Development and evaluation of numerical method for large eddy simulation of multiphase turbulence flows

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An aim of this research was to develop models for a large eddy simulation (LES) of multiphase turbulence flow with dispersed particles and to evaluate and optimize them using numerical simulation. For modeling of multiphase flows, a direct numerical simulation (DNS) of bubble motions evaluated their effects on the fluid flow and the interaction between bubbles. Turbulence variation by small solid particles was also investigated. For evaluating a formulation of particle motions in the LES, a Lagrangian equation and a statistical averaged equation were compared by the numerical examinations. The numerical method of LES was developed based on the former model. These results were validated in views of the particles and the fluid flows using data of DNS and experiment with visualization techniques. For some basic flows, as mixing layers, jets, channel flows, the above models and the methods were examined in the range from laminar to turbulence, to indicate an universal information for the bubbly flow and the particle-laden air flow as follows,a) Particle size effects on the bubble motions by the buoyancy forces and the turbulence could be analyzed by the LES including the precise model of the bubble motion and its contribution to the volume averaged equation.b) The turbulence dissipation by the solid dispersed particles could be evaluated by a subgrid-scale model including the particle-fluid interaction, while a grid-scale interaction was not simulated by the present model effectively enough.These results validated the feasibility of LES to the dispersed-particle multiphase flows and indicated that the temporal and the spatial scales of the turbulence and the particle motion should be considered for the modeling of the particle-fluid interaction and its optimization.