| Wed April 6th 2011 16:00 ZH286 | Seminar | Clustering and Lagrangian statistics of Light particles in Turbulence Julián Martínez Mercado, Vivek Nagendra Prakash |
Details:Multi-phase flows where the carrier fluid transports particles under turbulent conditions play an important role in nature and in industrial applications. A thorough understanding of the dynamics of particles (light, neutral or heavy) in turbulent flows and their clustering behavior is therefore crucial. In these particle-laden flows, the particles have finite sizes and their densities can be different from that of the carrier fluid. Thus, the particle dynamics and clustering behavior are expected to be different compared to neutral fluid tracers. In this context, two relevant parameters are the density ratio (a ratio of the fluid and particle density), and the Stokes number (a ratio of the particle's response time to the typical time scale of the smallest eddies in the turbulent flow).We study the Lagrangian velocity and acceleration statistics of light particles (bubbles in water) in homogeneous isotropic turbulence. We study the effect of density ratio on the Lagrangian statistics using micro-bubbles (of size comparable to the Kolmogorov length scale, St ~ O(0.01)) dispersed in a turbulent flow. The trajectories of the micro-bubbles are obtained using 3D Particle Tracking Velocimetry (PTV) experiments in the Twente water tunnel at different Re. It is found that the micro-bubble acceleration PDF has stretched exponential tails with higher intermittency than fluid tracers, consistent with DNS simulations of light particles in turbulence. Preliminary results on the effects of finite size on Lagrangian statistics using ‘inertial bubbles’ (10 times the size of Kolmogorov length scale, St ~ O(1)) will also be presented. For inertial bubbles, we find that the acceleration PDF has lesser intermittency compared to neutrally buoyant particles with finite size from numerics. The clustering behavior of inertial particles (heavy, neutral and light) in homogeneous isotropic turbulence is studied by applying 3D Voronoi analysis. We study the clustering of particles with d | ||
