Very-Large-Eddy Simulations

For the research or assessment mode, the models can be more sophisticated, including the large eddy simulations (LES) or other high-order turbulence closure models, down-scaling with obstacle-resolved computer fluid dynamics (CFD) tools, but such models are very expensive computationally (see e.g., Mahura et al., 2005 [389]). For the forecasting mode, the models have to be fast enough therefore, they use... 

Dirbulence causes swirls or eddies in turbulent flow with different length and time scales. It is almost impossible to accurately computationally describe turbulent flow with all eddies included because this would require very powerful computers. Scientists and engineers have therefore developed different turbulence models, such as k-e model, k-a model, large eddy simulation (LES) model, or direct numerical simulation (DNS) model, which are accurate enough to mimic real-world turbulent flow. 

In considering very many condenser simulations (not just those reviewed here) we have yet to find an application where the differences between any of the multicomponent film models that account for interaction effects (Krishna-Standart, 1976 Toor-Stewart-Prober, 1964 Krishna, 1979a-d Taylor-Smith, 1982) are significant. There is also very little difference between the turbulent eddy diffusivity model and the film models that use the Chilton-Colburn analogy (Taylor et al., 1986). This result is important because it indicates that the Chilton-Colburn analogy, widely used in design calculations, is unlikely to lead to large... 

The Navier-Stokes equations are supposed to describe all types of Newtonian incompressible flow, including turbulent flow. However, modelling of turbulent flow with the Navier-Stokes equations is impractical in most engineering applications, since it requires that even the smallest eddies are resolved. To resolve these eddies, the number of nodes required becomes very large. In addition, the flow does not become stationary, since the eddies seem to move randomly within the flow. These types of time-dependent simulations are very demanding in terms of the number of operations and memory required, and they are too large to be handled by most computers. It is therefore necessary to use simplified models for the modelling of turbulent flow. 

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