On the significance of two-way coupling in simulation of turbulent particle agglomeration

Abstract

A study is reported that examines computations of turbulent particle agglomeration with one-way and two-way phase coupling for cases with small overall particle concentration. The fluid flow was computed using a direct numerical computation using the point-force approximation for particle-induced body force, and a soft-sphere, adhesive discrete-element method was used to simulate the particulate transport and agglomerate formation. Computations were performed with different values of the Stokes number and the adhesion parameter. A variety of measures were used to examine both the effect of particle agglomeration on the fluid turbulence and the structure and flow field within the particle agglomerates. It was found that agglomeration has little influence on the attenuation of turbulence by the particles, at least in the range of Stokes numbers examined in the paper. Computations with two-way coupling generated agglomerates that were larger and contained more particles than those for one-way coupling. The agglomerate structure for both one-way and two-way coupling cases had a fractal structure with a similar value of the fractal dimension. As the agglomerate size increased, the fluid motion inside the agglomerates was found to become increasingly correlated to the agglomerate velocity, acting to decrease the relative velocity and shear stress of the inner particles within the agglomerate.