Finite-size particles interacting with non-homogeneous turbulence

分散的两相流出现在许多工业应用和自然现象中，从海洋中的塑料运输到发动机中的喷雾。塑性输运预测或推进的效率和环境影响取决于预测和控制受重力和湍流联合作用的含重颗粒流的能力。小于最小流动长度尺度的惯性粒子的湍流输运已经得到了广泛的研究，但对于密度比流体略大且存在重力的有限大小粒子的情况，研究的程度要小得多，因此仍然存在大量悬而未决的问题：载流湍流如何影响中等质量的有限大小粒子的运动？它们是如何沿着它们的轨迹对湍流速度场进行采样的，它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，它们是如何影响载流子湍流的？这些知识差距目前阻碍了用于工程目的的预测模型的进一步发展。本项目拟结合前沿实验技术和全分辨直接数值模拟研究这些效应，将两种方法的优点结合起来：在实验中覆盖大范围的参数和部分信息，而在较少数量的全耦合数值模拟中提供全部信息。这将允许在粒子周围的近场研究从系统大小到非常小的尺度的动力学，并清楚地解释能量平衡。这种方法将使数据首次覆盖更广的参数空间（粒度、密度比、伽利略和雷诺数、固体体积分数）。这些结果有望大大提高我们对粒子-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.