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

本研究的目的是建立分散颗粒多相湍流大涡模拟（LES）模型，并利用数值模拟对其进行评价和优化。对于多相流的建模，采用气泡运动的直接数值模拟（DNS）来评估气泡运动对流体流动和气泡间相互作用的影响。研究了小固体颗粒对湍流的影响。为了评估粒子在LES中的运动公式，通过数值试验比较了拉格朗日方程和统计平均方程。在前一模型的基础上发展了LES的数值计算方法。利用DNS数据和可视化实验技术，从颗粒和流体流动的角度验证了这些结果。对于混合层、射流、通道流等基本流动，从层流到湍流，对上述模型和方法进行了检验，得出了气泡流动和载颗粒气流的普遍信息：a)粒子大小对气泡运动的影响可以通过LES分析，包括气泡运动的精确模型及其对体积平均方程的贡献。b)固体分散颗粒的湍流耗散可以用包含颗粒-流体相互作用的亚网格尺度模型来评价，而网格尺度模型对颗粒-流体相互作用的模拟效果较差。这些结果验证了LES对分散颗粒多相流的可行性，并表明在粒子-流体相互作用的建模和优化中应考虑湍流和颗粒运动的时间和空间尺度。

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.