Meso-scale modelling

A model was developed earlier which describes the pressure distribution and the velocity through and underneath the clothing around the cylinder (Brasser, 2006). To model the air flow distribution around a human limb, a simplification has been made by assuming this to be a 2-dimensional problem. The body part is represented by a cylinder placed in the air flow. At the front of the (dressed) cyUnder the wind will penetrate the clothing and at the back it will flow back to the environment If only homogeneous perpendicular flow of the outside wind is assumed and the air flow underneath the clothing is modelled only 1-dimensionally, the process can be solved without using CFD. A schematic picture of the setup is shown in Fig. 11.1. 

7 The average velocity through and underneath the clothing, as a function of the air resistance of the clothing. 

Static meso-scale study of the flow around a clothed limb 

Major findings of the latter smdy are surtnnarized in Fig. 11.8, which presents characteristics of heat and mass transfer, averaged over time and angle, as a function of Re (air flow velocity) for varied dimensionless measures of permeability Dale and dimensionless air gap size Ig. 

Please note that, based on the similarity of heat and mass transfer (Sobera et al., 2003), only dimensionless heat transfer characteristics are presented. An 

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The final two chapters discuss modeling of PEFCs. Mukherjee and Wang provide an in-depth review of meso-scale modeling of two-phase transport, while Zhou et al. summarize both the simulation of electrochemical reactions on electrocatalysts and the transport of protons through the polymer electrolyte using atomistic simulation tools such as molecular dynamics and Monte Carlo techniques. 

Meso-Scale Modeling—The Key to Multi-Scale CFD Simulation... 

To meet the industrial demand for both large-scale computation and good predictability, the reasonable way out is not to simulate from the beginning of the micro-scale, but to use coarse-grid simulation with meso-scale modeling for the effects of structure. This kind of approach can be termed the "multi-scale CFD." It is entitled "multi-scale," not because the problem it solves is multi-scale, but because its meso-scale model contains multi-scale structure parameters. 

According to the choice of meso-scale models, we may divide the multi-scale CFD into two branches the "correlative" and the "variational," as named in Li and Kwauk (2003) and will be discussed in the following sections. 

The "correlative" multi-scale CFD, here, refers to CFD with meso-scale models derived from DNS, which is the way that we normally follow when modeling turbulent single-phase flows. That is, to start from the Navier-Stokes equations and perform DNS to provide the closure relations of eddy viscosity for LES, and thereon, to obtain the larger scale stress for RANS simulations (Pope, 2000). There are a lot of reports about this correlative multi-scale CFD for single-phase turbulent flows. Normally, clear scale separation should first be distinguished for the correlative approach, since the finer scale simulation need clear specification of its boundary. In this regard, the correlative multi-scale CFD may be viewed as a "multilevel" approach, in the sense that each span of modeled scales is at comparatively independent level and the finer level output is interlinked with the coarser level input in succession. 

Following the above approach, the correlative multi-scale CFD reduces the computation cost by transforming information over a range of scales into meso-scale models. With these works, it seems feasible to establish a numerical experiment facility to consider thoroughly the... 

The "variational type of multi-scale CFD, here, refers to CFD with meso-scale models featuring variational stability conditions. This approach can be exemplified by the coupling of the EMMS model (Li and Kwauk, 1994) and TFM, where the EMMS/matrix model (Wang and Li, 2007) at the subgrid level is applied to calculate a structure-dependent drag force. 

MESO-SCALE MODELING—THE KEY TO MULTI-SCALE APPROACHES... 

Energy-minimization multi-scale (EMMS) model—a meso-scale model... 

Lu, B., EMMS-based Meso-Scale Model and Its Application in Simulating Gas-Solid Two-Phase Flows, Ph.D. thesis (in Chinese), Institute of Process Engineering, Chinese Academy of Sciences, Beijing (2009). 

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