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

1134500 PI：Subramaniam，Shankar用于从化石或生物基燃料产生清洁能源和捕获所产生的CO2排放的技术使用流化床反应器，其颗粒的尺寸和密度对应于GeldartA和B分类。这些气固系统表现出非均匀和非均匀的流动结构所产生的流体动力学不稳定性在颗粒尺度。虽然存在对斯托克斯流的均匀气固悬浮液的稳定性的理论估计，但有限流体惯性的状态尚未探索。实施清洁能源技术的工业设备的设计和规模扩大越来越依赖于计算流体动力学（CFD）模拟，该模拟解决了尚未测试的平均守恒方程。平均多相流模型的一个重要验证测试是它们准确捕获气固悬浮液稳定性极限的能力。由于光学通道有限，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，以揭示流动物理学，并作为多相流模型比较评估的基准。本计画将采用第一性原理的方法，利用粒子解析DNS来描述有限雷诺数下气固悬浮液的稳定极限。体积分数波动和颗粒温度的影响将被纳入发展一个全面的稳定性理论的气-固悬浮液。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极限;（ii）量化颗粒-流体的竞争机制（流体动力学）和颗粒-颗粒相互作用，其导致使用集合理论方法在气-固悬浮液中产生体积分数波动;以及（iii）理解GeldartA颗粒在有限流体惯性下气固悬浮液的稳定性并表征其基态。DNS数据将填补我们关于有限流体惯性下气固悬浮液稳定性知识的重要空白。改进的集理论的稳定性理论占体积分数波动将提供额外的洞察力来理解Geldart B和Geldart A悬浮液的动态，并将删除经典的尺度分离的假设。关于悬浮稳定性的DNS数据将提供给多相流社区，并将作为计算流体动力学代码的有用基准。DNS数据和稳定性理论也将有助于多相CFD代码的开发人员，例如国家能源技术实验室的流行多流体代码（MFIX），他们可以使用它来改进用于评估和优化CO2捕获和其他清洁能源应用的流化床设计的现有模型。

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.