The effect of suspended particles on Rayleigh-Bénard buoyant thermal convection

悬浮颗粒流动在自然和技术系统中广泛存在，如流态化床、太阳能集热器、化学处理、雨水形成、悬浮晶体岩浆和许多其他系统。然而，他们的计算研究一直受到所需模拟固有复杂性的限制。特别是，人们对颗粒流中的热传递知之甚少。本项目解决了这一大类中的一个典型问题，即悬浮粒子对浮力瑞利-伯纳德热对流的影响，即流体层中的流动从下面加热，从上面冷却。这个问题的无粒子版本一直是广泛研究的主题，因为它在物理学和工程学的许多分支中处于中心地位，但粒子的影响几乎没有被触及。这里提出的工作试图通过确定颗粒自然对流中的重要流动模式和量化颗粒引入的热传递修正来回答基本问题。这项研究将影响常用的工业或地球物理模拟中使用的湍流和热传输模型，包括大气、海洋、地核和气候的模型。它还有可能帮助开发可再生能源，如基于太阳能集热器和氢气生产的能源。为了提高我们对颗粒热传递的认识，拟议的工作将利用越来越逼真和复杂的模型。对Rayleigh-Bénard稳定性的简化线性分析将提供基本控制参数的影响方向，如颗粒与流体的密度和热容比、流体普朗特数以及质量和热负荷。点粒子模型将被用来阐明参数空间中的区域，在这些区域中，在湍流区域中，热传递有望发生实质性的改变。该项目的高潮在于使用数值方法Physalis进行完全解析的颗粒模拟，该数值方法在高度优化的多GPU代码中实现，该代码能够解析数千个悬浮颗粒的流动。这样，颗粒-流体的动量和热交换就可以从第一原理计算出来，避免了点-粒子模型所必需的特殊的参数化。这些模拟将集中于简化模型发现的特别感兴趣的情况，并将允许更详细和更深入地了解影响中涉及的物理，如传热增强和粒子聚集等。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Flows with suspended particles are widespread in natural and technological systems such as fluidized beds, solar collectors, chemical processing, rain formation, magmas with suspended crystals and many others. However, their computational study has been limited by the inherent complexity of the simulations required. In particular, little is known about heat transfer in particulate flows. The present project addresses a canonical problem in this broad class, namely the effect of suspended particles on buoyant Rayleigh-Bénard thermal convection, the flow in a fluid layer heated from below and cooled from above. The particle-free version of this problem has been the subject of extensive studies due to its centrality in many branches of physics and engineering, but the effect of particles has barely been scratched. The work proposed here seeks to answer fundamental questions by identifying the significant flow regimes in particulate natural convection and quantifying the heat transfer modifications that particles introduce. This research will influence turbulence and heat transfer models used in common industrial or geophysical simulations, including those of the atmosphere, the oceans, the earth core and climate. It also has the potential to help the development of renewal energy sources, such as those based on solar collectors and hydrogen production. To advance our knowledge of particulate heat transfer, the proposed work will make use of models of increasing realism and complexity. A simplified linear analysis of Rayleigh-Bénard stability will provide an orientation on the effect of basic control parameters such as the particle-to-fluid density and heat capacity ratios, the fluid Prandtl number, and the mass and thermal loading. The point-particle model will be used to elucidate the regions of parameter space where heat transfer can be expected to be substantially modified in the turbulent regime. The culmination of the project consists in fully resolved particulate simulations using the numerical method Physalis, implemented in a highly-optimized multi-GPU code, which is able to resolve flows with many thousands of suspended particles. In this way the particle-fluid momentum and heat exchanges can be calculated from first principles avoiding the ad hoc parametrization necessary with the point-particle model. These simulations will be focused on situations of particular interest uncovered by the simplified models and will permit a much more detailed and deeper understanding of the physics involved in effects such as heat transfer enhancement and particle clustering, among others.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.