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International audienceThe flow around single and two side-by-side infinite cylinders is numerically modelled using dynamic Smagorinsky large eddy simulation(LES). For the single cylinder, the Reynolds number based on the diameter and the free stream velocity is 3900. A complete sensitivity study was conducted based on the extrusion length in the span-wise direction, the grid refinement at the wall, the convection scheme, and the sub-grid scale (SGS) model. It was found that the mean solution is not influenced by the extrusion length beyond 4 diameters or by 1% up-winding. However, coarsening the mesh in the wall normal direction or switching off the sub-grid scale model led to drastic effects on the recirculation length and on the underlying velocity field. The two side-by-side cylinders were tested for a range of pitch to diameter ratios (T/D=1.0,1.25≤T/D≤5.0) at a Reynolds number of 3000. For the intermediate pitch to diameter ratios (1.25≤T/D≤1.75), multiple shedding frequencies were detected with a biased wake flow deflection. Furthermore, this biased flow deflection was found to be bistable, i.e., it changes the direction (flipping over) intermittently from one side to the other. This behavior was found to be consistent with reported experimental measurements. During the flip-over from one stable mode to the other, the intermittent gap vortex shedding was found to be stronger than for a stable mode, with in-phase vortex shedding. However, for the higher pitch ratio cases (T/D≥2), a symmetrical wake behavior with anti-phase vortex shedding was observed

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Several modifications are introduced to the Elliptic Blending Differential Flux Model proposed by Shin et al. (2008) to account for the influence of wall blockage on the turbulent heat flux. These modifications are introduced in order to reproduce, in association with the most recent version of the EB-RSM, the full range of regimes, from forced to natural convection, without any case-specific modification. The interest of the new model is demonstrated using analytical arguments, a priori tests and computations in channel flows in the different convection regimes, as well as in a differentially heated cavity.

The present paper focuses on the application of the elliptic blending approach to the modeling of turbulent heat fluxes, in order to account for the influence of solid boundaries. The analytical justification of the extension to the temperature-pressure gradient correlation term of this approach, originally applied to the velocity-pressure gradient, is given. The assumption of weak equilibrium enables the derivation of two new algebraic flux models valid down to the wall. It is shown, with both a priori tests and computations in forced and mixed convection regimes, that the predictions of the streamwise heat-flux and the temperature variance are significantly improved by the use of elliptic blending. A particular attention is devoted to the issue of the modeling of the correlation length scale involved in the elliptic blending for the heat fluxes, which is shown to have a significant influence on the predictions.

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