A computational tool for particle-fluid flows

颗粒流体流动的计算工具

• 批准号: 0754344
• 负责人: Andrea Prosperetti
• 金额: $ 16万
• 依托单位: Johns Hopkins University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-04-15 至 2010-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0754344&HistoricalAwards=false
• 关键词: computational; tool; particle; fluid; flows

CBET-0754344ProsperettiIntellectual merit of the proposed activity. Flows with suspended particles arise frequently in Nature (e.g., dust storms, sediment transport, biological fluids), technology (e.g., pollutant transport, fluidized bed combustors, catalytic reactors, suspensions), and manufacturing (e.g. pharmaceutics, food processing, spray painting). Some of these flows are laminar (e.g. suspensions, slurries, monodisperse polymeric microspheres for diagnostic kit applications), but the particle volume fraction is large. More often they are turbulent and turbulence has a strong effect on the distribution and dispersion of the particles and, depending on conditions, the particles themselves can deeply change the turbulence character with respect to single-phase flow. Much effort has been devoted to the understanding of the nature of this so-called {\em two-way coupling} between fluid and particles by analysis, computation and experiment. Numerical simulation has proven particularly valuable in spite of many simplifications rendered necessary by the inherent complexity of these systems. Powerful techniques exist for dense suspensions in the Stokes flow regime. Turbulent flow simulations, on the other hand, have been conducted in conditions of exceedingly small particle concentration (particle volume fractions of the order of 10-4 or less) with the particles approximated as mass points moving under the action of approximately parameterized fluid forces. The action of the particles on the fluid has also mostly been approximated by superposing point forces. This procedure may be justified when the particle size is smaller than all the fluid length scales, including the Kolmogorov length. However, even in this case, the results are somewhat unsatisfactory as they rest on parameterized forces rather than forces obtained from first-principles calculations. More significantly, there are very many very important situations which cannot be studied by these means: particles suspended in a liquid, rather than a gas (e.g. sediments, chemical systems), non-dilute systems (e.g. fluidized beds), and many others. In recent NSF-supported work, a very efficient and accurate numerical method for the simulation of viscous incompressible fluid flows with thousands of suspended particles was developed by the proposer and his collaborators. The procedure fully accounts for the finite size of the particles, does not approximate their shape, and exactly satisfies the no-slip condition at the particle surface. The maximum particle Reynolds number depends on the grid resolution; with a very manageable resolution of 10 nodes per particle radius, Reynolds numbers up to a few tens can be handled. A particularly strong point of the method is the weak dependence of the computational time upon the number of particles suspended in the flow. This circumstance has permitted so far the simulation of flows with up to about 1000 suspended particles. In order to improve the resolution, be able to simulate a larger number of particles and more intense turbulence, it is necessary to develop new computational strategies: adaptive grids, algorithms with better scalability properties, efficient preconditioning etc. The work proposed here consists in: (1) The development of this enhanced code, its validation and some preliminary simulations (e.g., particles falling in an otherwise quiescent fluid, particles in decaying homogeneous isotropic turbulence), and (2) The use of modern software development methods and tools to permit the code to be readily used by others, making it freely available to the research community via a maintained web site with proper documentation, test cases, tutorials, detailed explanations etc.Broader impacts resulting from the proposed activity. As noted in the body of the proposal, the flow of fluids with suspended particles is one of the most active areas in contemporary fluid mechanics, with the relevant papers cited hundreds of times a year even many years after their publication. The code to be developed therefore meets a widely felt need in the research community which is ready to move away from simple models (point particles, Stokes flow, etc.) to finite particle Reynolds numbers, larger volume fractions and many particles. The availability of this computational tool will be a first step in the simulation of practical situations which lie at the heart of many problems of contemporary society such as energy (e.g.the oil industry, power generation, pollution), the environment (e.g. coastal erosion, precipitation) and life (e.g. pollen, grains, pharmaceuticals).

CBET-0754344繁荣拟议活动的智力优点。含有悬浮颗粒的流动经常出现在自然界(例如，沙尘暴、泥沙输送、生物流体)、技术(例如，污染物输送、沸腾床燃烧器、催化反应器、悬浮液)和制造(例如，制药、食品加工、喷漆)。其中一些流动是层流的(例如悬浮液、浆液、诊断试剂盒应用的单分散聚合物微球)，但颗粒体积分数很大。通常情况下，它们是湍流，湍流对颗粒的分布和扩散有很大的影响，根据条件的不同，颗粒本身可以深刻地改变相对于单相流的湍流特性。人们通过分析、计算和实验对流体和颗粒之间的这种所谓的双向耦合的本质进行了大量的研究。数值模拟已被证明特别有价值，尽管这些系统的固有复杂性使得许多简化是必要的。对于斯托克斯流区中的稠密悬浮，存在着强大的技术。另一方面，在颗粒浓度极小(颗粒体积分数约为10-4或更小)的条件下进行了湍流模拟，颗粒被近似为质点在近似参数化流体力的作用下运动。颗粒对流体的作用也主要是通过叠加的点力来近似的。当颗粒尺寸小于所有流体长度刻度(包括柯尔莫戈洛夫长度)时，这一过程可能是合理的。然而，即使在这种情况下，结果也有些不令人满意，因为它们依赖于参数化力，而不是从第一原理计算获得的力。更重要的是，有许多非常重要的情况不能用这些方法来研究：悬浮在液体中的颗粒，而不是悬浮在气体中的颗粒(例如沉积物、化学系统)、非稀释系统(例如流态床)以及许多其他情况。在最近由美国国家科学基金会支持的工作中，作者和他的合作者发展了一种非常有效和精确的数值方法来模拟含有数千个悬浮颗粒的粘性不可压缩流体流动。该方法充分考虑了颗粒的有限尺寸，不近似颗粒的形状，并且完全满足颗粒表面的无滑移条件。最大粒子雷诺数取决于网格分辨率；每粒子半径10个节点的分辨率非常易于管理，可以处理高达几十个节点的雷诺数。该方法的一个特别优点是计算时间对流动中悬浮颗粒数量的弱依赖性。到目前为止，这种情况已经允许模拟多达1000个悬浮颗粒的流动。为了提高分辨率，能够模拟更大数量的粒子和更强烈的湍流，有必要开发新的计算策略：自适应网格、具有更好可伸缩性的算法、有效的预处理等。这里建议的工作包括：(1)开发这种增强的代码、其验证和一些初步模拟(例如，落在静止流体中的粒子、衰变的各向同性湍流中的粒子)，以及(2)使用现代软件开发方法和工具来允许其他人容易地使用该代码，使其通过具有适当文档的维护的网站免费地提供给研究团体，测试用例、教程、详细说明等。建议活动产生的广泛影响。正如提案正文中指出的那样，含有悬浮颗粒的流体流动是当代流体力学中最活跃的领域之一，相关论文在发表多年后每年被引用数百次。因此，要开发的代码满足了研究界普遍感到的需求，即准备摆脱简单的模型(点粒子、斯托克斯流等)。到有限的粒子雷诺数、较大的体积分数和许多粒子。这一计算工具的提供将是模拟实际情况的第一步，这些实际情况是当代社会许多问题的核心，例如能源(例如石油工业、发电、污染)、环境(例如海岸侵蚀、降水)和生命(例如花粉、谷物、药品)。