By Wolfgang Rodi, George Constantinescu, Thorsten Stoesser
Large-Eddy Simulation (LES), that is a complicated eddy-resolving process for calculating turbulent flows, is used more and more in Computational Fluid Dynamics, additionally for fixing hydraulics and environmental move difficulties. the strategy has usually nice power and is especially fitted to difficulties ruled by way of large-scale turbulent constructions. This e-book offers an advent to the LES approach specifically geared for hydraulic and environmental engineers. in comparison with current books on LES it truly is much less theoretically and mathematically challenging and as a result more uncomplicated to persist with, and it covers unique good points of flows in water our bodies and summarizes the event won with LES for calculating such flows.
The booklet used to be written essentially as an advent to LES for hydraulic and environmental engineers, however it can be very priceless as an access to the topic of LES for researchers and scholars in all fields of fluids engineering. The purposes half will additional be helpful to researchers drawn to the physics of flows ruled by means of the dynamics of coherent constructions.
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Additional resources for Large-Eddy Simulation in Hydraulics
Example text
These stresses, τ ijSGS, are due to the unresolved subgrid-scale motion and need to be modelled, as in the j j filter approach. The face-averaged velocities ui and uj need to be related to the cell-averaged values ui resulting from the solution of the discrete balance equations. For this an interpolation needs to be introduced, and this is discussed in Chapter 4 on Numerical Methods. The resulting discrete equations are in fact the same as those resulting from the filter approach when a top-hat filter is used, the filter width is equal to the grid size and the same discretization approximations for solving numerically the equations are employed.
In LES, the largest scales of the unresolved turbulence, which interact most actively with the resolved motion, are of the size of the filter width Δ. 5) 6/3/2013 5:44:38 PM 26 Large-eddy simulation in hydraulics in which CS is the Smagorinsky constant, an empirical parameter whose value can be obtained from theoretical considerations or a-priori and a-posteriori tests. The determination of the characteristic velocity scale can be done in analogy to Prandtl’s mixing length theory, with the advantage that in LES the length scale is known already.
1 Scale-Similarity Model The Scale-Similarity Model (SSM) of Bardina et al. (1980) does not use the eddy-viscosity concept. Rather, the idea is to assume that the smallest resolved scales are similar to the largest unresolved scales and to use that information to obtain an expression for the SGS stresses τij. This is justified as the most important interactions are those between the largest unresolved (subgrid) scales and the smallest resolved scales. To obtain an expression for τij one has first to define these scales.