Multiscale Simulations of Multiphase Systems

多相系统的多尺度模拟

• 批准号: 0522581
• 负责人: Gretar Tryggvason
• 金额: $ 4万
• 依托单位: Worcester Polytechnic Institute
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-09-01 至 2006-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0522581&HistoricalAwards=false
• 关键词: Multiscale; Simulations; Multiphase; Systems

ABSTRACT - 0522581Worcester Polytechnic InstituteDirect Numerical Simulations (DNS) of multiphase flows, where all continuum scales of the flow are fully resolved, have progressed enormously in the last few years. Increase in computer power and new algorithms now make it possible to follow the unsteady motion of several hundred particles (drops, bubbles and solids) for long enough times so that meaningful averages for the fluid mixture can be calculated. However, in spite of the enormous information and understanding that DNS are providing for relatively complex flows, real systems provide challenges that still limit the range of systems that can be simulated, even when we limit our studies to systems well described by continuum theories. The problem is, as one might expect, one of scale. Starting with simulations where what we might call the ''dominant small-scales'' are fully resolved, it is frequently found that multiphase flows also can generate features much smaller than the dominant flow scales, consisting of very thin films, filaments, and drops. Frequently there is a clear separation of scales between these ''features,'' usually inertia effects are relatively small for the local evolution, and in isolation these features are often well described by analytical models. It is proposed here to develop an approach to incorporate such small-scale features as models into numerical simulations of multiphase flows. The development will consist of both a theoretical framework and an implementation into a numerical method. The other problem that will be addressed here, although at a more exploratory level, is how to use the results of DNS of multiphase flows for engineering models of such flows. Considerable progress has been made in the modeling of disperse flows using the so-called two-fluid model, but much less has been achieved for flows with where each phase consists of both a continuous and a disperse part. In general, modeling of the averaged properties of multiphase flows lags far behind what has been achieved homogeneous turbulent flows, but the recent progress in DNS of multiphase flows makes it urgent to advance such modeling. These approaches will be developed in the context of a physical system that usually exhibits considerable complexity, and that is of immense practical importance. Atomization of liquids is found in a multitude of applications and while computational modeling of sprays has reached a fairly high degree of sophistication, such models all rely on very crude approximations for the initial atomization. As the initial droplet size distribution is generally critical for the subsequent evolution of the drops, the lack of understanding of the atomization is a major bottleneck for computations of sprays.The intellectual merit of the proposed activity lies in the advancement of the capabilities to conduct numerical simulations of multiphase flows and the use of these capabilities to provide greatly improved understanding of atomization. The broader impact of the study proposed here are two-fold. First of all, it will help redefine the state of the art in multiphase flow studies by demonstrating how computations can be used to examine much more complex problems that have been attempted until now. Secondly, it will also help train graduate students in the use of DNS for multiphase flows.

多相流的直接数值模拟（DNS）在过去的几年里取得了巨大的进展，它可以完全解决流动的所有连续尺度。现在，计算机能力的提高和新的算法使得对几百个粒子（水滴、气泡和固体）的不稳定运动进行足够长时间的跟踪成为可能，这样就可以计算出流体混合物的有意义的平均值。然而，尽管DNS为相对复杂的流提供了大量的信息和理解，但实际系统提供的挑战仍然限制了可以模拟的系统的范围，即使我们将研究限制在连续统理论所描述的系统中。正如人们所预料的那样，问题在于规模。从我们称之为“优势小尺度”的模拟开始，我们经常发现多相流也可以产生比优势流尺度小得多的特征，包括非常薄的薄膜、细丝和液滴。通常在这些“特征”之间存在明显的尺度分离，通常惯性效应对于局部进化来说相对较小，并且在孤立的情况下，这些特征通常被分析模型很好地描述。本文建议发展一种方法，将模型等小尺度特征纳入多相流的数值模拟中。开发将包括理论框架和数值方法的实现。这里要讨论的另一个问题是，如何将多相流的DNS结果用于此类流的工程模型，尽管这是一个更具探索性的问题。在用所谓的双流体模型模拟分散流动方面已经取得了相当大的进展，但是对于每个相都由连续部分和分散部分组成的流动来说，取得的进展要少得多。一般来说，多相流的平均性质的建模远远落后于均匀湍流的建模，但多相流的DNS的最新进展使得这种建模迫在眉睫。这些方法将在通常表现出相当复杂性的物理系统的背景下开发，这具有巨大的实际重要性。液体雾化在许多应用中都有发现，虽然喷雾的计算建模已经达到了相当高的复杂程度，但这些模型都依赖于非常粗糙的初始雾化近似。由于初始液滴尺寸分布通常对液滴的后续演变至关重要，因此缺乏对雾化的理解是雾滴计算的主要瓶颈。所提出的活动的智力价值在于提高了多相流的数值模拟能力，并利用这些能力大大提高了对雾化的理解。这里提出的研究的更广泛影响是双重的。首先，它将通过展示如何使用计算来检查迄今为止已经尝试过的更复杂的问题，从而帮助重新定义多相流研究的艺术状态。其次，它也将有助于培训研究生在多相流中使用DNS。