Finite-size particles interacting with non-homogeneous turbulence

分散两相流存在于许多工业应用和自然现象中，从塑料在海洋中的运输到发动机中的喷雾。塑料输送的预测或推进的效率和对环境的影响取决于预测和控制含有重颗粒的流动的能力，这些流动服从重力和湍流的共同作用。人们对小于最小流动长度尺度的惯性粒子的湍流输运进行了广泛的研究，但对密度略大于流体的有限尺寸粒子在重力作用下的研究程度要小得多，因此仍然存在许多悬而未决的问题：载流湍流如何影响中等重的有限尺寸粒子的运动？他们如何采样沿其轨迹的湍流速度场，以及他们的沉降速度是多少？它们是否形成团簇，当它们的浓度增加时，它们对载流子湍流有何影响？这些知识差距目前阻碍了为工程目的建立预测模型的进一步进展。本项目建议用前沿的实验技术和完全分辨的直接数值模拟来研究这些影响，以结合这两种方法的优点：在实验中用部分信息覆盖大范围的参数，而用较少的全耦合数值模拟来提供全部信息。这将允许研究从系统大小到粒子周围近场的非常小的尺度的动力学，并清楚地解释能量平衡。这一方法将使数据首次覆盖较宽的参数空间(颗粒大小、密度比、伽利略和雷诺数、固体体积分数)。这一结果可望极大地促进我们对颗粒-湍流相互作用动力学的认识和建模。

Dispersed two-phase flows occur in many industrial applications and natural phenomena, ranging from plastic transported in oceans, to sprays in engines. Plastic transport prediction or efficiency and environmental impact of propulsion depend on the ability to predict and control flows containing heavy particles which are submitted to the combined action of gravity and turbulence. The turbulent transport of inertial particles smaller than the smallest flow length-scale has been widely investigated, but the case of finite-size particles with density moderately larger than the fluid and in the presence of gravity has only been explored to a much lesser extent, so that a significant number of open questions remain: how does the carrier flow turbulence affect the motion of moderately heavy, finite-size particles? How do they sample the turbulent fluid velocity field along their trajectory, and what is their settling velocity? Do they form clusters, and how do they affect the carrier turbulence when their concentration increases? These knowledge gaps are currently blocking further progress towards predictive models for engineering purposes. The present project proposes to study these effects with cutting-edge experimental techniques and fully resolved direct numerical simulation to combine the advantages of the two approaches: covering a wide range of parameters with partial information in experiments with a smaller number of fully coupled numerical simulations providing full information. This will allow to investigate dynamics from the system size down to the very small scales in the near-field around the particles with clear interpretation of the energy balance. This approach will lead to data covering for the first time a wide parameter space (particle size, density ratio, Galileo and Reynolds numbers, solid volume fraction). The results can be expected to advance our knowledge and the modelling of the dynamics of particle-turbulence interaction significantly.