Stability Limits for Gas-Solid Suspensions with Finite Fluid Inertia using Particle-Resolved Direct Numerical Simulations

1134500PI：Subramaniam，Shanka技术用于从化石或生物燃料生产清洁能源并捕获由此产生的二氧化碳排放，使用的是沸腾床反应器，其颗粒大小和密度符合Geldart A和Geldart B分类。这些气固系统在颗粒尺度上表现出由流体动力不稳定性引起的非均匀和非均相流动结构。虽然对于Stokes流，均相气固悬浮液的稳定性已经有了理论上的估计，但有限流体惯性的范围还没有被探索。实施清洁能源技术的工业设备的设计和放大越来越依赖于计算流体动力学(CFD)模拟，这些模拟求解尚未经过测试的平均守恒方程。对平均多相流模型的一项重要验证测试是它们准确捕捉气固悬浮液稳定性极限的能力。由于光学通道的限制，很难从实验中获得数据，但粒子分辨直接数值模拟(DNS)可以提供充分表征的现场数据来揭示流动物理，并作为多相流模型对比评估的基准。本项目将采用第一性原理的方法来表征有限雷诺数下的气固悬浮液的稳定性极限。综合考虑体积分数波动和颗粒温度的影响，建立了气固悬浮液的综合稳定性理论。该项目的目标是：(I)量化Geldart B颗粒具有有限流体惯性的均匀气固悬浮液的稳定性极限；(Ii)利用集合论方法量化导致气固悬浮液中体积分数波动的颗粒-流体(流体动力学)和颗粒-颗粒相互作用的竞争机制；以及(Iii)了解Geldart A颗粒具有有限流体惯性的气固悬浮液的稳定性并表征其基本状态。考虑到体积分数波动的改进的集合论稳定性理论将为理解Geldart B和Geldart A悬浮液的动力学提供更多的洞察力，并将消除经典的比例分离假设。关于悬浮稳定性的DNS数据将提供给多相流社区，并将作为CFD程序的有用基准。DNS数据和稳定性理论也将对多相CFD代码的开发人员有用，例如国家能源技术实验室流行的多流体代码(MFIX)，他们可以使用它来改进现有模型，这些模型用于评估和优化用于二氧化碳捕获和其他清洁能源应用的沸腾床设计。

1134500PI: Subramaniam, ShankarTechnologies for clean energy generation from fossil or bio-based fuels and the capture of resulting CO2 emissions use fluidized bed reactors with particles of size and density corresponding to the Geldart A and Geldart B classification. These gas-solid systems exhibit non-uniform and heterogeneous flow structures arising from hydrodynamic instabilities at the particle scale. While theoretical estimates for the stability of a homogeneous gas-solid suspension exist for Stokes flow, the regime of finite fluid inertia is yet unexplored. Design and scale-up of industrial devices that implement clean energy technologies increasingly rely on computational fluid dynamics (CFD) simulations that solve yet untested averaged conservation equations. An important validation test for averaged multiphase flow models is their ability to accurately capture the stability limits of a gas-solid suspension. It is difficult to obtain data from experiments because of limited optical access, but particle-resolved direct numerical simulation (DNS) can provide fully characterized field data to reveal flow physics and to serve as a benchmark for comparative assessment of multiphase flow models. This project will employ a first-principles approach to characterize the stability limits of gas-solid suspensions at finite Reynolds number using particle-resolved DNS. The effects of volume fraction fluctuations and granular temperature will be incorporated to develop a comprehensive stability theory for gas-solid suspensions. The objectives of the project are to: (i) quantify the stability limits of homogeneous gas-solid suspensions with finite fluid inertia for Geldart B particles; (ii) quantify the competing mechanisms of particle-fluid (hydrodynamic) and particle-particle interactions that result in generation of volume fraction fluctuations in gas-solid suspensions using a set-theoretic approach; and (iii) understand the stability and characterize the base state of gas-solid suspensions with finite fluid inertia for Geldart A particles.The DNS data will fill an important gap in our knowledge regarding the stability of gas-solid suspensions with finite fluid inertia. The improved set-theoretic stability theory accounting for volume fraction fluctuations will give additional insight into understanding the dynamics of both Geldart B and Geldart A suspensions, and will remove classical assumptions of scale separation. The DNS data on suspension stability will be made available to the multiphase flow community and will serve as a useful benchmark for CFD codes. The DNS data and stability theory will also be useful for developers of multiphase CFD codes, such as the popular multi-fluid code (MFIX) at the National Energy Technology Laboratory, who may use it to improve existing models that are used to evaluate and optimize fluidized bed design for CO2 capture and other clean energy applications.