Coagulation-induced particle-concentration fluctuations in homogeneous, isotropic turbulence

The turbulent coagulation of micron-sized colloidal particles in a liquid is controlled by the shearing motion produced by Kolmogorov scale eddies. The rate of energy dissipation has fluctuations which vary over the integral length and time scale in a homogeneous, isotropic turbulent flow. We present a model of the particle concentrations and coagulation rates in a set of fluid packets that are large compared with the Kolmogorov scale and small compared with the integral scale. Particle coagulation occurs rapidly in regions of the flow with large dissipation rates, leading to a depletion of singlet particles. Thus, the singlet number density is negatively correlated with the shear rate. Turbulent mixing mitigates these concentration variations and the particle concentration field becomes nearly uncorrelated with dissipation rate in very dilute suspensions with fRl!1. Here, f is the particle volume fraction and Rl is the Reynolds number based on the Taylor microscale. A simulation of a suspension of coalescing drops shows that the imperfect mixing at finite fRl broadens the drop size distribution. © 2002 American Institute of Physics. @DOI: 10.1063/1.1478562#