Fluid multiscale modeling

Multiscale modeling is an approach to minimize system-dependent empirical correlations for drag, particle-particle, and particle-fluid interactions [19]. This approach is visualized in Eigure 15.6. A detailed model is developed on the smallest scale. Direct numerical simulation (DNS) is done on a system containing a few hundred particles. This system is sufficient for developing models for particle-particle and particle-fluid interactions. Here, the grid is much smaller... 

Figure 55. Physical model for multiscale modelling of particle-fluid system.

If the values of local mean bubble diameter and local gas flux are available, a fluid dynamic model can estimate the required influence of mass transfer and reactions on the fluid dynamics of bubble columns. Fortunately, for most reactions, conversion and selectivity do not depend on details of the inherently unsteady fluid dynamics of bubble column reactors. Despite the complex, unsteady fluid dynamics, conversion and selectivity attain sufficiently constant steady state values in most industrial operations of bubble column reactors. Accurate knowledge of fluid dynamics, which controls the local as well as global mixing, is however, essential to predict reactor performance with a sufficient degree of accuracy. Based on this, Bauer and Eigenberger (1999) proposed a multiscale approach, which is shown schematically in Fig. 9.13. 

VAN DER HoEF, M. A., VAN SiNT AnNALAND, M., DeEN, N. G. KUIPERS, J. A. M. 2008 Numerical simulation of dense gas-solid fluidized beds a multiscale modeling strategy. Annual Review of Fluid Mechanics 40, Al-10. 

Microfluidic and nanofluidic phenomena arising from Lab-on-a-Chip microdevices are characterized by hierarchal multiscale nature with respect not only to space but also to time. In the area of microfluidics and nanofluidics, multiscale modeling aims to develop a viable multiscale computational methodology to study fluid mechanics in spatial and temporal domains ranging from the molecular level to the continuum level. 

Van der Hoef MA, Van Sint Annaland M, DeenNG, Kuipers JAM Numerical simulation of dense gas-sobd fluidized beds a multiscale modeling strategy, Annu Rev Fluid Mech 40 47-70, 2008. 

In most microfluidics and nanofluidics, the atomistic effects on electroosmotic flows are neghgible. But when the characteristic length is comparable with the molecular size of fluid, it should be considered. Molecular dynamics methods have been used to simulate the particle effects in nanoscale electroosmotic flows [23, 24]. However, it is too time-consuming to simulate a real electroosmotic micro- and nanofluidics by molecular dynamics. The multiscale modeling and analysis would be a possible research direction. 

Much of the interest in multiscale modeling methods is based on the premise that, one day, the behavior of entirely new materials or complex fluids will be... 

While multiscale modeling is still in its infancy, its promise is such that considerable efforts should be devoted to its development in the years to come. A few examples have started to appear in the literature. In the case of solid materials, the challenge of coupling atomistic phenomena (e.g., the tip of a crack) with mechanical behavior (e.g., crack propagation and failure) over macroscopic domains has been addressed by several authors. In the case of fluids, molecular-level structure (e.g., the conformation of DNA molecules in solution) has been... 

Menter, F. R. Multiscale model for turbulent flows in 24th fluid dynamic conference. Am. Inst. Aeronaut. Astronaut. 1993. 

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