Very-Large Eddy Simulation (V-LES) of the flow across a tube bundle

A new turbulence modelling approach (Very-Large Eddy Simulation; V-LES) is developed and compared to conventional RANS and LES for a flow across a tube bundle. The method, which belongs to the large-scale simulation category, represents a good compromise between efficiency and precision, and may thus be used for industrial problems for which LES remains computationally expensive under high to very-high Reynolds number flow conditions. It can also be used for gas-liquid two-phase flows such as pressurized thermal shocks. The method is a sort of blend between U-RANS and LES, in that it resolves very large structures - way larger than the grid size - and models all subscale of turbulence using a two-equation model, by reference to RANS. The original model is shown here to share the same characteristics as the Detached Eddy Simulation (DES) approach, in that when the filter width is smaller than the wall-distance at which viscous effects are negligible (f(mu) = 1), the fixed filter width is replaced by the wall distance. First conclusions to be drawn from its extension here is that the flow must be resolved in three-dimensions, under transient conditions, with refined grids. Sensitivity to various computational parameters has been addressed: grid, filter width, domain size, and inflow conditions. This modelling strategy is proved to provide the flow unsteadiness in three-dimensions, while saving computational cost compared to LES. The method is computationally efficient (it can be applied using an implicit solver which permits a higher CFL than with LES; typically 1 versus 0.1), and numerically robust. The computational cost decreases with increasing filter width, though at the expenses of the quality of the results. (C) 2011 Elsevier B.V. All rights reserved.