Wed July 6th 2016 16:30 – 17:00 ZH286 | Seminar | Dynamics of buoyant particles in turbulent flows Varghese Mathai |

## Details:Particle-suspensions in turbulent flows occur in a range of natural and industrial settings. In many situations, these particles have a density different from that of the carrier fluid. This density difference can affect the way these particles move through flows, which can change the drag as well as transport of various quantities in multiphase systems. In this study, we use particle-tracking techniques to study the dynamics of light (buoyant) particles in a homogeneous isotropic turbulent flow. We first consider buoyant spheres of finite-size (particle size is large compared to the turbulent flow length-scales). Buoyancy is shown to produce interesting variability in the motion of these particles, and these motions dominate over the background turbulence-induced effects even at marginal density differences. Next, we consider a tiny buoyant particle (a micro-bubble), with a very small Stokes number (St), signifying the particleâ€™s response-time in the flow. We address the question: Can a small particle with a very small Stokes number be regarded a good tracer a flow? Our analysis shows that gravity can lead to the modification of both vertical and horizontal acceleration statistics, and these occur despite the small size and minute St of these particles. We theoretically predict this gravity effect for developed isotropic turbulence, with the ratio of Stokes to Froude number or equivalently the particle drift-velocity governing the extent of deviation from ideal tracer particles. |