Study of the Equation of Motion for Solid Particles in Turbulent Flows

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The goal of our study is to develop the large-eddy simulation (LES) method for particle-laden flows. To this end, both of the subgrid scale (SGS) model and the equation of particle motion should be improved. Particular attention was focused on the latter topic in this project. The fluid forces on particle have usually been modeled by the measurement for particle fixed in a stream but they might differ from the actual ones on free particles. To assess the difference in between, we developed a numerical scheme to resolve the flow around fixed/moving particles since the simultaneous measurement of trajectory and force is difficult by experiment. In addition, we applied our method to particle-laden flows to investigate the interaction between particle motion and fluid turbulence.Major results and findings are summarized as follows. (1) We made various database for flow around fixed/moving particles in a uniform stream, flow around particles in a disturbed flows, homogeneous flow including solid particles, and wall bounded flow with solid particles. (2) The difference in fluid forces for a fixed particle and a released one is systematically analyzed. Namely, the drag force is slightly increased while the fluctuation of lift force is drastically reduced for a released one. This suggests the prediction of particle distribution based on the fluid force on fixed particle is misleading. (3) The average drag on particles is different from that on a particle moving individually, when particles form clusters. In addition, particle clusters have life cycles affected by the interaction with fluid turbulence they caused. (4) On the basis of above-mentioned results, we proposed an SGS kinetic energy model considering the energy production due to particle wakes and the modulation in energy dissipation due to the particle distances.