Abstract
This review covers the scope of multiscale computational fluid dynamics (CFD), laying the framework for studying hydrodynamics with and without chemical reactions in single and multiple phases regarded as continuum fluids. The molecular, coarse-grained particle, and meso-scale dynamics at the individual scale are excluded in this review. Scoping single-scale Eulerian CFD approaches, the necessity of multiscale CFD is highlighted. First, the Eulerian CFD theory, including the governing and turbulence equations, is described for single and multiple phases. The Reynolds-averaged Navier–Stokes (RANS)-based turbulence model such as the standard k-ε equation is briefly presented, which is commonly used for industrial flow conditions. Following the general CFD theories based on the first-principle laws, a multiscale CFD strategy interacting between micro- and macroscale domains is introduced. Next, the applications of single-scale CFD are presented for chemical and biological processes such as gas distributors, combustors, gas storage tanks, bioreactors, fuel cells, random- and structured-packing columns, gas-liquid bubble columns, and gas-solid and gas-liquid-solid fluidized beds. Several multiscale simulations coupled with Eulerian CFD are reported, focusing on the coupling strategy between two scales. Finally, challenges to multiscale CFD simulations are discussed. The need for experimental validation of CFD results is also presented to lay the groundwork for digital twins supported by CFD. This review culminates in conclusions and perspectives of multiscale CFD.
Highlights
Many scientific problems have intrinsically multiscale nature [1,2]
The microscale volume of fluid (VOF)-computational fluid dynamics (CFD) simulation may be useful for developing correlations that are required in a macroscale CFD simulation for industrial packing columns [74]
This review explored exclusively Eulerian CFD simulations of chemical and biological processes at the multiscale in time and space
Summary
Many scientific problems have intrinsically multiscale nature [1,2]. This multiscale nature often leads to multiple spatial and temporal scales that cross the boundaries of continuum and molecular levels [3]. Tong et al (2019) reviewed multiscale methods divided into a domain decomposition scheme and a hierarchical scheme in fluid flows with heat transfer for coupling MD with particle-based mesoscale methods such as the lattice Boltzmann method (LBM) and CFD [15]. Drikakis et al (2019) presented the application of CFD to the energy field [3], integrated together with molecular dynamics and LBMs. Lu et al (2019) [46] and Wang (2020) [47] reviewed Eulerian CFD approaches for dense gas-solid flows, providing a concise introduction to multiscale methods and highlighting the effects of mesoscale structures (gas bubbles and particle clusters) on the gas-solid Eulerian CFD model, focusing on the energy minimization multi-scale (EMMS) method. Eulerian CFD models in single and multi-phases are first presented, followed by applications of the Eulerian CFD to chemical and biological processes, and the challenges and perspectives of multiscale CFD are discussed
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