A HOLISTIC FRAMEWORK FOR HYBRID MODELLING OF SOLID-LIQUID FLOWS

固液悬浮液在管道和容器中的运动是一个普遍存在的复杂问题，具有商业挑战性和重要的技术意义。工业应用很多，例如化工、消费品、食品、制药、石油、采矿、河流工程、建筑、发电、生物技术和生物医学。尽管市场如此庞大，但由于严重缺乏对这些流动的根本了解，工业实践和流程既不高效，也不是最佳的。这种流动涉及各种尺度上的复杂现象，因为流动管道通常从微米尺度到厘米尺度不等，而容器从毫升尺度到立方米尺度不等。流动可能是湍流或粘性的，载体流体可能表现出复杂的非牛顿流变性。颗粒以不同的形状、大小、密度、体积和表面性质存在，这加剧了问题的复杂性。输送或处理固液悬浮液的工艺设计需要有关颗粒行为的信息，如颗粒轨迹、流线上的径向迁移、颗粒速度分布和固体分布。然而，由于几乎没有可用的仪器可用，在对固液流动成像和测量局部流体和固体速度方面存在巨大的实际困难。有实际意义的混合物通常是浓缩的和不透明的，因此流动可视化是不可能的，并且颗粒可能是可变形的、可破碎的或容易聚集的。这种复杂的现象目前很难预测。这项建议将使用多尺度方法来研究固液悬浮液的流动，包括具有复杂非牛顿流变性的流体和具有复杂性质的颗粒：(I)实验上通过正电子发射粒子跟踪的独特而准确的拉格朗日技术，该技术可以测量不透明系统中的局部三维相速度和相分布；以及(Ii)通过开发和验证新的建模方法来预测这种流动，包括颗粒、流体和壁面之间的详细相互作用。许多先进的建模技术将被使用，主要包括离散单元法(DEM)、计算流体动力学(CFD)、光滑粒子流体动力学(SPH)、格子Boltzmann方法(LBM)和粗粒度分子动力学(CGMD)。然而，这些方法本身都不能有效地模拟这些复杂的流动，因为它们都有优点和缺点。因此，我们将利用每种技术的优势，以一种高效的混合方式组合这些方法，以产生一个集成的多尺度模块化框架，该框架将在唯一和著名的开放源代码DL_Meso中免费提供。因此，我们将评估最好的混合方法，并通过将模型混合与流动特性进行映射来开发用于模拟这些复杂流动的范例。使用混合模拟方法和多尺度方法来包括集中湍流、非牛顿流变学的流体、复杂形状和性质的颗粒将在模拟这些复杂流动方面产生巨大的飞跃。从中长期来看，这项工作的发现应该会提高英国固体-液体加工技术的竞争力。然而，我们的工业和学术合作伙伴将能够通过参与该项目立即获得好处。

The movement of solid-liquid suspensions in pipes and vessels is a generic complex problem which is commercially challenging and technically important. Industrial applications are numerous, e.g. chemicals, consumer goods, food, pharmaceuticals, oil, mining, river engineering, construction, power generation, biotechnology and biomedical. Despite such large markets, industrial practice and processes are neither efficient nor optimal because of a severe lack of fundamental understanding of these flows. Such flows involve complex phenomena on a wide range of scales as flow conduits generally vary from the micron scale to the centimetre scale, and vessels vary from the millilitre scale to the cubic metre scale. Flows may be turbulent or viscous and the carrier fluid may exhibit complex non-Newtonian rheology. Particles occur in various shapes, sizes, densities, bulk and surface properties which exacerbates the complexity of the problem.The design of processes for conveying or processing solid-liquid suspensions requires information about particle behaviour such as particle trajectory, radial migration across streamlines, particle velocity distribution, and solids distribution. There are, however, huge practical difficulties in imaging solid-liquid flows and measuring local fluid and solid velocities, since little of the available instrumentation is applicable. Mixtures of practical interest are often concentrated and opaque so that flow visualisation is impossible, and particles may be deformable, breakable or prone to aggregation. Such complex phenomena are presently difficult to predict. They have hampered fundamental research and the development of rigorous holistic modelling strategies and, as a result, work has generally followed a piecemeal empirical approach.This proposal will use a multiscale approach to study the flow of solid-liquid suspensions including fluids of complex non-Newtonian rheology and particles with complex properties: (i) experimentally via a unique and accurate Lagrangian technique of positron emission particle tracking, which can measure local 3-D phase velocities as well as phase distribution in opaque systems; and (ii) by developing and validating novel modelling approaches to predict such flows including detailed interactions between particles, fluid and walls. A number of advanced modelling techniques will be used including principally the Discrete Element Method (DEM), Computational Fluid Dynamics (CFD), Smooth Particle Hydrodynamics (SPH), Lattice Boltzmann Method (LBM) and Coarse-Grained Molecular Dynamics (CGMD).None of these methodologies on its own, however, is able to effectively model these complex flows as they all enjoy strengths as well as weaknesses. We will, therefore, exploit the strengths of each technique by assembling these methods in an efficient hybrid fashion to produce an integrated multiscale modular framework to be made available free of charge within the unique and well-known open source code DL_MESO. Thus, we will evaluate the best hybrid approaches and develop a paradigm for modelling these complex flows by mapping the model hybrids against flow characteristics.The use of a hybrid modelling methodology and a multiscale approach to include concentrated turbulent flows, fluids of non-Newtonian rheology, particles of complex shapes and properties will produce a quantum leap advance in the modelling of these complex flows. In the medium to long-term, the findings from this work should improve the competitiveness of the UK solid-liquid processing technologies. Our industrial and academic partners, however, will be able to draw immediate benefits through engagement with the project.