Effects of the Density Ratios to the Behaviors of Small Bubbles and Particles in Isotropic Homogeneous Turbulence.

Abstract

The effects of particle density on turbulence statistics, such as the preferential concentration and the particle dispersion, are numerically investigated for various Stokes numbers. The small particle motions in isotropic homogeneous turbulent flow are simulated by the one-way coupling method. In the present method, the fluid and particle phases are solved in the Eulerian and Lagrangian ways, respectively. The preferential concentration for zero-density particles, (i.e. corresponding to the contaminated bubble limit), is much stronger than that for the heavier particles. The root-mean-square velocity of the particle versus the Stokes number is analyzed through the comparison of the Tchen's theory (Hinze, 1975). The υ rms profile for the heavier particles shows good agreement with that of the Tchen's theory, while that for the bubbles shows considerable difference from the theory due to the strong preferential concentration. The dispersion coefficient of particle is also investigated. At the Stokes numbers, such that the preferential concentration occurs, Dp for the heavier particles is larger than the dispersion coefficient of fluid Df, while Dp for bubbles is smaller than Df. The difference between Dp and Df for the bubbles is much larger than that for the heavier particles.