| Tue January 10th 2017 16:00 – 17:00 ZH286 | Seminar | Preferential concentration of inertial particles in turbulent flows Mickaël Bourgoin |
Details:Particle-laden flows are of relevant interest in many industrial and natural systems. When the carrier flow is turbulent, a striking phenomenon occurs, where particles with inertia tend to segregate in clusters, also leading to depleted regions. This mechanism, called preferential concentration, results from the interaction of the particles with the multi-scale and random structure of turbulence. The exact mechanism at play and the full dynamical consequences still remain however to be unveiled. This lecture will be devoted to recent experimental investigations of clustering of small water droplets in homogeneous and isotropic active-grid-generated turbulence. We investigate the effects of Reynolds number (Reλ, quantifying the turbulence intensity) and particles Stokes number (St, quantifying particles inertia) on preferential concentration. Using Voronoï tesselations, we characterise clustering level and cluster properties (geometry, typical dimensions and fractality). We will show that the exact same Voronoï analysis can be applied to investigate clustering properties of specific topological points of the velocity field of single phase homogeneous isotropic turbulence (obtained for instance from direct numerical simulations) in order to explore the relevance of possible clustering mechanisms, such as centrifugal effects (heavy particles sampling preferentially low-vorticity regions) and sweep-stick mechanisms (heavy particles preferentially sticking to low-acceleration points). | ||
