MoST-DFG Collaboration - Theoretical, numerical and experimental investigations of gravity-driven fluid-granular mixture flows

MoST-DFG 合作 - 重力驱动的流体-颗粒混合物流动的理论、数值和实验研究

• 批准号: 425259073
• 负责人: Professor Dr.-Ing. Yongqi Wang
• 金额: --
• 依托单位: Department of Mechanical Engeneering
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2023-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/425259073?language=en
• 关键词: MoST; DFG; Collaboration; Theoretical; numerical

Fluid-granular mixture flows are motivated by various applications in industrial processes and predictions of natural hazards such as debris flows. A debris flow represents a gravity-driven flow of sediment particles and water, which fills the interstices of granular material partially or excessively. Despite the past developments in modeling, computing and experimenting geophysical mass flows, the prediction of such fluid-granular multiphase flows is still a most challenging topic mainly in two aspects (i) theoretical and numerical modeling and (ii) experimental investigation. On the one hand, in most continuum models, such mixture flows are often treated as a single-phase medium, even though they are clearly two-phase mixture. In such single-phase approaches, the debris mixture is considered either as a non-Newtonian fluid including some plastic behavior or as a Coulomb continuum where the effect of the interstitial fluid is incorporated parametrically or as a mixture with the same constituent velocities. Very rarely multi-constituent mixture models are constructed and applied to debris flows. A few existing models consider such multiphase concepts as fluid-saturated granular mixtures, although natural granular flows are often not fully saturated or else over-saturated by water. On the other hand, the simultaneous measurement of velocities and volume fractions of all constituents in a fluid-granular mixture flow is also a difficult task. Although many experimental studies discuss the effect of the interstitial fluid on the granular flow, only the dynamics of the granular medium is measured, because of the difficulty in measuring the dynamics of the fluid phase in a granular-fluid mixture.With this project, we will attempt to develop a fluid-granular two-phase model, which is able to describe such under-saturated and over-saturated mixtures and their transition by means of a two-layer approach, in which the fluid-saturated granular lower layer is overlain by either the pure granular upper layer, for the under-saturated case, or the pure fluid, for the over-saturated case. For experimental investigations, the indirect image measurement technique will be developed, by coupling PIV and PTV, to measure the fluid velocities, the granular positions, velocities and volume fractions during the dynamic mixture flow. In this coupling method, PIV will be used for simultaneously measuring the fluid velocities, and PTV for measuring the velocities of granules. The benefits are that the accuracy of the PIV method is high for discriminating the seeding particles that identifying the fluid phase, while the PTV can offer more detailed information about granular velocities than PIV. The theoretical model will be examined numerically by the discontinuous Galerkin (DG) method of an arbitrary high-order accuracy in terms of gravity-driven flows of various under- or over-saturated granular-fluid mixtures and validated by experimental results.

流体-颗粒混合流动的动机是工业过程中的各种应用和对自然灾害（如泥石流）的预测。泥石流是一种由重力驱动的泥沙颗粒和水的流动，它部分或过度地填满颗粒物质的间隙。尽管过去在地球物理质量流的建模、计算和实验方面取得了进展，但这种流体-颗粒多相流的预测仍然是一个最具挑战性的课题，主要集中在两个方面(1)理论和数值模拟以及(2)实验研究。一方面，在大多数连续介质模型中，这种混合流通常被视为单相介质，尽管它们明显是两相混合。在这种单相方法中，碎屑混合物要么被视为包含某些塑性行为的非牛顿流体，要么被视为包含了间隙流体影响的库仑连续体，要么被视为具有相同组成速度的混合物。很少建立多组分混合模型并应用于泥石流。一些现有的模型考虑了流体饱和颗粒混合物等多相概念，尽管天然颗粒流通常不完全饱和或被水过度饱和。另一方面，同时测量流体-颗粒混合流中所有组分的速度和体积分数也是一项困难的任务。虽然许多实验研究讨论了间隙流体对颗粒流动的影响，但由于难以测量颗粒-流体混合物中流体相的动力学，因此只测量了颗粒介质的动力学。在这个项目中，我们将尝试开发一种流体-颗粒两相模型，该模型能够通过两层方法描述这种欠饱和和过饱和混合物及其过渡，其中流体饱和的颗粒下层被未饱和情况下的纯颗粒上层覆盖，或者纯流体覆盖，过饱和情况下。在实验研究方面，将发展PIV和PTV相结合的间接图像测量技术，以测量混合动力流动过程中的流体速度、颗粒位置、速度和体积分数。在这种耦合方法中，PIV将用于同时测量流体速度，PTV用于同时测量颗粒速度。PIV方法的优点是，在识别流体相的种子颗粒方面，PIV方法的准确性很高，而PTV可以提供比PIV更详细的颗粒速度信息。该理论模型将通过任意高阶精度的不连续伽辽金（DG）方法对各种欠饱和或过饱和颗粒流体混合物的重力驱动流动进行数值检验，并通过实验结果进行验证。