid rods

A combination of rheology, optical microscopy and computer simulations was used to investigate the microstructural changes of a semi-dilute suspension of attractive rigid rods in an imposed shear flow.